Acute Vision Loss
Acute vision loss is the sudden partial or complete loss of vision in one or both eyes, resulting from ocular, neurological, or vascular causes requiring urgent evaluation.
Acute Visual Loss
Acute visual loss (AVL) refers to a sudden or rapid decline in visual acuity or visual field that occurs over seconds to days (typically < 72 hours). It is an ophthalmic emergency until proven otherwise, as many causes are time-sensitive and delay in diagnosis can result in permanent, irreversible blindness.
The word "acute" here distinguishes it from chronic/gradual visual loss (e.g., cataract, chronic glaucoma, age-related macular degeneration), which develops over weeks to months/years.
Key conceptual point: Acute visual loss is a symptom, not a diagnosis. The clinical approach requires systematic localization along the visual pathway — from the tear film and cornea at the front, through the lens, vitreous, retina, optic nerve, chiasm, optic tract, and all the way to the occipital cortex — to determine the underlying cause. [1][2]
2. Epidemiology and Risk Factors
- Acute visual loss accounts for a significant proportion of ophthalmic emergency presentations
- In Hong Kong, retinal vascular disease (especially retinal vein occlusion and diabetic complications) and acute angle-closure glaucoma (AACG) are particularly common causes [1][3]
- AACG has a higher prevalence in East Asian populations (shallower anterior chambers, shorter axial lengths) — this is an important Hong Kong–relevant point
- Giant cell arteritis (GCA) is the commonest primary vasculitis causing visual loss in the elderly but is less common in Asian populations compared to Caucasians (incidence ~20/100k/y in those > 50y in Western populations, lower in HK) [4]
- Central retinal artery occlusion (CRAO): incidence 1–10/100k, mean age 60–65y, M > F [5]
- Vitreous haemorrhage: relatively common cause of acute visual loss (incidence ~7/100k) [6]
| Cause | Key Risk Factors |
|---|---|
| Retinal artery occlusion | HTN, smoking, DM, carotid atherosclerosis, AF, valvular heart disease, hypercoagulable states [5] |
| Retinal vein occlusion | HTN (strongest), DM, hyperlipidaemia, glaucoma, hyperviscosity states |
| Acute angle-closure glaucoma | East Asian ethnicity, hypermetropia (far-sightedness), shallow anterior chamber, female sex, older age, dim lighting, mydriatic drugs |
| Retinal detachment | High myopia, prior cataract surgery, trauma, lattice degeneration, FHx |
| Vitreous haemorrhage | Proliferative diabetic retinopathy, posterior vitreous detachment, trauma, coagulopathy [6] |
| Optic neuritis | Young female, MS, NMOSD, MOG-IgG disease [7] |
| Arteritic anterior ischaemic optic neuropathy (AAION/GCA) | Age > 50, female, PMR, ↑ESR/CRP [4] |
| Non-arteritic AION (NAION) | "Disc at risk" (small cup-to-disc ratio), HTN, DM, nocturnal hypotension, OSA |
3. Anatomy and Function of the Visual Pathway
Understanding the anatomy is essential because the pattern of visual loss directly localizes the lesion.
The visual pathway begins with light entering the eye. For a clear image to reach the retina, the ocular media must be transparent:
- Cornea → the main refractive surface (2/3 of total refractive power)
- Anterior chamber → filled with aqueous humour; if blood (hyphaema) or inflammatory cells (hypopyon) accumulate here, vision is impaired
- Lens → fine-tunes focus (accommodation); opacification = cataract
- Vitreous humour → gel-like substance filling the posterior segment; blood (vitreous haemorrhage) or inflammatory debris can block light
Any opacity in the ocular media (corneal oedema, hyphaema, lens opacity, vitreous haemorrhage) can cause acute visual loss. [1][2]
- The retina is the neural tissue lining the posterior globe
- It contains photoreceptors (rods for scotopic/dim-light vision, cones for photopic/colour/central vision)
- The macula is the central area of the retina responsible for fine central vision; the fovea at its centre has the highest density of cones
- The retina has a dual blood supply:
- Central retinal artery (CRA) (branch of ophthalmic artery → internal carotid artery): supplies the inner retina (ganglion cells, inner nuclear layer)
- Choroidal circulation (from posterior ciliary arteries): supplies the outer retina (photoreceptors, RPE)
- ~15% of people have a cilioretinal artery (from ciliary circulation) that supplies the macular region — this is why some patients with CRAO retain central vision ("macula-sparing") [5]
This dual supply explains the cherry-red spot in CRAO: the macula is thin (no inner retinal layers at fovea), so the intact choroidal circulation shows through as a red spot against the surrounding pale, ischaemic (swollen, opaque) inner retina. In ophthalmic artery occlusion, even the choroidal supply is lost, so the cherry-red spot may be absent. [5]
- Optic nerve (CN II): Axons of retinal ganglion cells converge at the optic disc (the "blind spot") and exit the globe as the optic nerve
- The optic nerve passes through the optic canal into the middle cranial fossa
- Optic chiasm: Nasal fibres (carrying temporal visual field information) cross; temporal fibres (carrying nasal visual field information) do not
- A lesion at the chiasm (e.g., pituitary tumour) → bitemporal hemianopia [8]
- Optic tract → lateral geniculate nucleus (LGN) → optic radiations → primary visual cortex (V1, occipital lobe)
- Lesions posterior to the chiasm → homonymous hemianopia (contralateral to the side of the lesion)
- Bilateral occipital lobe infarction → cortical blindness (pupils remain reactive because the pupillary reflex pathway is subcortical) [2]
Understanding this is critical because the relative afferent pupillary defect (RAPD, or Marcus Gunn pupil) is one of the most important signs in acute visual loss.
- Afferent limb: Retina → optic nerve → partial decussation at chiasm → both pretectal nuclei (midbrain)
- Efferent limb: Pretectal nuclei → bilateral Edinger-Westphal nuclei → CN III → ciliary ganglion → sphincter pupillae (constriction)
Because each eye sends signals to both pretectal nuclei, shining light in one eye constricts both pupils (direct and consensual response).
RAPD (swinging flashlight test): When there is a unilateral optic nerve or extensive retinal lesion, the affected eye sends a weaker afferent signal. When the light swings from the normal eye to the affected eye, the affected pupil paradoxically dilates (because the "bright stimulus" it perceives is weaker than what the normal eye just provided). RAPD is always present in CRAO regardless of macular sparing. [5]
High Yield Exam Point
RAPD localizes the lesion to the retina (if extensive) or optic nerve on the affected side. It does NOT occur in media opacity (cataract, vitreous haemorrhage) or in purely macular disease (too little retinal area affected), or in refractive error. A positive RAPD in a patient with acute visual loss should make you think: retinal artery/vein occlusion, optic neuritis, ischaemic optic neuropathy, or compressive optic neuropathy. [1][2]
4. Aetiology and Pathophysiology
The causes of acute visual loss are best organized anatomically — from front to back along the visual pathway. For each, the pathophysiology is explained.
4.1 Ocular Media Causes (Cornea, Anterior Chamber, Lens, Vitreous)
- Etymology: "Glaucoma" from Greek glaukos = bluish-green (describing the appearance of the cornea)
- Pathophysiology: In a predisposed eye (shallow anterior chamber, thick lens), the iris can be pushed forward (pupillary block mechanism), physically blocking the trabecular meshwork at the drainage angle. Aqueous humour cannot drain → intraocular pressure (IOP) rises rapidly (often > 40–60 mmHg, normal 10–21 mmHg) → corneal oedema (explains hazy vision and halos around lights), ischaemic damage to the optic nerve, and retinal ischaemia [1][3]
- Why halos? Corneal oedema causes light to scatter and diffract, producing rainbow-coloured halos around point light sources
- Why mid-dilated fixed pupil? The high IOP causes iris sphincter ischaemia → the pupil cannot constrict. Sympathetic tone causes partial dilation. The pupil is therefore "mid-dilated" (4–6 mm) and non-reactive
AACG is particularly relevant in Hong Kong due to higher prevalence in East Asian populations. [1][3]
- Severe corneal infection (bacterial, viral e.g., HSV) or corneal ulceration can cause acute visual loss through corneal opacification
- Contact lens wear is a major risk factor for microbial keratitis
- Pathophysiology: infection → inflammatory infiltrate → corneal opacity → blocked light transmission
- Aetiology: proliferative diabetic retinopathy (most common), posterior vitreous detachment (PVD) ± retinal tear, ocular trauma, coagulopathy [6]
- Pathophysiology: Blood enters the vitreous cavity from ruptured normal vessels (trauma, PVD tearing a vessel) or from pathological neovascularization (PDR). Blood in the vitreous blocks light from reaching the retina → sudden painless visual loss
- Clinical pearl: "worse in the morning" because blood settles on the macula overnight when supine [6]
- Patients may describe "red hues," floaters, shadows, or "cobwebs"
- Inflammation of the uveal tract (iris, ciliary body, choroid)
- Anterior uveitis → inflammatory cells and protein ("flare") in the anterior chamber → reduces media clarity
- Causes include HLA-B27–associated diseases (ankylosing spondylitis), sarcoidosis, Behçet's disease, infections
- Usually presents with painful red eye, photophobia, and blurred vision rather than profound visual loss
4.2 Retinal Causes
- Etymology: "Central" = main trunk; "retinal" = retinal vasculature; "artery" = arterial supply; "occlusion" = blockage
- Aetiology: usually embolic in origin [5]
- Pathophysiology: Embolus lodges at the narrowest point of the CRA (at the lamina cribrosa where the artery enters the eye). Inner retinal layers are deprived of blood supply → retinal ganglion cell death begins within minutes. The retina has no ischaemic tolerance — irreversible damage occurs within 90–100 minutes (similar to brain tissue)
- Fundoscopy: ischaemic retinal whitening + oedema, cherry-red spot over macula, attenuated arteries, ± visible embolus (Hollenhorst plaque) [5]
- RAPD is ALWAYS present regardless of macular sparing [5]
CRAO = Stroke Equivalent
- Embolus lodges in a branch of the CRA → ischaemia of a sector of retina → sudden monocular loss of a specific visual field [5]
- Fundoscopy: sectoral retinal whitening, partial cherry-red spot, embolus more commonly seen than in CRAO (~2/3) [5]
- Less than half have impaired visual acuity (because the macula may be spared)
- Pathophysiology: Thrombotic occlusion of the central retinal vein (at the lamina cribrosa, where the vein and artery share a common adventitial sheath — atherosclerotic thickening of the artery can compress the vein). Venous congestion → increased hydrostatic pressure → haemorrhages, oedema, and ischaemia
- Fundoscopy of CRVO: "blood and thunder" or "pizza pie" fundus — widespread flame-shaped haemorrhages in all four quadrants, dilated tortuous veins, cotton wool spots, disc oedema, macular oedema
- BRVO: similar but confined to the territory of the affected branch vein
- Risk factors: HTN (strongest), DM, hyperlipidaemia, glaucoma, hyperviscosity (e.g., polycythaemia vera, leukaemia)
- Classification:
- Non-ischaemic (mild/moderate): Better prognosis, fewer haemorrhages
- Ischaemic (severe): Poorer prognosis, extensive haemorrhages, ↑risk of neovascularization → neovascular glaucoma ("90-day glaucoma")
- Types:
- Rhegmatogenous (most common): "rhegma" = Greek for break/tear. A retinal tear allows liquefied vitreous to track under the neurosensory retina, separating it from the RPE
- Tractional: Fibrovascular proliferation (e.g., in PDR) pulls the retina off the RPE
- Exudative/serous: Fluid accumulates under the retina without a tear (e.g., in severe HTN, tumours, inflammatory conditions)
- Pathophysiology of rhegmatogenous RD: Age-related vitreous liquefaction and syneresis → posterior vitreous detachment (PVD) → if the vitreous is adherent to the retina at certain points, traction during PVD creates a retinal tear → liquid vitreous enters through the tear → neurosensory retina detaches from RPE → photoreceptors lose their metabolic support from the RPE and choroidal circulation → progressive visual loss
- Warning symptoms (prodrome of PVD ± retinal tear):
The significance of flashing lights (photopsia) in a patient with new floaters is that it indicates vitreous traction on the retina — this is a warning sign for retinal tear and impending retinal detachment. These patients need urgent dilated fundoscopy. [9]
- Progressive visual field loss: Patients classically describe a "curtain" or "shadow" coming across the vision — this corresponds to the area of detached retina
- If macula detaches ("macula-off"): Central vision is lost, and even with successful reattachment surgery, visual recovery is poorer
- Includes central serous chorioretinopathy (CSCR), acute wet age-related macular degeneration (AMD)
- Wet AMD: Choroidal neovascularization → subretinal/sub-RPE fluid/blood → sudden central visual distortion (metamorphopsia) or scotoma
- CSCR: Focal RPE dysfunction → serous detachment of the neurosensory retina at the macula → central blurring, often in young-middle aged stressed males or corticosteroid users
4.3 Optic Nerve Causes
- Etymology: "Optic" = relating to vision/optic nerve; "neuritis" = inflammation of a nerve
- Inflammatory demyelination of the optic nerve
- Causes: [7]
- Multiple sclerosis (MS): Most common association in Caucasian populations; ON is the presenting feature in ~1/3 of MS patients
- Neuromyelitis optica spectrum disorder (NMOSD): "neuro" = nerve, "myelitis" = spinal cord inflammation, "optica" = optic nerve involvement. Anti-aquaporin-4 (AQP4) antibodies. More common in Asian populations and tends to be more severe/bilateral
- MOG-IgG disease: Anti-myelin oligodendrocyte glycoprotein antibodies
- Infectious: syphilis, TB, viral
- Post-infectious / post-vaccination
- Pathophysiology: Immune-mediated demyelination of the optic nerve → impaired signal conduction → visual loss. Inflammation causes pain (the optic nerve sheath is innervated by meningeal branches of the trigeminal nerve, and the inflamed nerve swells within its sheath)
- Why pain on eye movement? The extraocular muscles (especially medial and superior rectus) insert close to the optic nerve sheath. Movement tugs on the inflamed nerve
- Clinical features:
- Subacute unilateral visual loss (develops over hours to days, reaches nadir over 1–2 weeks)
- Pain: retro-orbital, worsened by eye movement
- ↓Visual acuity, ↓colour vision (dyschromatopsia — tested with Ishihara plates), RAPD positive
- Fundoscopy: may show optic disc oedema (papillitis, ~1/3) or may be normal (retrobulbar neuritis — "the patient sees nothing and the doctor sees nothing", ~2/3)
- Optic atrophy on fundoscopy in chronic/recurrent cases [7]
Optic Neuritis vs AION
Both cause acute monocular visual loss with RAPD. Key distinguishing features: Optic neuritis is typically in younger patients (20–40y), painful (especially on eye movement), and associated with MS/NMOSD. AION is typically in older patients ( > 50y), painless, and associated with vascular risk factors (NAION) or GCA (AAION). [1][2][4]
B. Ischaemic Optic Neuropathy
- Pathophysiology: giant cell (granulomatous) arteritis of the posterior ciliary arteries → ischaemia of the optic nerve head [4]
- GCA is a sight-threatening disease; the importance of timely diagnosis and treatment cannot be overstated [4][10]
- The posterior ciliary arteries (branches of the ophthalmic artery) supply the optic nerve head. Granulomatous inflammation → luminal narrowing/occlusion → optic nerve infarction
- Clinical features:
- Sudden, severe, painless visual loss (may be preceded by amaurosis fugax — warning sign!)
- Associated symptoms: new temporal headache, jaw claudication, scalp tenderness, PMR symptoms (proximal girdle pain/stiffness), constitutional symptoms (fever, weight loss, malaise) [4]
- Signs: tender, prominent, non-pulsatile temporal artery; ↓temporal artery pulse
- Fundoscopy: chalky white, swollen optic disc with haemorrhages ("pallid disc oedema") [4]
- If untreated, risk of fellow eye involvement within days to weeks (up to 50%) — this is why it is a true ophthalmic emergency
Any patient > 50 years old presenting with acute visual loss must have GCA excluded. Check ESR and CRP urgently. Do NOT wait for biopsy results before starting high-dose steroids. [4][10]
- Most common cause of acute optic neuropathy in patients > 50y
- Pathophysiology: Presumed small-vessel ischaemia of the optic nerve head (watershed zone between the posterior ciliary artery territories). Often occurs overnight ("wake up with visual loss") — nocturnal hypotension reduces perfusion pressure to a critically small disc
- "Disc at risk": Small cup-to-disc ratio → crowded optic disc → predisposes to compartment syndrome–like ischaemia during low perfusion states
- Fundoscopy: swollen, hyperaemic disc (not as pale as AAION), often with sectoral oedema and haemorrhages
- Usually less severe visual loss than AAION; altitudinal visual field defect is classic (inferior > superior)
- No proven treatment (unlike AAION, steroids do not help)
- Pituitary tumour → compression of optic chiasm → bitemporal hemianopia [8]
- Other causes: meningioma, orbital tumour, thyroid eye disease (apical crowding → compressive optic neuropathy in Graves' orbitopathy) [11]
- Graves' ophthalmopathy: oversized recti + orbital fat → apical crowding → compressive optic neuropathy; symptoms include slowly progressive ↓vision (especially colour vision, contrast sensitivity); signs include optic disc oedema/pallor, RAPD+, central scotoma with inferior arcuate defects [11]
- Pituitary apoplexy (acute haemorrhage/infarction of a pituitary adenoma) can cause acute visual loss — this is a neurosurgical emergency
- Bilateral optic disc swelling due to raised ICP
- Pathophysiology: ↑ICP → impaired axoplasmic flow in the optic nerve → disc swelling
- Visual acuity is typically preserved initially (unlike optic neuritis or AION), but there is enlargement of the blind spot and transient visual obscurations (seconds-long episodes of greying/blacking out of vision, often with postural change)
- If chronic/untreated → progressive visual field loss and eventual optic atrophy
4.4 Neuro-Ophthalmic/Central Causes
- Posterior cerebral artery (PCA) infarction → contralateral homonymous hemianopia
- Bilateral PCA infarction → cortical blindness (pupils normal, patient may deny blindness — Anton's syndrome)
- Patients with homonymous hemianopia may describe "can't see on one side" and may bump into objects on the affected side
- Acute haemorrhage or infarction of a pituitary adenoma → sudden expansion → compression of optic chiasm and surrounding structures
- Acute bitemporal hemianopia, headache, ophthalmoplegia (CN III, IV, VI run through the cavernous sinus adjacent to the pituitary), altered consciousness [8]
- Amaurosis fugax ("fugax" = Latin for fleeting): painless transient monocular visual loss, typically lasting seconds to minutes [2][4]
- Causes: retinal artery insufficiency (embolic, e.g., carotid atherosclerosis), GCA, vasospasm (migraine)
- This is a warning sign for impending CRAO or stroke and demands urgent investigation
- Migraine aura: Scintillating scotomas, zigzag lines (fortification spectra), typically bilateral and lasting 15–30 minutes, followed by headache. Visual phenomena are positive (see things that aren't there) rather than negative (loss of vision)
- Papilloedema-related transient visual obscurations: Brief (seconds), bilateral, related to posture
- Traumatic optic neuropathy: Direct or indirect (shearing forces transmitted to the optic canal) damage to the optic nerve
- Orbital/globe injury: Hyphaema, lens dislocation, vitreous haemorrhage, retinal detachment, globe rupture
- Chemical injury: Alkali burns are worse than acid (alkali penetrates deeper — saponification of cell membranes)
5. Classification of Acute Visual Loss
| Pattern | Localization | Examples |
|---|---|---|
| Unilateral | Pre-chiasmal (eye or optic nerve) | CRAO, CRVO, retinal detachment, vitreous haemorrhage, optic neuritis, AION, AACG |
| Bilateral | Chiasmal, retrochiasmal, or bilateral pre-chiasmal | Bilateral occipital infarct, pituitary apoplexy, bilateral optic neuritis (NMOSD), methanol poisoning |
| Visual field defect | Depends on location along pathway | Homonymous hemianopia (post-chiasmal), bitemporal hemianopia (chiasmal), altitudinal defect (AION) |
| Painful | Painless |
|---|---|
| Acute angle-closure glaucoma | CRAO / BRAO |
| Optic neuritis | CRVO / BRVO |
| Keratitis / corneal ulcer | Retinal detachment |
| Endophthalmitis | Vitreous haemorrhage |
| Scleritis | AION (both AAION and NAION) |
| Trauma | Wet AMD |
| GCA-related headache (but the visual loss itself in AAION is painless) | Occipital stroke |
| Onset | Duration | Think |
|---|---|---|
| Sudden (seconds) | Persistent | Vascular: CRAO, CRVO, AION, vitreous haemorrhage, retinal detachment |
| Sudden | Transient (seconds-minutes) | Amaurosis fugax, papilloedema-related TVOs, migraine aura |
| Subacute (hours-days) | Progressive | Optic neuritis, AACG, endophthalmitis |
6. Clinical Features
6.1 Symptoms
The history is the most important tool in localizing the cause of acute visual loss. Systematically ask about:
| Symptom | Pathophysiological Basis | Differential Diagnosis |
|---|---|---|
| Sudden, profound, painless monocular visual loss | Acute vascular interruption to retina or optic nerve | CRAO, AAION, NAION |
| Sudden painless monocular visual loss with "curtain" or "shadow" | Progressive retinal detachment — the detached area corresponds to the visual field loss | Rhegmatogenous retinal detachment |
| Sudden painless visual loss, worse in morning | Blood settles on macula overnight | Vitreous haemorrhage [6] |
| Subacute monocular visual loss with pain on eye movement | Demyelinating inflammation of optic nerve; eye movement tugs on inflamed nerve sheath | Optic neuritis |
| Sudden painful monocular visual loss + red eye + nausea/vomiting | Acute ↑IOP → corneal oedema, retinal ischaemia; vagal reflex → N/V | AACG |
| Transient monocular visual loss (seconds-minutes) | Transient retinal ischaemia from embolus, vasospasm, or vasculitis | Amaurosis fugax (carotid disease, GCA, migraine) [2] |
| Bilateral positive visual phenomena (zigzag lines, scintillations) lasting 15-30 min | Cortical spreading depression in occipital cortex | Migraine aura |
| Bilateral homonymous visual field loss | Post-chiasmal ischaemia | PCA stroke, pituitary apoplexy |
| Associated Symptom | Significance | Pathophysiological Basis |
|---|---|---|
| Floaters ("cobwebs," "strands," "specks") | PVD ± retinal tear, vitreous haemorrhage | Condensation of vitreous collagen, blood, or pigment cells in vitreous cast shadows on retina [6][9] |
| Flashes of light (photopsia) | Vitreous traction on retina — warning sign for retinal tear/detachment | Mechanical stimulation of photoreceptors by vitreous traction generates the same signal as light [9] |
| Halos around lights | AACG | Corneal oedema from ↑IOP causes diffraction of light |
| Metamorphopsia (distortion of straight lines) | Macular pathology: wet AMD, CSCR, macular oedema | Distortion of photoreceptor alignment at the macula by subretinal fluid or neovascularization |
| Temporal headache (new onset, unilateral) | GCA | Granulomatous inflammation of the temporal artery branches |
| Jaw claudication | GCA (most specific symptom) | Ischaemia of the masseter muscle due to maxillary artery vasculitis [4] |
| Scalp tenderness | GCA | Inflammation of scalp arteries |
| PMR symptoms (proximal girdle stiffness, worse in morning) | GCA + PMR overlap | Shared inflammatory disease process [4][10] |
| Neurological symptoms (contralateral weakness, sensory loss, dysphasia) | Stroke | Anterior or posterior circulation ischaemia |
| Eye pain, redness, photophobia | AACG, keratitis, uveitis, scleritis, endophthalmitis | Inflammation or ↑IOP affecting pain-sensitive structures |
| Recent trauma | Traumatic optic neuropathy, retinal detachment, vitreous haemorrhage, globe rupture | Direct or indirect injury |
| Contact lens wear | Microbial keratitis | Corneal hypoxia and micro-trauma from contact lens → bacterial entry |
Must-Ask Questions in Acute Visual Loss
When a patient presents with acute visual loss, always ask: [1][2][9]
- One eye or both? (laterality → pre-chiasmal vs chiasmal/retrochiasmal)
- Painful or painless? (inflammatory/↑IOP vs vascular)
- Central or peripheral vision affected? (macular vs peripheral retinal pathology)
- Transient or persistent? (vascular insufficiency/TIA vs structural)
- Any flashes or floaters? (retinal tear/PVD warning)
- Any headache, jaw claudication, scalp tenderness? (GCA screen)
- Any associated neurological symptoms? (stroke)
- Any nausea/vomiting with eye pain? (AACG)
- Preceding trauma? (traumatic causes)
- Medical history: DM, HTN, AF, carotid disease, inflammatory disease, recent surgery
6.2 Signs
- Tested with Snellen chart, one eye at a time, with spectacles on [2]
- VA expressed as d/D (d = distance at which patient reads, D = distance at which a normal person can read the same line) [2]
- If VA < 6/9 → suspect refractive error → correct with pinhole (pinhole eliminates refractive error by reducing the aperture; if VA improves, the problem is refractive, not pathological) [2]
- If VA < 6/120 (can't read first row): [2]
- Can the patient count fingers (CF)?
- If no, can they detect hand movements (HM)?
- If no, can they detect light perception (LP)?
- If no → no light perception (NLP) — worst possible VA
| Condition | Typical VA |
|---|---|
| CRAO | Usually HM or worse (profound loss) |
| BRVO | Variable (6/6 if macula spared) |
| Optic neuritis | Variable (6/12 to NLP) |
| Retinal detachment | Variable (depends on macula involvement) |
| AACG | Markedly reduced |
| Vitreous haemorrhage | Variable (depends on density) |
- RAPD (relative afferent pupillary defect) — tested with swinging flashlight test [1][2]
- Present in: CRAO, optic neuritis, AION, extensive retinal detachment, any significant unilateral optic nerve pathology
- Absent in: Media opacity alone (cataract, vitreous haemorrhage), purely macular disease, refractive error, retrochiasmal lesions (because both eyes' afferent signals have mixed by then)
- Fixed mid-dilated pupil: AACG (iris sphincter ischaemia from ↑IOP)
A normal pupil examination (no RAPD) in a patient with significantly reduced VA in one eye should make you consider: media opacity, macular disease, refractive error, or functional (non-organic) visual loss. A positive RAPD with good VA means look for a large peripheral retinal or optic nerve lesion that hasn't yet affected central acuity. [1][2]
| Pattern | Localization |
|---|---|
| Central scotoma | Macular disease, optic neuritis |
| Altitudinal defect (superior or inferior half) | AION (classically inferior altitudinal) |
| Arcuate scotoma | Glaucoma, branch vascular occlusion |
| "Curtain" (progressive field loss from periphery) | Retinal detachment |
| Bitemporal hemianopia | Chiasmal compression (pituitary tumour) [8] |
| Homonymous hemianopia | Retrochiasmal (optic tract, LGN, radiations, occipital cortex) |
| Monocular temporal visual field loss | Nasal retinal pathology or nasal optic nerve lesion |
| Sign | Condition | Pathophysiological Basis |
|---|---|---|
| Conjunctival injection (ciliary flush — perilimbal) | AACG, uveitis, keratitis | Inflammation or ↑IOP → dilation of deep episcleral/ciliary vessels preferentially around the limbus (where the ciliary body sits) |
| Corneal haze/oedema | AACG | ↑IOP overwhelms the corneal endothelial pump → fluid accumulates in the corneal stroma |
| Shallow anterior chamber | AACG | Predisposing anatomy; iris bowed forward |
| Hypopyon (layered white cells in anterior chamber) | Endophthalmitis, severe uveitis | Inflammatory exudate settling inferiorly by gravity |
| Hyphaema (blood in anterior chamber) | Trauma, rubeosis iridis | Ruptured iris or angle vessels |
| Mid-dilated fixed pupil | AACG | Iris sphincter ischaemia from ↑IOP [1] |
| Proptosis | Orbital cellulitis/abscess, carotid-cavernous fistula, thyroid eye disease | Mass effect or vascular engorgement in the orbit pushing the globe forward |
| Tender, prominent, non-pulsatile temporal artery | GCA | Granulomatous inflammation → vessel wall thickening, ↓pulsation [4] |
This is arguably the single most important examination in acute visual loss.
| Fundoscopic Finding | Condition | Pathophysiological Basis |
|---|---|---|
| Cherry-red spot + pale retina + attenuated arteries | CRAO | Inner retina is infarcted and oedematous (whitened); macula is thin (no inner retinal layers at fovea) so choroidal vasculature shows through as "red" [5] |
| Sectoral retinal whitening + visible embolus | BRAO | Ischaemia in the territory of the blocked branch artery [5] |
| Widespread flame haemorrhages, dilated tortuous veins, cotton wool spots, disc oedema ("blood and thunder") | CRVO | Venous congestion → back-pressure → haemorrhages and oedema |
| Sectoral flame haemorrhages | BRVO | Same as CRVO but localized to one sector |
| Swollen, pale/chalky white disc with haemorrhages | AAION (GCA) | Posterior ciliary artery ischaemia → optic nerve infarction [4] |
| Swollen, hyperaemic disc with sectoral oedema | NAION | Small-vessel ischaemia of the optic nerve head, less severe than AAION |
| Disc oedema (papillitis) or normal disc (retrobulbar neuritis) | Optic neuritis | Demyelinating inflammation of the optic nerve [7] |
| Bilateral disc oedema | Papilloedema | ↑ICP → impaired axoplasmic flow |
| Elevated/detached retina, ± retinal tear, ± tobacco dust (Shafer's sign = pigment in anterior vitreous) | Retinal detachment | Separation of neurosensory retina from RPE |
| Loss of red reflex + blood in vitreous | Vitreous haemorrhage | Blood in vitreous cavity blocks light and the view of the fundus [6] |
| Microaneurysms, dot-and-blot haemorrhages, hard exudates, cotton wool spots, neovascularization | Diabetic retinopathy | Retinal microangiopathy → ischaemia → neovascularization [12] |
Key Examination Tip
In acute visual loss, always perform: (1) Visual acuity, (2) Pupil examination including swinging flashlight test for RAPD, (3) Confrontation visual fields, (4) Anterior segment examination (red eye? shallow anterior chamber? corneal clarity?), (5) Fundoscopy. [1][2] A simple physical exam that can be done in any clinic: the swinging flashlight test (for RAPD) — this requires only a pen torch and is the single most useful bedside test. [9]
- Normal: 10–21 mmHg
- AACG: IOP often > 40–60 mmHg → rock-hard globe on palpation (can compare with palpation of the normal eye through closed eyelids as a rough screen)
- CRVO: ↑IOP is both a risk factor and a complication (neovascular glaucoma)
- Test for cranial nerve palsies (CN III, IV, VI → ophthalmoplegia), motor/sensory deficits (stroke), and signs of ↑ICP (papilloedema, altered consciousness)
High Yield Summary
Acute Visual Loss — Key Points for Exams:
- Acute visual loss is a symptom, not a diagnosis — systematic anatomical localization is the approach
- Key history questions: laterality, pain, transient vs persistent, flashes/floaters, GCA symptoms, neurological symptoms
- Key examinations: VA (Snellen chart, pinhole correction), RAPD (swinging flashlight test — most useful bedside test), confrontation visual fields, anterior segment (red eye, corneal clarity, pupil shape/reactivity, anterior chamber depth), fundoscopy, IOP
- RAPD = optic nerve or extensive retinal lesion on the affected side. Absent in media opacity, macular disease, refractive error, retrochiasmal lesions
- CRAO = stroke equivalent — needs urgent vascular workup. Fundus: cherry-red spot + pale retina + attenuated arteries. RAPD always present
- GCA (AAION) = ophthalmic emergency in elderly ( > 50y). Must check ESR/CRP. Start high-dose steroids BEFORE biopsy. Jaw claudication is most specific symptom. Risk of fellow eye involvement if untreated
- Optic neuritis: young patient, painful (worse on eye movement), subacute, ↓colour vision, RAPD+. Associated with MS, NMOSD, MOG-IgG disease
- AACG: painful red eye, halos, N/V, mid-dilated fixed pupil, shallow anterior chamber, very high IOP. More common in East Asians
- New floaters + flashes = PVD ± retinal tear → urgent dilated fundoscopy to rule out retinal tear/detachment
- Vitreous haemorrhage: sudden painless visual loss, worse in morning, loss of red reflex. Most common cause = proliferative DR
Active Recall - Acute Visual Loss
[1] Lecture slides: GC 121. Acute Visual Loss.pdf [2] Senior notes: Ryan Ho Opthalmology.pdf (Ch 1 — Ophthalmic History, Ch 2 — Visual Acuity) [3] Lecture slides: 2024 General Clerkship - Acute Visual Loss_Student Copy.pdf [4] Senior notes: Ryan Ho Rheumatology.pdf (Section 3.6.1 — Giant Cell Arteritis) [5] Senior notes: Ryan Ho Opthalmology.pdf (Section 3.7.1 — Retinal Artery Occlusion) [6] Senior notes: Ryan Ho Opthalmology.pdf (Section 3.5.1 — Vitreous Haemorrhage) [7] Senior notes: Maksim Medicine Notes.pdf (Section 11.8 — CNS demyelinating diseases) [8] Senior notes: Block A - I keep on bumping into people on my side_ pituitary tumours; hypopituitarism.pdf [9] Lecture slides: 2024 General Clerkship - Acute Visual Loss_Student Copy.pdf (PBL Patient 4) [10] Senior notes: Block A - Rheumatology Interactive Tutorial.pdf (Case 1 — GCA/PMR) [11] Senior notes: Ryan Ho Endocrine.pdf (Section 1.4.1.1 — Graves' Ophthalmopathy) [12] Senior notes: Ryan Ho Endocrine.pdf (Section A — Diabetic Retinopathy)
Differential Diagnosis of Acute Visual Loss
The differential diagnosis of acute visual loss is best approached anatomically — systematically walking along the visual pathway from the front of the eye (ocular media) to the back of the brain (occipital cortex). This is the approach that will serve you best both in exams and on the ward, because the history and examination findings naturally localize the lesion to a specific anatomical compartment.
"List at least six important causes of acute visual loss" — this is directly asked in the GC lecture PBL [1]. Your differential must be organized and systematic, not a random list.
Before jumping into the full differential, let me explain the three key axes that narrow the differential at the bedside, and why each axis works:
Triage Framework: Three Axes of Differentiation
- Why this matters: The optic chiasm is the anatomical watershed. Anything pre-chiasmal (eye, retina, optic nerve) causes unilateral visual loss. Anything at or posterior to the chiasm (chiasm, optic tract, radiations, occipital cortex) causes bilateral or visual field defects that respect the vertical midline.
- Exception: bilateral pre-chiasmal disease can cause bilateral visual loss (e.g., bilateral optic neuritis in NMOSD, bilateral NAION, methanol poisoning) [2][3]
- Why this matters: Pain indicates either inflammation (uveitis, optic neuritis, scleritis, keratitis), raised intraocular pressure (AACG), or ischaemia of pain-sensitive structures (GCA causing headache — though the visual loss itself from AAION is painless). Purely vascular retinal events (CRAO, CRVO, retinal detachment, vitreous haemorrhage) are characteristically painless.
- Why this matters: Transient visual loss (amaurosis fugax) usually indicates transient ischaemia (vascular insufficiency) or neuronal depression (migraine), while persistent visual loss indicates structural damage [4]. Transient events are warning signs — they may herald a permanent event (e.g., amaurosis fugax preceding CRAO).
These cause visual loss by blocking light transmission to the retina. Think of it as putting a frosted glass in front of a projector — the projector (retina, optic nerve) is fine, but the image cannot get through.
| Condition | Key Differentiating Features | Pathophysiological Basis |
|---|---|---|
| Acute angle-closure glaucoma (AACG) | Painful red eye, halos around lights, N/V, mid-dilated fixed pupil, very high IOP, shallow anterior chamber [1] | Pupillary block → iris bowed forward → trabecular meshwork occluded → aqueous cannot drain → IOP rises acutely → corneal endothelial pump overwhelmed → corneal oedema (explains hazy vision and halos); iris sphincter ischaemia (fixed mid-dilated pupil); vagal reflex (N/V) |
| Vitreous haemorrhage | Sudden painless visual loss, floaters/red hue, worse in morning, loss of red reflex [4][5] | Blood in vitreous blocks light. Worse in morning because blood settles on macula overnight when supine. Most common cause = proliferative diabetic retinopathy [5] |
| Keratitis / Corneal ulcer | Painful red eye, photophobia, FB sensation, ± contact lens wear | Corneal infection → inflammatory infiltrate → corneal opacity → blocks light. Contact lens is major risk factor [4] |
| Anterior uveitis / Endophthalmitis | Painful red eye (ciliary flush), photophobia, ± hypopyon | Inflammatory cells and protein ("flare") in the anterior chamber → reduces media clarity. Endophthalmitis = intraocular infection, often post-surgical — ophthalmic emergency |
| Hyphaema | Blood in anterior chamber, usually post-traumatic | Ruptured iris/angle vessels → blood layers in anterior chamber → blocks light if significant |
AACG — Especially Important in Hong Kong
AACG is more common in East Asian populations due to shallower anterior chambers and shorter axial lengths. In any middle-aged or elderly Chinese patient presenting with acute painful visual loss + red eye + nausea/vomiting, AACG should be at the top of your differential. A simple palpation test (comparing firmness of the affected eye vs. the normal eye through closed lids) can give you a clue — the affected globe feels "rock hard." [1]
These cause visual loss by damage to the photoreceptor/neural retinal tissue itself — either through ischaemia (vascular occlusion), detachment (separation from blood supply), or macular pathology.
| Condition | Key Differentiating Features | Pathophysiological Basis |
|---|---|---|
| CRAO | Sudden, profound, painless monocular visual loss (usually HM or worse). RAPD always present. Fundus: cherry-red spot, pale retina, attenuated arteries, ± visible embolus (Hollenhorst plaque) [6] | Embolic occlusion of CRA → inner retina ischaemia → ganglion cell death. Cherry-red spot: thin macula allows choroidal vasculature to show through against the pale ischaemic surrounding retina. Stroke equivalent — carotid disease is the most common cause [6] |
| BRAO | Sudden monocular loss of a specific visual field. Sectoral retinal whitening, embolus commonly seen (~2/3) [6] | Same mechanism as CRAO but limited to a branch artery territory. VA may be preserved if macula is spared |
| CRVO | Sudden painless monocular visual loss (variable severity). Fundus: "blood and thunder" — widespread flame haemorrhages in all 4 quadrants, dilated tortuous veins, cotton wool spots, disc oedema | Thrombotic occlusion of central retinal vein → venous congestion → back-pressure → haemorrhage, oedema. Risk: neovascular glaucoma ("90-day glaucoma") in ischaemic type |
| BRVO | Same as CRVO but limited to one sector; sectoral flame haemorrhages | Same mechanism but in a branch vein territory |
| Retinal detachment | Flashes (photopsia) + floaters as prodrome, then "curtain" or "shadow" across vision. Painless [1][7] | PVD causes traction → retinal tear → liquid vitreous enters subretinal space → neurosensory retina separates from RPE → photoreceptors lose metabolic support. Flashing light = vitreous traction on retina (warning sign for retinal tear) [7] |
| Acute maculopathy (wet AMD) | Central visual loss with metamorphopsia (distortion of straight lines). Peripheral vision preserved. Amsler grid test positive [1] | Choroidal neovascularization → subretinal fluid/blood at the macula → distortion of photoreceptor alignment. The GC PBL Patient 3 describes "a constant black patch directly in the middle of the field of vision" with "distortion for a number of days" — this is classic wet AMD [1] |
| Central serous chorioretinopathy (CSCR) | Central blurring, micropsia (objects appear smaller), often in young stressed males or steroid users | Focal RPE dysfunction → serous detachment of the neurosensory retina at the macula |
Key exam discriminator: CRAO and CRVO are both sudden painless monocular visual loss, but the fundus appearances are completely different. CRAO = pale retina with cherry-red spot. CRVO = "blood and thunder" with widespread haemorrhages. This is a favourite exam question. [6]
These cause visual loss through damage to the optic nerve itself — by inflammation (neuritis), ischaemia (AION), or compression. They share key features: RAPD positive, visual field defects (central scotoma or altitudinal), and colour vision loss (dyschromatopsia).
| Condition | Key Differentiating Features | Pathophysiological Basis |
|---|---|---|
| Optic neuritis | Young patient (20-40y), PAINFUL (worse on eye movement), subacute (hours-days), ↓colour vision disproportionate to ↓VA, RAPD+. Fundus: papillitis (1/3) or normal (retrobulbar neuritis 2/3) [8] | Immune-mediated demyelination → impaired signal conduction. Pain from inflamed nerve swelling within its sheath; eye movement tugs on it (rectus muscles insert near the sheath). Associated with MS, NMOSD, MOG-IgG disease [3][8] |
| AAION (GCA) | Elderly ( > 50y), PAINLESS visual loss (may be preceded by amaurosis fugax), temporal headache, jaw claudication, scalp tenderness, PMR symptoms. ESR characteristically very high. Fundus: chalky white swollen disc [9][10] | Granulomatous arteritis of posterior ciliary arteries → optic nerve head ischaemia/infarction. GCA is a sight-threatening disease — risk of fellow eye involvement if untreated [10] |
| NAION | Elderly ( > 50y), PAINLESS, often noticed on waking ("wake up with visual loss"), altitudinal visual field defect. Fundus: hyperaemic swollen disc (not as pale as AAION) | Small-vessel ischaemia in the optic nerve head watershed zone. Occurs in "disc at risk" (small cup-to-disc ratio). Nocturnal hypotension reduces perfusion → compartment-like ischaemia |
| Compressive optic neuropathy | Gradual onset usually, but pituitary apoplexy causes acute onset. Pituitary tumour → bitemporal hemianopia [11]. Graves' ophthalmopathy → apical crowding → ↓colour vision, RAPD+ [12] | Mass lesion compresses optic nerve or chiasm → axonal damage |
| Papilloedema | Bilateral disc oedema, enlarged blind spot, transient visual obscurations (seconds). VA initially preserved | ↑ICP → impaired axoplasmic flow → disc swelling. TVOs are brief (seconds), bilateral, worse with postural change [4] |
| Traumatic optic neuropathy | History of trauma (direct or indirect injury to optic canal) | Shearing forces transmitted to the optic nerve within the optic canal → axonal injury ± vascular compromise |
Optic Neuritis vs AION — The Classic Exam Comparison
Both cause acute monocular visual loss with RAPD. Students frequently confuse them. Remember:
| Feature | Optic Neuritis | AAION (GCA) | NAION |
|---|---|---|---|
| Age | 20-40y | > 50y | > 50y |
| Pain | Yes (on eye movement) | Painless (headache is separate) | Painless |
| Onset | Subacute (days) | Sudden | Sudden (often on waking) |
| Colour vision | Disproportionately ↓ | ↓ | ↓ |
| Disc | Papillitis or normal | Chalky white, swollen | Hyperaemic, swollen |
| Association | MS, NMOSD | PMR, ↑↑ESR | HTN, DM, small disc |
| Treatment | IV methylprednisolone | Urgent high-dose steroids | None proven |
These cause bilateral visual field defects that respect the vertical midline. They do not cause RAPD (because both eyes' afferent signals have mixed posterior to the chiasm).
| Condition | Key Differentiating Features | Pathophysiological Basis |
|---|---|---|
| Pituitary apoplexy | Acute headache, bitemporal hemianopia, ophthalmoplegia (CN III, IV, VI), altered consciousness. Neurosurgical emergency [11] | Acute haemorrhage/infarction of pituitary adenoma → sudden expansion → compression of optic chiasm (bitemporal hemianopia) and cavernous sinus (CN III, IV, VI palsies) |
| Occipital lobe stroke (PCA territory) | Homonymous hemianopia (contralateral to lesion), intact pupillary reflexes, ± other neurological deficits [2] | PCA infarction → visual cortex damage → contralateral homonymous hemianopia. Pupillary reflexes preserved because the pupillary pathway is subcortical (pretectal nuclei) |
| Bilateral occipital infarction | Cortical blindness — bilateral visual loss with intact pupillary reflexes. Patient may deny blindness (Anton's syndrome) [2] | Bilateral PCA infarction → complete visual cortex destruction. Pupillary reflex preserved. Anton's syndrome = anosognosia (unawareness of blindness, patient confabulates vision) |
Transient visual loss is critical because it may herald a permanent, catastrophic event. [4]
| Condition | Key Differentiating Features | Pathophysiological Basis |
|---|---|---|
| Amaurosis fugax (retinal TIA) | Painless, monocular, lasts seconds-minutes. "Curtain down" description. Causes: carotid atherosclerosis (embolic), GCA, cardiogenic embolism [4] | Transient embolic occlusion of CRA or its branches → transient retinal ischaemia → spontaneous resolution when embolus passes or fragments. Warning sign for CRAO or stroke — demands urgent vascular workup |
| Retinal migraine | Onset usually < 40y, positive phenomena (scintillating scotomas) or negative phenomena, lasting 5-60 min, accompanied by or followed ≤60 min by migraine headache [4] | Retinal vasospasm and occipital cortical spreading depression |
| Papilloedema-related TVOs | Brief (seconds), bilateral, unilateral, or altitudinal. Worse with posture change. Look for headache and bilateral disc swelling [4] | Transient ischaemia of swollen optic disc axons with postural change or Valsalva. The swollen disc is vulnerable to transient hypoperfusion |
| Condition | Key Differentiating Features | Pathophysiological Basis |
|---|---|---|
| Methanol poisoning | Bilateral visual loss, "snowstorm-like" blurry vision, metabolic acidosis (↑anion gap, ↑osmolal gap). Fundoscopy: disc hyperaemia or pallor [13] | Methanol → formic acid (via alcohol dehydrogenase → formaldehyde → formic acid). Formic acid inhibits cytochrome c oxidase in mitochondria → tissue hypoxia → selective toxicity to optic nerve and retina (high metabolic demand). Sources: fake wine, antifreeze, windshield washer fluid |
| Hyperviscosity syndrome | Visual symptoms (amaurosis fugax, blurred vision), headache, mucosal bleeding. Causes: polycythaemia vera (PV), leukaemia (leukostasis), Waldenström's [14][15] | ↑Blood viscosity → sluggish retinal blood flow → relative retinal ischaemia. In PV: transient visual symptoms including amaurosis fugax, scintillating scotoma, ophthalmic migraine [14]. In leukostasis: central retinal vein thrombosis [15] |
| Malignant hypertension | BP usually > 200/120, papilloedema, retinal haemorrhages and exudates, visual disturbances including transient blindness [16] | Severely ↑BP → breakdown of retinal vascular autoregulation → fibrinoid necrosis → haemorrhages, exudates, cotton wool spots, papilloedema. Can also cause hypertensive encephalopathy with cortical visual disturbance |
| Functional (non-organic) visual loss | Inconsistent examination findings (e.g., VA that varies with testing method, intact opticokinetic nystagmus, normal pupillary responses, normal fundus). Diagnosis of exclusion | No structural pathology. Previously called "conversion disorder" or "hysteria." Must exclude organic disease before making this diagnosis [2] |
| Endophthalmitis | Painful red eye, severe visual loss, hypopyon, usually post-operative or post-traumatic | Intraocular infection (bacterial > fungal) → severe inflammation → media opacity + retinal destruction. Ophthalmic emergency requiring urgent intravitreal antibiotics ± vitrectomy |
| Diabetic complications | Sudden visual loss from vitreous haemorrhage, tractional retinal detachment, rubeotic glaucoma, or macular oedema [17] | Chronic hyperglycaemia → retinal microangiopathy → ischaemia → neovascularization → complications. Visual loss from DR is secondary to macular oedema (NPDR), vitreous haemorrhage (PDR), tractional retinal detachment (PDR), or neovascular glaucoma (PDR) [17] |
| Infective endocarditis | Roth spots on fundoscopy (retinal haemorrhages with pale centres), septic emboli to retinal vessels | Septic emboli from vegetations → retinal microinfarction [18] |
This is the table you should be able to reconstruct in an exam:
| Presentation | Painful? | RAPD? | Key Fundoscopic Findings | Diagnosis |
|---|---|---|---|---|
| Sudden profound painless monocular visual loss | No | Always | Cherry-red spot, pale retina, attenuated arteries | CRAO |
| Sudden monocular VF loss | No | ± | Sectoral whitening, visible embolus | BRAO |
| Sudden painless monocular visual loss | No | ± | "Blood and thunder" — widespread haemorrhages, tortuous veins | CRVO |
| Painful monocular visual loss, young patient | Yes | Yes | Papillitis (1/3) or normal (2/3) | Optic neuritis |
| Sudden painless monocular visual loss, elderly | No | Yes | Chalky white swollen disc | AAION (GCA) |
| Sudden painless monocular visual loss, elderly, on waking | No | Yes | Hyperaemic swollen disc | NAION |
| Floaters + flashes → "curtain" across vision | No | ± | Elevated retina, ± retinal tear | Retinal detachment |
| Sudden painless visual loss, floaters, worse in AM | No | No | Loss of red reflex, blood in vitreous | Vitreous haemorrhage |
| Central scotoma + metamorphopsia | No | No | Subretinal fluid/blood at macula | Wet AMD |
| Painful red eye, halos, N/V, mid-dilated fixed pupil | Yes | No | Corneal oedema, shallow AC, ↑↑IOP | AACG |
| Transient monocular visual loss, seconds-minutes | No | No (between attacks) | Usually normal between attacks | Amaurosis fugax |
| Bitemporal hemianopia ± headache ± ophthalmoplegia | ± | No | ± optic atrophy | Pituitary tumour / apoplexy |
| Contralateral homonymous hemianopia | No | No | Normal fundi | Occipital stroke |
| Bilateral visual loss + metabolic acidosis | ± | ± | Disc hyperaemia or pallor | Methanol poisoning |
The following key decision points allow systematic narrowing of the differential:
Step 1: Is it unilateral or bilateral?
- Unilateral → pre-chiasmal (eye or optic nerve)
- Bilateral (or bitemporal/homonymous VF defect) → chiasmal or retrochiasmal
Step 2: Is there pain?
- Painful → AACG, optic neuritis, keratitis, uveitis, endophthalmitis, trauma
- Painless → vascular (CRAO, CRVO, AION), retinal detachment, vitreous haemorrhage, maculopathy
Step 3: Check RAPD
- RAPD present → optic nerve (optic neuritis, AION) or extensive retinal disease (CRAO, extensive RD)
- RAPD absent with ↓VA → media opacity, macular disease, refractive error, functional
Step 4: Look at the fundus
- Cherry-red spot → CRAO
- "Blood and thunder" → CRVO
- Pale swollen disc → AAION
- Hyperaemic swollen disc → NAION, papillitis
- Bilateral disc swelling → papilloedema
- Elevated retina → retinal detachment
- Subretinal fluid/blood at macula → wet AMD
- Loss of red reflex → vitreous haemorrhage
- Normal fundus → retrobulbar optic neuritis, occipital stroke, functional
Step 5: Age-based thinking
- Young (20-40y) → optic neuritis (MS, NMOSD), CSCR, retinal detachment (if myopic)
- Middle-aged → CRVO, RD, wet AMD, AACG
- Elderly ( > 50y) → CRAO, AAION (GCA), NAION, wet AMD, occipital stroke
Step 6: Never forget to ask about GCA symptoms in any elderly patient
- Temporal headache, jaw claudication, scalp tenderness, PMR symptoms, constitutional symptoms, amaurosis fugax [9][10]
GC PBL Cases — Diagnostic Patterns to Recognize
The GC 121 Acute Visual Loss PBL [1] presents several classic patterns:
- Patient 1: VA 6/60 OD, 6/9 OS, moderate right RAPD, fundus image shown → likely CRAO or CRVO or AION — the RAPD and fundus findings will clinch it. Systemic investigations indicated (carotid imaging, ECG, echocardiography if CRAO; ESR/CRP if AION in elderly)
- Patient 3: VA 6/60 OD, central scotoma with metamorphopsia, distortion for days, "black patch in the middle" with peripheral vision preserved, Amsler grid positive → wet AMD (acute maculopathy). Metamorphopsia + central scotoma = macular pathology
- Patient 4: 63-year-old man with mobile translucent strands "like a cobweb" and flickering light, VA 6/6 both eyes → Posterior vitreous detachment (PVD) with risk of retinal tear. Good VA does NOT provide reassurance — the macula may be unaffected but a peripheral retinal tear may be present. The flickering light signifies vitreous traction on the retina. Needs urgent dilated fundoscopy
| Factor | Relevance |
|---|---|
| AACG | Higher prevalence in East Asians — should always be considered in acute painful visual loss [1] |
| NMOSD | More common in Asian populations than MS. Anti-AQP4 antibodies. Tends to cause more severe/bilateral optic neuritis [3][8] |
| Diabetic retinopathy | Hong Kong has a high prevalence of DM. Vitreous haemorrhage from PDR is a common cause of acute painless visual loss [5][17] |
| GCA | Less common in Asian populations than Caucasians, but must still be excluded in any elderly patient with acute visual loss + suspicious symptoms [9][10] |
| Methanol poisoning | Rare but important — outbreaks have occurred in Asia. "Snowstorm-like" blurry vision + metabolic acidosis (↑anion gap, ↑osmolal gap) [13] |
High Yield Summary — Differential Diagnosis of Acute Visual Loss
- Organize the differential anatomically: ocular media → retina → optic nerve → chiasm/retrochiasmal → transient → systemic
- Three key axes for differentiation: laterality (unilateral vs bilateral), pain (painful vs painless), duration (transient vs persistent)
- RAPD localizes to optic nerve or extensive retinal disease — absent in media opacity, macular disease, refractive error, retrochiasmal lesions
- Fundoscopy is the single most discriminating examination: cherry-red spot = CRAO, "blood and thunder" = CRVO, pale swollen disc = AAION, elevated retina = RD, loss of red reflex = vitreous haemorrhage
- CRAO = stroke equivalent — always investigate for carotid disease, cardiac source, vascular risk factors
- GCA must be excluded in ANY patient > 50y with acute visual loss — ask about temporal headache, jaw claudication, scalp tenderness, PMR symptoms, check ESR/CRP urgently
- Optic neuritis: young, painful (eye movement), subacute, ↓colour vision, RAPD+, associated with MS/NMOSD/MOG
- AACG: more common in East Asians (Hong Kong relevance), painful red eye, halos, N/V, mid-dilated fixed pupil, ↑↑IOP
- New floaters + flashes with good VA does NOT provide reassurance — must urgently exclude retinal tear/detachment
- Methanol: bilateral visual loss + "snowstorm" vision + metabolic acidosis (↑AG, ↑OG) — formic acid inhibits cytochrome c oxidase → optic nerve toxicity
Active Recall - Differential Diagnosis of Acute Visual Loss
References
[1] Lecture slides: 2024 General Clerkship - Acute Visual Loss_Student Copy.pdf [2] Senior notes: Ryan Ho Neurology.pdf (Section 2 — Optic Nerve, CN II) [3] Senior notes: Maksim Medicine Notes.pdf (Section 11.8 — CNS demyelinating diseases) [4] Senior notes: Ryan Ho Opthalmology.pdf (Section 3.1 — Approach to Acute Visual Loss) [5] Senior notes: Ryan Ho Opthalmology.pdf (Section 3.5.1 — Vitreous Haemorrhage) [6] Senior notes: Ryan Ho Opthalmology.pdf (Section 3.7.1 — Retinal Artery Occlusion) [7] Lecture slides: 2024 General Clerkship - Acute Visual Loss_Student Copy.pdf (PBL Patient 4) [8] Senior notes: Ryan Ho Opthalmology.pdf (Section 4.3.3 — Optic Neuritis) [9] Senior notes: Ryan Ho Rheumatology.pdf (Section 3.6.1 — Giant Cell Arteritis) [10] Senior notes: Block A - Rheumatology Interactive Tutorial.pdf (Case 1 — GCA/PMR) [11] Senior notes: Block A - I keep on bumping into people on my side_ pituitary tumours; hypopituitarism.pdf [12] Senior notes: Ryan Ho Endocrine.pdf (Section 1.4.1.1 — Graves' Ophthalmopathy) [13] Senior notes: Ryan Ho Chemical Path.pdf (Section D — Methanol) [14] Senior notes: Ryan Ho Haemtology.pdf (Section 3.3.2.1 — Polycythaemia Vera) [15] Senior notes: Block A - High white cell count_ acute and chronic leukaemia; bone marrow transplantation; immunogenetics.pdf (Leukostasis) [16] Senior notes: Block A - High blood pressure_ hypertension.pdf (Malignant hypertension) [17] Senior notes: Ryan Ho Endocrine.pdf (Section A — Diabetic Retinopathy) [18] Senior notes: Block A - Fever and a murmur_ Valvular heart diseases; Infective endocarditis.pdf
Conceptual Framework: Why We Investigate in Acute Visual Loss
Acute visual loss is a symptom, not a diagnosis. The purpose of investigation is threefold:
- Confirm the diagnosis (e.g., fundoscopy findings, IOP measurement, imaging)
- Identify the underlying aetiology (e.g., carotid Doppler for CRAO, ESR/CRP for GCA, MRI brain for MS)
- Guide management urgency (e.g., GCA must be treated immediately — do not wait for biopsy; CRAO is a stroke equivalent requiring vascular workup)
There is no single "diagnostic criterion" for "acute visual loss" as a whole — rather, each underlying cause has its own diagnostic approach. However, the systematic clinical evaluation at the bedside is itself the primary diagnostic tool, and most causes of acute visual loss are diagnosed clinically with supporting investigations.
1. Diagnostic Criteria for Key Causes
GCA deserves its own criteria because it is the most time-critical diagnosis — missing it risks bilateral permanent blindness.
ACR Classification Criteria for GCA (≥3 out of 5): [19][20]
Mnemonic: "BATHE"
- Biopsy evidence: necrotizing arteritis with mononuclear cells or multinucleated giant cells (granuloma)
- Age ≥ 50 years
- Tenderness or decreased pulsation of temporal artery
- Headache: new onset, localized
- ESR > 50 mm/h
Critical Exam Point — GCA Diagnosis
For visual symptoms, do NOT wait for biopsy results → start empirical high-dose steroids immediately upon clinical suspicion. The biopsy may show false negatives due to skip lesions (patchy, non-contiguous inflammation along the artery). Treatment must not be delayed because the risk of fellow eye involvement is up to 50% if untreated. [9][19][20]
Clinical diagnosis is made when: [8]
- Unilateral ↓VA
- Pain with eye movement and/or periorbital pain
- RAPD positive (if the other eye is uninvolved — always occurs)
- Dyschromatopsia (↓colour vision disproportionate to ↓VA)
- VF: typically central, centrocaecal, or paracentral scotomas
No formal "diagnostic criteria" exist in the way ACR criteria exist for GCA. It is a clinical diagnosis, supported by MRI (which also evaluates for MS).
The classification of diabetic retinopathy serves as both a staging system and a diagnostic framework: [17][21]
| Stage | Key Findings | Significance |
|---|---|---|
| Mild NPDR | ≥1 microaneurysm (earliest sign) | Earliest detectable change |
| Moderate NPDR | Multiple microaneurysms, dot-and-blot haemorrhages, venous beading, ± cotton wool spots | Progressive microvascular damage |
| Severe NPDR | 4-2-1 rule: diffuse haemorrhage + microaneurysms in 4 quadrants, venous beading in ≥2 quadrants, IRMA in ≥1 quadrant | 52–75% will progress to PDR |
| Proliferative DR | Retinal neovascularization, vitreous haemorrhage, pre-retinal fibrosis, rubeosis iridis | High risk of acute visual loss from vitreous haemorrhage, tractional RD, rubeotic glaucoma |
| Diabetic macular oedema | Retinal thickening involving macula — diagnosed by slit-lamp biomicroscopy or OCT (not fundoscopy alone) | Commonest cause of vision loss in DM |
These are clinical diagnoses based on history + fundoscopic findings. There are no formal "criteria" — the diagnosis is made when the characteristic clinical picture is present:
- CRAO: sudden profound painless monocular visual loss + cherry-red spot + pale retina + attenuated arteries + RAPD [6]
- CRVO: sudden painless monocular visual loss + widespread flame haemorrhages in all 4 quadrants + dilated tortuous veins + disc oedema
Once the ocular diagnosis is made, the investigation shifts to identifying the underlying cause (see below).
Clinical diagnosis confirmed by IOP measurement (typically > 40–60 mmHg) combined with:
- Shallow anterior chamber on slit lamp
- Corneal oedema
- Mid-dilated fixed pupil
- Gonioscopy showing closed angle (definitive confirmation — but often deferred to after acute management)
The following algorithm represents the systematic approach to a patient presenting with acute visual loss:
Step-by-Step Explanation of the Algorithm
Step 1: History — This is where you generate your differential. The three axes (laterality, pain, duration) immediately narrow the possibilities. The associated symptoms and risk factors further refine.
Step 2: Bedside Examination — Five core components, each of which provides critical localizing information:
| Examination | What It Tells You | Why |
|---|---|---|
| Visual acuity | Severity of visual loss; whether refractive (improves with pinhole) or pathological | Pinhole eliminates refractive error by reducing the aperture to a point source — if VA improves with pinhole, the problem is optical, not neurological [2] |
| RAPD | Unilateral optic nerve or extensive retinal lesion | The swinging flashlight test compares the afferent signal strength between the two eyes. A weaker signal from one eye = RAPD on that side [2][6] |
| Confrontation VF | Localizes: central scotoma (macular/ON), altitudinal (AION), "curtain" (RD), hemianopia (retrochiasmal) | Different parts of the visual pathway serve different parts of the visual field |
| Anterior segment | Identifies media causes: AACG (shallow AC, corneal oedema, fixed pupil), uveitis (cells/flare), keratitis (corneal opacity) | Direct inspection of the structures light must pass through |
| Fundoscopy | The single most discriminating examination — directly visualizes the retina and optic disc | Each cause has a characteristic fundoscopic "signature" (see table below) |
Step 3: Targeted Investigations — Once the clinical diagnosis is formed, investigations are directed at confirming the diagnosis and identifying the underlying cause.
3. Investigation Modalities — Key Findings and Interpretations
3.1 Bedside / Office Investigations
- The most useful bedside test in acute visual loss [1]
- Performed in a dim room, asking the patient to fixate on a distant target
- Swing a bright light from one eye to the other, holding for ~3 seconds on each eye
- Positive RAPD: the affected pupil dilates when the light swings to it (because the brain perceives the light as "dimmer" compared to what it just received from the normal eye)
- RAPD present in: CRAO, CRVO (extensive/ischaemic), optic neuritis, AION, compressive optic neuropathy, extensive retinal detachment
- RAPD absent in: media opacity (cataract, vitreous haemorrhage), macular disease, refractive error, retrochiasmal lesions [2][6][8]
- Patient sits 1m away, covers one eye, fixates on examiner's nose
- Examiner wiggles fingers in each quadrant — patient reports when they see movement
- Why this works: Each quadrant of the visual field maps to a specific part of the visual pathway. A defect in one quadrant localizes the lesion.
- More formal testing: Amsler grid (a grid of horizontal and vertical lines with a central fixation dot) — detects central scotoma and metamorphopsia (distortion of lines), highly sensitive for macular pathology [1]
The GC PBL Patient 3 describes central scotoma with metamorphopsia detected on Amsler grid → classic for wet AMD. [1]
- Goldmann applanation tonometry (gold standard, done at slit lamp)
- Non-contact tonometry (air-puff) — screening
- Rough bedside estimate: palpate globe through closed eyelids (compare both sides) — in AACG the affected eye feels "rock hard"
- Normal: 10–21 mmHg
- AACG: typically > 40–60 mmHg
- Examines cornea, anterior chamber, lens, and anterior vitreous in magnified detail
- Key findings:
| Finding | Condition | Explanation |
|---|---|---|
| Corneal oedema | AACG | ↑IOP overwhelms endothelial pump |
| Cells and flare in AC | Uveitis | Inflammatory cells + protein leaking through broken blood-aqueous barrier |
| Hypopyon | Endophthalmitis, severe uveitis | Layered inflammatory cells settling by gravity |
| Shallow AC | AACG | Predisposing anatomy; iris pushed forward |
| RBCs in anterior vitreous | Vitreous haemorrhage | Blood from posterior segment migrating anteriorly [5] |
| Rubeosis iridis | PDR, ischaemic CRVO | Neovascularization of iris driven by VEGF from ischaemic retina [17] |
The single most important investigation in acute visual loss — it is both a bedside test and a diagnostic investigation.
| Fundoscopic Finding | Diagnosis | Interpretation |
|---|---|---|
| Cherry-red spot + pale retina + attenuated arteries ± visible embolus | CRAO | Inner retina is ischaemic (white/opaque); thin fovea allows choroidal red to show through [6] |
| Sectoral retinal whitening ± embolus | BRAO | Same as CRAO but in a branch territory [6] |
| Widespread flame haemorrhages, dilated tortuous veins, CWS, disc oedema | CRVO | Venous congestion → back-pressure → haemorrhage and oedema |
| Chalky white swollen disc with haemorrhages | AAION (GCA) | Posterior ciliary artery occlusion → optic nerve head infarction [9] |
| Hyperaemic swollen disc, sectoral oedema | NAION | Watershed ischaemia; less severe than AAION |
| Papillitis (hyperaemic swollen disc with distended veins) | Optic neuritis (anterior) | Inflammatory oedema of the disc [8] |
| Normal disc | Retrobulbar optic neuritis | Inflammation is behind the globe — "the patient sees nothing and the doctor sees nothing" [8] |
| Bilateral disc oedema | Papilloedema | ↑ICP → impaired axoplasmic flow |
| Loss of red reflex, blood obscuring retinal view | Vitreous haemorrhage | Blood in vitreous cavity blocks the view [5] |
| Elevated/detached retina, ± retinal tear | Retinal detachment | Separation of neurosensory retina from RPE |
| Subretinal fluid/blood at macula | Wet AMD | Choroidal neovascularization leaking under the macula |
| Microaneurysms, dot-and-blot, neovascularization | Diabetic retinopathy | Retinal microangiopathy ± neovascularization [17] |
| Disc hyperaemia or pallor | Methanol poisoning | Formic acid → cytochrome oxidase inhibition → optic nerve toxicity [13] |
| Dilated, segmented, tortuous "sausage link" retinal veins ± haemorrhage, exudate, papilloedema | Hyperviscosity syndrome | ↑Blood viscosity → sluggish retinal blood flow [22] |
| Retinal haemorrhages with pale centres (Roth spots) | Infective endocarditis | Septic microemboli → retinal infarcts with surrounding haemorrhage [18] |
| Retinal artery narrowing, AV nipping, flame haemorrhages, CWS | Hypertensive retinopathy | Chronic HTN → arteriosclerosis; acute/malignant HTN → fibrinoid necrosis [23] |
3.2 Blood Investigations
Blood tests in acute visual loss serve to identify the underlying cause and guide management.
Essential in any elderly patient ( > 50y) with acute visual loss to exclude GCA. [9][19][20]
| Test | Significance | Interpretation |
|---|---|---|
| ESR | Characteristically very high in GCA (often > 100 mm/h) | ESR > 50 mm/h is one of the ACR diagnostic criteria for GCA [20]. However, a normal ESR does not exclude GCA (~4% of biopsy-proven GCA have normal ESR) |
| CRP | More sensitive than ESR for acute inflammation | Usually markedly elevated in GCA. Combined ESR + CRP provides high sensitivity |
For GCA: check ESR and CRP urgently in any patient > 50y with acute visual loss ± headache ± jaw claudication ± scalp tenderness. Do NOT wait for results before starting steroids if clinical suspicion is high. [9][19]
| Finding | Significance |
|---|---|
| NcNc anaemia | GCA-associated anaemia of chronic disease; also seen in malignancy |
| Reactive thrombocytosis | GCA (platelet count often elevated as acute phase reactant) [9][20] |
| Polycythaemia (↑Hb/Hct) | Polycythaemia vera → hyperviscosity → retinal vascular symptoms [14] |
| Leukocytosis with blasts | Leukaemia → leukostasis → retinal vein thrombosis [15] |
| Pancytopenia | Myeloproliferative/infiltrative disorder |
These are critical in retinal vascular occlusions (CRAO, CRVO) because they share risk factors with stroke and systemic vascular disease.
| Test | Relevance |
|---|---|
| Blood glucose / HbA1c | DM screening — risk factor for retinal vascular disease and diabetic retinopathy [17][21] |
| Fasting lipid profile | Hyperlipidaemia — atherosclerotic risk factor |
| Renal function (RFT) | Chronic kidney disease — vascular risk, also relevant if contrast imaging needed |
| Clotting profile (PT, APTT) | Coagulopathy screen; also needed before temporal artery biopsy |
| Thrombophilia screen | In young patients with retinal vascular occlusion without obvious risk factors: antiphospholipid antibodies, protein C, protein S, antithrombin III, Factor V Leiden |
| Test | When | Why |
|---|---|---|
| Anti-AQP4 antibodies (aquaporin-4) | Suspected NMOSD | Specific for NMOSD — separates it from MS [3][8] |
| Anti-MOG antibodies | Suspected MOG-IgG disease | Identifies MOG-antibody disease (distinct from MS and NMOSD) |
| TRAb (TSH receptor antibodies) | Suspected Graves' ophthalmopathy | Correlates with clinical severity of Graves' orbitopathy [12] |
| TFT (thyroid function tests) | Suspected Graves' ophthalmopathy | Assess underlying thyroid condition [12] |
| ABG, serum osmolality, methanol level | Suspected methanol poisoning | Metabolic acidosis (↑anion gap, ↑osmolal gap). Osmolal gap > 25 specific for toxic alcohol ingestion [13] |
3.3 Imaging Investigations
- What it is: Non-invasive, cross-sectional imaging of the retina using near-infrared light (analogous to ultrasound but using light instead of sound). Provides micron-resolution images of retinal layers.
- Why it matters in acute visual loss:
| Application | Finding | Diagnosis |
|---|---|---|
| Macular oedema | ↑Retinal thickness, intraretinal/subretinal fluid | Diabetic macular oedema, CRVO-related macular oedema [17] |
| Wet AMD | Subretinal/sub-RPE fluid, choroidal neovascular membrane | Wet AMD |
| CSCR | Focal neurosensory detachment at macula with intact RPE | Central serous chorioretinopathy |
| Retinal detachment | Separation of neurosensory retina from RPE | Confirms and characterizes retinal detachment |
| Optic disc oedema | ↑Retinal nerve fibre layer thickness | Papilloedema, papillitis, AION |
Diabetic macular oedema can only be diagnosed by slit-lamp retinal biomicroscopy (measurement of retinal thickness) or indirect ophthalmoscopy — fundoscopy may be normal or only show mild NPDR [17]. In modern practice, OCT has largely replaced clinical biomicroscopy for this purpose.
- What it is: IV fluorescein dye is injected; sequential photographs of the retina are taken as the dye transits through the retinal and choroidal vasculature
- Why it matters:
| Application | Finding | Diagnosis |
|---|---|---|
| Retinal artery occlusion | Delayed/absent arterial filling, ± embolus | CRAO/BRAO |
| Retinal vein occlusion | Delayed venous filling, hyperfluorescence from leakage, non-perfusion areas | CRVO/BRVO |
| Diabetic retinopathy | Microaneurysms, capillary non-perfusion, neovascularization (leak on FFA) | Stages DMR, guides treatment |
| Wet AMD | Choroidal neovascular membrane showing early hyperfluorescence with late leakage | Confirms CNV, guides anti-VEGF therapy |
| CSCR | Focal "smokestack" or "inkblot" leakage at RPE level | Central serous chorioretinopathy |
- When to use: When the fundus cannot be visualized (e.g., dense vitreous haemorrhage, dense cataract)
- Key findings:
| Finding | Diagnosis |
|---|---|
| Vitreous echoes + posterior vitreous membrane | Vitreous haemorrhage ± PVD [5] |
| Retinal membrane attached at disc and ora serrata | Retinal detachment |
| Intraocular mass | Tumour (e.g., choroidal melanoma) |
| Foreign body | Intraocular foreign body (IOFB) in trauma |
Ocular USG is especially important when vitreous haemorrhage obscures the fundus — it can identify associated PVD, retinal tears/detachment, tumours, and IOFB [5]
| Indication | Findings | Interpretation |
|---|---|---|
| Optic neuritis (suspected MS) | T2/FLAIR hyperintense white matter lesions disseminated in space and time; optic nerve enhancement on contrast | Supports MS diagnosis (McDonald criteria require dissemination in space and time) |
| NMOSD | Longitudinally extensive optic nerve lesion (involving > 50% of optic nerve length); ± spinal cord lesion > 3 vertebral segments | Distinguishes NMOSD from MS (MS lesions tend to be shorter) |
| Pituitary apoplexy | Enlarged pituitary with haemorrhage/infarction on T1 (hyperintense if haemorrhagic); compression of optic chiasm | Neurosurgical emergency — may need urgent decompression [11] |
| Compressive optic neuropathy | Mass lesion (meningioma, pituitary tumour) compressing optic nerve or chiasm | Identifies the cause and guides surgical planning |
| Posterior circulation stroke | DWI restriction in occipital lobe | MRI is more sensitive than CT for early ischaemic stroke (86-100% vs 48% sensitivity < 1 day) [24] |
| Graves' ophthalmopathy | Tendon-sparing EOM enlargement; apical crowding | Assesses risk of ON compression [12] |
MRI is superior to CT for detecting early ischaemic stroke, optic nerve lesions, and posterior fossa pathology. However, CT is faster and more available, and is the first-line imaging in suspected acute stroke to exclude haemorrhage. [24][25]
| Indication | Findings | Interpretation |
|---|---|---|
| Suspected stroke | Hypodense area (ischaemic infarct) or hyperdense area (haemorrhage) | Mainstay of imaging in acute stroke — differentiates ischaemic from haemorrhagic [24][25] |
| Pituitary apoplexy | Enlarged pituitary with haemorrhage | May miss small lesions — MRI preferred if available |
| Raised ICP | Hydrocephalus, mass lesion, midline shift | Explains bilateral papilloedema |
| Indication | Findings | Interpretation |
|---|---|---|
| Graves' ophthalmopathy | Tendon-sparing EOM enlargement (IR > MR > SR > LR), apical crowding, increased orbital fat [12] | Assesses severity and risk of compressive optic neuropathy |
| Orbital cellulitis/abscess | Orbital soft tissue enhancement, subperiosteal collection | Guides drainage if needed |
| Orbital tumour | Mass lesion in orbit | Identifies cause of compressive optic neuropathy |
CRAO is a stroke equivalent — the same vascular workup done for a TIA/stroke is indicated. [6]
GC PBL Patient 1 asks: "What systemic investigations are indicated in this patient?" — the answer is the vascular workup below. [1]
| Investigation | Rationale | Key Findings |
|---|---|---|
| Carotid Doppler ultrasonography | Carotid artery atherosclerosis is the most common cause of CRAO [6] | Stenosis > 50% or plaque with irregular surface → high embolic risk |
| ECG | Screen for AF (cardioembolic source) | AF, prior MI, LVH |
| Echocardiography (TTE ± TOE) | Identify cardiogenic embolic source | Valvular vegetations (endocarditis), intracardiac thrombus, PFO with paradoxical embolism. TOE is more sensitive for valvular vegetations and left atrial appendage thrombus |
| CT/MR angiography | Assess aortic arch and cervicocranial vessels | Atherosclerotic stenosis, dissection |
Vascular Workup in CRAO — Think Like a Stroke Physician
A patient with CRAO needs the exact same workup as a patient with a TIA: carotid Doppler, ECG (for AF), echocardiography (for cardiac embolic source), and vascular risk factor blood tests (glucose, lipids, HbA1c). In younger patients without obvious risk factors, consider thrombophilia screen and vasculitis screen (including GCA if > 50y). [1][6]
3.5 Special Investigations
- Gold standard for confirming GCA [9][19][20]
- Findings: panarteritis with mixed infiltrates (lymphocytes, plasma cells, macrophages), fragmentation of internal elastic lamina, necrosis of media ± giant cells (not necessary for diagnosis) [20]
- Must be ordered urgently ( < 24–48 hours) — delay risks permanent visual impairment [20]
- False negatives occur due to skip lesions (patchy, non-contiguous inflammation) — a negative biopsy does not exclude GCA if clinical suspicion is high [19]
- Biopsy should ideally be ≥1 cm in length and performed on the clinically affected side [19]
- Non-invasive alternative/adjunct to biopsy [19]
- Key finding: "halo sign" — hypoechoic circumferential wall thickening around the temporal artery representing perivascular oedema/inflammation
- Can also assess other H&N and lower limb vessels for large vessel involvement
- Definitive test for confirming angle closure in AACG
- Uses a special contact lens with mirrors to visualize the drainage angle
- Usually performed after acute IOP has been lowered (the oedematous cornea can make visualization difficult during the acute attack)
| Type | Indication | Key Findings |
|---|---|---|
| Humphrey visual field (automated) | All optic nerve and chiasmal lesions, glaucoma | Central scotoma (ON), altitudinal defect (AION), bitemporal hemianopia (chiasm), arcuate scotoma (glaucoma) |
| Goldmann perimetry | Retinal detachment, peripheral field loss, malingering | Maps full visual field including far periphery |
| Condition | Key Bedside Findings | Key Investigations | Interpretation |
|---|---|---|---|
| CRAO | ↓↓VA, RAPD+, cherry-red spot | Carotid Doppler, ECG, Echo, ESR/CRP (r/o GCA if > 50y), lipids, glucose [1][6] | Stroke equivalent workup |
| CRVO | ↓VA, RAPD±, "blood and thunder" fundus | FFA (assess ischaemia vs non-ischaemic), OCT (macular oedema), BP, glucose, lipids, CBC (r/o hyperviscosity) | Ischaemic type → risk of NVG |
| AAION (GCA) | ↓↓VA, RAPD+, pale swollen disc | ESR, CRP (urgently), CBC, temporal artery USG, temporal artery biopsy [9][19][20] | Start steroids before results |
| Optic neuritis | ↓VA, RAPD+, pain on eye movement, ↓colour vision | MRI brain + orbits with gadolinium (for MS/NMOSD), anti-AQP4, anti-MOG [8] | T2 hyperintense lesions support MS |
| AACG | ↓VA, painful red eye, mid-dilated fixed pupil, corneal oedema | IOP (tonometry), slit-lamp (shallow AC), gonioscopy (after acute Mx) | IOP > 40–60 mmHg diagnostic |
| Vitreous haemorrhage | ↓VA (variable), loss of red reflex | B-scan USG (if fundus not visible), assess for DR/tear/RD [5] | Identifies cause if fundus obscured |
| Retinal detachment | "Curtain" VF loss, elevated retina on fundoscopy | Dilated fundoscopy (urgent), B-scan USG if media opacity | Identify tear location for surgery |
| Wet AMD | Central scotoma, metamorphopsia, Amsler grid+ | OCT (subretinal fluid/CNV), FFA (leakage pattern) | Guides anti-VEGF treatment |
| Methanol | Bilateral ↓VA, "snowstorm" vision, metabolic acidosis | ABG, serum osmolality, anion gap, osmolal gap, methanol level [13] | ↑AG + ↑OG → toxic alcohol |
| Occipital stroke | Homonymous hemianopia, normal pupils | NCCT brain (urgent), MRI brain (DWI), CT/MR angiography [24][25] | Differentiate ischaemic vs haemorrhagic |
| Pituitary apoplexy | Bitemporal hemianopia, headache, ophthalmoplegia | MRI pituitary with gadolinium, pituitary hormone panel [11] | Neurosurgical emergency |
High Yield Summary — Investigations in Acute Visual Loss
- The bedside examination IS the primary diagnostic tool: VA, RAPD, VF, anterior segment, fundoscopy, IOP
- RAPD (swinging flashlight test) is the most useful bedside test — localizes to optic nerve or extensive retinal disease
- Fundoscopy: cherry-red spot = CRAO; "blood and thunder" = CRVO; pale swollen disc = AAION; loss of red reflex = vitreous haemorrhage
- GCA workup: ESR + CRP urgently, CBC, temporal artery USG (halo sign), temporal artery biopsy (must be urgent, < 24-48h). Start steroids BEFORE results. ACR criteria ≥3/5 (BATHE)
- CRAO = stroke equivalent → vascular workup: carotid Doppler, ECG (AF), echocardiography, vascular risk factor bloods
- Optic neuritis: MRI brain + orbits with gadolinium (evaluate for MS lesions), anti-AQP4 (NMOSD), anti-MOG
- AACG: IOP measurement confirms (> 40-60 mmHg), slit-lamp (shallow AC, corneal oedema), gonioscopy after acute Mx
- When fundus cannot be visualized: B-scan USG (vitreous haemorrhage, retinal detachment, tumour, IOFB)
- OCT: essential for detecting macular oedema (DM macular oedema, CRVO), subretinal fluid (wet AMD, CSCR)
- Methanol poisoning: ABG + serum osmolality + anion gap + osmolal gap (> 25 = specific for toxic alcohol)
- MRI is more sensitive than CT for early ischaemic stroke (86-100% vs 48% < 1 day) and for optic nerve/posterior fossa pathology, but CT is first-line in acute stroke to exclude haemorrhage
Active Recall - Diagnostic Criteria, Algorithm, and Investigations
[1] Lecture slides: 2024 General Clerkship - Acute Visual Loss_Student Copy.pdf [2] Senior notes: Ryan Ho Neurology.pdf (Section 2 — Optic Nerve, CN II) [3] Senior notes: Maksim Medicine Notes.pdf (Section 11.8 — CNS demyelinating diseases) [5] Senior notes: Ryan Ho Opthalmology.pdf (Section 3.5.1 — Vitreous Haemorrhage) [6] Senior notes: Ryan Ho Opthalmology.pdf (Section 3.7.1 — Retinal Artery Occlusion) [8] Senior notes: Ryan Ho Opthalmology.pdf (Section 4.3.3 — Optic Neuritis) [9] Senior notes: Ryan Ho Neurology.pdf (Section 2.3 — Giant Cell Arteritis) [11] Senior notes: Block A - I keep on bumping into people on my side_ pituitary tumours; hypopituitarism.pdf [12] Senior notes: Ryan Ho Endocrine.pdf (Section 1.4.1.1 — Graves' Ophthalmopathy) [13] Senior notes: Ryan Ho Chemical Path.pdf (Section D — Methanol) [14] Senior notes: Ryan Ho Haemtology.pdf (Section 3.3.2.1 — Polycythaemia Vera) [15] Senior notes: Block A - High white cell count_ acute and chronic leukaemia; bone marrow transplantation; immunogenetics.pdf (Leukostasis) [17] Senior notes: Ryan Ho Endocrine.pdf (Section A — Diabetic Retinopathy) [18] Senior notes: Block A - Fever and a murmur_ Valvular heart diseases; Infective endocarditis.pdf [19] Senior notes: Maksim Medicine Notes.pdf (Section — GCA) [20] Senior notes: Ryan Ho Neurology.pdf (Section 2.3 — GCA diagnostic criteria) [21] Senior notes: MBBS Final MB Medicine (Felix PY Lai).pdf (Section X — Diabetic Retinopathy) [22] Senior notes: Ryan Ho Haemtology.pdf (Section — Waldenstrom's / Hyperviscosity) [23] Senior notes: Block A - High blood pressure_ hypertension.pdf (Hypertensive retinopathy) [24] Senior notes: Ryan Ho Diagnostic Radiology.pdf (Section C — CT in Stroke; Section 1 — MRI in Stroke) [25] Senior notes: Maksim Medicine Notes.pdf (Section — Acute management of stroke)
Management of Acute Visual Loss
Before diving into condition-specific management, understand three foundational principles:
- Time is vision — many causes of acute visual loss are time-critical. Irreversible damage occurs within minutes to hours for vascular causes (CRAO, GCA) and worsens with delay for others (retinal detachment, AACG, endophthalmitis).
- Treat the cause, not just the symptom — acute visual loss is always a symptom of an underlying process. The management must address both the immediate threat to vision AND the systemic underlying condition.
- Prevent fellow eye involvement — in conditions like GCA, the most important management goal is preventing the second eye from going blind.
Condition-Specific Management
1. Giant Cell Arteritis (GCA) — AAION
This is the most time-critical diagnosis because delay risks bilateral permanent blindness.
The granulomatous inflammation of the posterior ciliary arteries is an active, ongoing process. The fellow eye can become involved within days. High-dose steroids suppress the inflammatory cascade — the sooner you start, the sooner you halt the arteritis.
| Phase | Treatment | Rationale |
|---|---|---|
| Immediate (if visual symptoms present) | IV methylprednisolone 1g/day for 3 days [9][10][20] | Parenteral high-dose steroids when complications have already occurred — IV achieves faster, higher tissue concentrations than oral; suppresses granulomatous inflammation to halt optic nerve ischaemia |
| Immediate (if no visual symptoms yet) | Oral prednisolone 1-2 mg/kg/day (usually 60 mg/day) [9][20] | High-dose oral steroid sufficient if vision not yet threatened, but still urgent to prevent visual complications |
| Taper | Slowly taper over 1-2 years guided by ESR/CRP and symptoms [9] | Premature taper → relapse. GCA usually responds dramatically — complete resolution of symptoms within 48-72 hours [9]. If no response → reconsider diagnosis |
| Steroid-sparing agents | Tocilizumab (anti-IL-6) — first-line steroid-sparing agent; Methotrexate — for relapsing disease [9][10] | Tocilizumab reduces relapse rate and allows faster steroid taper. Important because prolonged high-dose steroids cause osteoporosis, DM, infections, cataracts |
| Temporal artery biopsy | Urgent, within 24-48 hours, but do NOT delay treatment [20] | Biopsy may be falsely negative (skip lesions) and steroid treatment takes weeks to alter histology — biopsy remains interpretable even days after starting steroids |
GCA — The Most Important Management Message
Start steroids IMMEDIATELY upon clinical suspicion. Do NOT wait for ESR results or biopsy results. The goal is to save the vision of the fellow eye and prevent brainstem stroke. [9][10][19][20]
The GC Rheumatology Interactive Tutorial emphasizes: "GCA is a potentially sight-threatening disease and the importance for timely diagnosis and treatment." [10]
- Osteoporosis prophylaxis: Calcium, vitamin D, ± bisphosphonate (because patients will be on steroids for 1-2 years)
- PPI: Gastroprotection during high-dose steroid therapy
- Monitor: ESR, CRP, blood glucose (steroid-induced hyperglycaemia) at each visit
2. Acute Angle-Closure Glaucoma (AACG)
The IOP in AACG is typically > 40-60 mmHg (normal 10-21). At these pressures, the retinal ganglion cells and optic nerve are being progressively damaged by ischaemia (the perfusion pressure to the optic nerve = mean arterial pressure minus IOP; when IOP is extremely high, perfusion drops dangerously). The corneal endothelium is also overwhelmed, causing oedema and pain. Every minute counts.
Phase 1: Acute IOP Lowering (Medical)
The goal is to lower IOP rapidly using multiple agents working via different mechanisms:
| Agent | Class | Mechanism | Route |
|---|---|---|---|
| Timolol 0.5% | Beta-blocker | ↓Aqueous production by blocking β-receptors on ciliary epithelium | Topical |
| Pilocarpine 2-4% | Parasympathomimetic (miotic) | Constricts pupil → opens drainage angle by pulling iris away from trabecular meshwork | Topical (given after IOP has started to fall — at very high IOP, iris sphincter is ischaemic and pilocarpine won't work) |
| Apraclonidine 1% | α2-agonist | ↓Aqueous production via α2 receptors on ciliary body | Topical |
| Acetazolamide 500mg | Carbonic anhydrase inhibitor | ↓Aqueous production by inhibiting carbonic anhydrase in ciliary epithelium (reduces HCO₃⁻ secretion into aqueous) | IV or oral |
| Mannitol 20% | Osmotic agent | Creates osmotic gradient → draws fluid out of vitreous → ↓vitreous volume → ↓IOP | IV (used if other agents fail) |
Why multiple agents? Each works by a different mechanism — combining them gives additive IOP reduction. Think of it like draining a bathtub: you can turn off the tap (↓production with timolol, apraclonidine, acetazolamide), open the drain (↑outflow with pilocarpine), and remove water from the tub (osmotic agent).
Phase 2: Definitive Treatment — Laser Peripheral Iridotomy (PI)
- Laser PI creates a small hole in the peripheral iris → allows aqueous to flow directly from posterior chamber to anterior chamber → bypasses the pupillary block → angle opens → IOP normalizes
- Performed once the acute attack has been broken and the cornea is clear enough for the laser to pass through
- Fellow eye: prophylactic laser PI — because the fellow eye has the same anatomical predisposition and is at high risk of an attack [1]
Contraindications / Cautions:
- Timolol: asthma, COPD, bradycardia, heart block (β-blocker effects are systemic even from topical drops — absorbed via nasolacrimal duct into systemic circulation)
- Pilocarpine: not effective at very high IOP (iris sphincter ischaemia); causes miosis → can worsen vision
- Acetazolamide: sulfa allergy, severe renal/hepatic impairment, hypokalaemia (it's a carbonic anhydrase inhibitor → causes metabolic acidosis and K⁺ wasting)
- Mannitol: heart failure (volume overload risk), renal failure (cannot excrete)
3. Central Retinal Artery Occlusion (CRAO)
The retina has no ischaemic tolerance — irreversible ganglion cell death begins within 90-100 minutes (similar to brain in stroke). By the time most patients present, the window for salvage has often passed. However, some interventions may help if initiated early.
| Intervention | Mechanism | Evidence / Notes |
|---|---|---|
| Ocular massage | Intermittent pressure on the globe may dislodge the embolus distally (to a branch artery, preserving more retina) | Can be done immediately at bedside. Firm digital pressure for 5-10 seconds, then release, repeated |
| Anterior chamber paracentesis | Withdrawing a small amount of aqueous humour with a needle → sudden ↓IOP → ↑perfusion pressure differential may dislodge the embolus | Performed by ophthalmologist. Acute IOP drop from ~15 to ~5 mmHg creates a "pressure wave" |
| Intra-arterial thrombolysis | Catheter-directed tPA into the ophthalmic artery to dissolve the clot | Limited evidence; considered if presenting < 4.5-6 hours. Risk of intracranial haemorrhage. Not standard of care at most centres |
| IV thrombolysis (tPA) | Systemic thrombolysis as for acute ischaemic stroke | Only if presenting within stroke thrombolysis window (< 4.5h) and no contraindications. CRAO is now classified as an acute stroke by AHA/ASA |
| Hyperbaric oxygen | ↑Dissolved O₂ in blood → delivers oxygen to retina via choroidal circulation even when retinal artery is blocked | Limited availability; some evidence of benefit if given within 8-24 hours |
| Immediate high-dose steroids | Only if GCA suspected (AAION, not pure CRAO) | Empirical — do not wait for biopsy [9] |
The most important management in CRAO is actually the systemic vascular workup — because CRAO is a stroke equivalent, the patient is at high risk of stroke. Manage like a TIA/stroke: carotid Doppler, ECG (AF), echocardiography, antiplatelet therapy (aspirin), statin, BP control, glucose control. [6]
Contraindications for thrombolysis: Same as for ischaemic stroke — previous haemorrhagic stroke, active bleeding, aortic dissection, recent intracranial surgery, severe uncontrolled HTN [26]
Treatment Protocol
| Intervention | Indication | Mechanism |
|---|---|---|
| Risk factor management | All patients | BP control (strongest risk factor), DM control, lipid control, glaucoma treatment |
| Intravitreal anti-VEGF | Macular oedema causing ↓VA | VEGF drives vascular leakage and oedema; anti-VEGF (ranibizumab, aflibercept, bevacizumab) blocks this → ↓oedema → improves vision. Given as monthly injections, then PRN |
| Intravitreal steroid | Macular oedema (alternative to anti-VEGF, especially pseudophakic patients) | Dexamethasone implant (Ozurdex) or triamcinolone — anti-inflammatory → ↓vascular permeability. Side effects: cataract, ↑IOP |
| Pan-retinal photocoagulation (PRP) | Neovascularization (ischaemic CRVO/BRVO) | Laser destroys ischaemic retina → ↓VEGF production → ↓stimulus for neovascularization. Prevents neovascular glaucoma |
| Anti-VEGF | Neovascularization (alternative/adjunct to PRP) | Directly blocks VEGF → regression of new vessels |
"90-day glaucoma": Ischaemic CRVO → extensive retinal ischaemia → massive VEGF release → neovascularization of iris (rubeosis iridis) → neovascular glaucoma, typically developing ~3 months after the occlusion. This is why close follow-up with monitoring for rubeosis is critical.
Retinal detachment is a surgical emergency — the longer the retina is detached, the more photoreceptors die, and the worse the visual outcome. If the macula is still attached ("macula-on"), urgent surgery within 24 hours is critical to preserve central vision.
Surgical Options
| Procedure | Mechanism | Indication |
|---|---|---|
| Pneumatic retinopexy | Gas bubble injected into vitreous → pushes detached retina back against RPE → retinal break sealed with cryotherapy or laser | Simple, superior RDs with single break. Least invasive |
| Scleral buckle | A silicone band is sutured onto the sclera, indenting the globe → pushes RPE toward the detached retina → closes the break from the outside | Peripheral breaks, especially in young patients. Can be combined with cryotherapy |
| Pars plana vitrectomy (PPV) | Vitreous gel is removed → vitreous traction eliminated → fluid drained from subretinal space → gas or silicone oil tamponade → retina reattached → laser/cryotherapy to seal break | Complex RDs, giant tears, PVR, posterior breaks, tractional RD. Most versatile procedure |
Tamponade agents: After vitrectomy, the vitreous cavity must be filled with a substance that holds the retina in place while healing occurs. Gas (SF₆ or C₃F₈) is absorbed over weeks (patient must maintain specific head positioning). Silicone oil is permanent and must be surgically removed later — used for complex cases.
Post-operative restrictions: Patients with gas tamponade must not fly (gas expands at altitude → ↑IOP → can cause CRAO) and must not receive nitrous oxide anaesthesia (same reason).
Management
| Severity | Management | Rationale |
|---|---|---|
| Mild/moderate, fundus partially visible | Observation — blood clears at ~1%/day [5] | The vitreous has immunological privilege → slow clearance, but it does clear spontaneously |
| Dense, non-clearing (> 1-3 months) | Pars plana vitrectomy | Removes blood and allows retinal assessment/treatment |
| Associated retinal detachment | Urgent vitrectomy | RD must be repaired to prevent permanent vision loss |
| Rubeosis iridis / NVG | Urgent vitrectomy + PRP + anti-VEGF | Rubeosis indicates ischaemia-driven neovascularization → risk of NVG if not treated |
| Underlying cause | Treat: PRP for PDR, laser for retinal tear, optimize DM control | Prevents recurrence [17][21] |
Vitreous haemorrhage is worse in the morning because blood settles on the macula overnight when supine. Patients may be advised to sleep with the head elevated. [5]
Treatment Protocol
| Intervention | Details | Rationale |
|---|---|---|
| IV methylprednisolone 1g/day for 3 days, then oral prednisolone taper over 11 days [8] | Standard ONTT (Optic Neuritis Treatment Trial) protocol | Hastens recovery but does NOT change long-term visual outcome. The natural history is spontaneous improvement over weeks |
| Oral steroids ALONE are contraindicated | The ONTT showed oral prednisone alone (without preceding IV pulse) INCREASED the recurrence rate of optic neuritis [8] | The mechanism is unclear — possibly oral-only doses are insufficient to fully suppress inflammation, leading to a rebound effect |
| Disease-modifying therapy (DMT) for MS | If MRI shows demyelinating lesions suggestive of MS → consider early DMT: glatiramer acetate, teriflunomide, interferon-β (Betaferon/Rebif) [8] | Early DMT reduces the rate of conversion to clinically definite MS and reduces future relapse frequency |
| Anti-AQP4 positive (NMOSD) | Different treatment from MS: rituximab (anti-CD20), eculizumab (anti-C5), satralizumab (anti-IL6R) | NMOSD requires distinct immunotherapy. MS DMTs (e.g., interferon-β, fingolimod) can worsen NMOSD |
| Observation | If mild visual loss, non-disabling | Spontaneous recovery occurs in most patients |
Optic Neuritis — Key Treatment Pitfall
Oral steroids ALONE are contraindicated in optic neuritis — they increase the recurrence rate. Always give IV methylprednisolone first if you decide to treat. However, treatment only hastens recovery; long-term visual outcome is the same. [8]
Treatment
| Agent | Class | Mechanism | Administration |
|---|---|---|---|
| Ranibizumab (Lucentis) | Anti-VEGF monoclonal antibody fragment | Binds VEGF-A → inhibits vascular leakage and neovascularization | Intravitreal injection, monthly or treat-and-extend protocol |
| Aflibercept (Eylea) | VEGF-trap (fusion protein) | Binds VEGF-A, VEGF-B, and PlGF → broader VEGF blockade | Intravitreal injection, Q8 weekly after loading |
| Bevacizumab (Avastin) | Full anti-VEGF monoclonal antibody | Same as ranibizumab but full antibody (off-label but widely used due to lower cost) | Intravitreal injection |
| Faricimab (Vabysmo) | Bispecific antibody: anti-VEGF-A + anti-Ang2 | Dual mechanism: blocks VEGF and destabilizing angiopoietin-2 → ↓vascular instability | Intravitreal injection, longer intervals possible |
Why intravitreal? The blood-retinal barrier prevents systemic drugs from reaching therapeutic concentrations in the eye. Direct intravitreal injection bypasses this barrier.
The GC PBL Patient 3 with central scotoma and metamorphopsia (classic wet AMD) would be treated with intravitreal anti-VEGF. [1]
This is a common exam topic because DM is so prevalent in Hong Kong.
| Stage | Treatment | Mechanism / Rationale |
|---|---|---|
| Mild-Moderate NPDR | Glycaemic control (HbA1c ≤ 7%), BP control (≤ 140/90), lipid control [17][21][27] | Risk factor modification slows progression. No laser needed unless macular oedema |
| Severe NPDR | Pan-retinal photocoagulation (PRP) | 52-75% progress to PDR → prophylactic PRP reduces this risk [17] |
| Proliferative DR | PRP + intravitreal anti-VEGF (ranibizumab/aflibercept/bevacizumab) ± cryotherapy [17] | PRP destroys ischaemic retina → ↓VEGF → regression of new vessels. Anti-VEGF directly blocks neovascularization |
| Diabetic macular oedema | Intravitreal anti-VEGF (first-line) ± intravitreal steroid (triamcinolone/Ozurdex) ± focal/grid laser [17] | Anti-VEGF blocks vascular leakage at macula. Steroid has anti-inflammatory and anti-permeability effects |
| Vitreous haemorrhage / Tractional RD | Vitrectomy [17][27] | Removes blood, relieves traction, allows retinal reattachment |
| Neovascular glaucoma (rubeotic) | Anti-VEGF + PRP + glaucoma treatment (topical/surgical) | Must address the ischaemic drive (PRP + anti-VEGF) AND the elevated IOP |
Complications of PRP to be aware of: Pain during treatment, loss of dark adaptation (poor night vision), visual field loss, visual acuity loss. [27] These are trade-offs — you sacrifice some peripheral retina to save central vision.
| Intervention | Indication | Details |
|---|---|---|
| Emergency transsphenoidal surgery | Visual loss, ophthalmoplegia, altered consciousness [11] | Decompresses optic chiasm and removes haemorrhagic/necrotic pituitary tissue |
| Hormone replacement | Acute adrenal crisis prevention | IV hydrocortisone 100mg stat then 50mg Q8h (the pituitary may no longer produce ACTH → adrenal insufficiency → Addisonian crisis can be fatal). Also assess and replace thyroid, gonadal hormones |
| Conservative management | Stable visual fields, no ophthalmoplegia, stable consciousness | Close monitoring with serial visual fields. Surgery if deterioration |
Managed as per standard acute stroke protocol: [25]
| Timeframe | Intervention | Details |
|---|---|---|
| Immediate | NCCT brain | Exclude haemorrhage [24] |
| *** < 4.5 hours*** | IV tPA (alteplase/tenecteplase) | If no contraindications. Aim door-to-needle time ≤ 60 min |
| *** < 24 hours with LVO*** | Endovascular thrombectomy | If large vessel occlusion confirmed on CTA/MRA (basilar artery, PCA) |
| Post-acute | Antiplatelet (aspirin ± clopidogrel), statin, BP control, AF management if indicated | Secondary prevention [25] |
| Intervention | Mechanism | Details |
|---|---|---|
| Fomepizole (first-line) or ethanol | Competitive inhibitor of alcohol dehydrogenase → blocks conversion of methanol to formaldehyde → prevents formic acid accumulation | Fomepizole preferred (fewer side effects than ethanol). Ethanol is the alternative if fomepizole unavailable |
| Haemodialysis | Removes methanol and formic acid directly from the blood | Indicated if: significant metabolic acidosis, visual symptoms, renal failure, methanol level > 50 mg/dL |
| Folic acid / folinic acid (leucovorin) | Folic acid is a cofactor for the enzyme that converts formic acid → CO₂ + H₂O → enhances formate metabolism | Given to all suspected cases |
| Supportive | Correct metabolic acidosis (IV NaHCO₃), monitor ABG, electrolytes | [13] |
| Condition | Urgency | Key Treatment | Must Not Forget |
|---|---|---|---|
| GCA/AAION | Minutes | IV methylprednisolone → oral pred taper → tocilizumab | Start BEFORE biopsy. Protect fellow eye |
| AACG | Minutes-hours | Topical/systemic IOP-lowering agents → laser PI | Fellow eye prophylactic PI |
| CRAO | Minutes-hours | Ocular massage, AC paracentesis, ?thrombolysis | Vascular workup (stroke equivalent) |
| RD (macula-on) | Hours | Urgent vitrectomy/scleral buckle | "Macula-on" = urgent within 24h |
| Endophthalmitis | Hours | Intravitreal antibiotics ± vitrectomy | Post-op eye with pain + ↓vision = endophthalmitis until proven otherwise |
| CRVO | Days | Anti-VEGF for macular oedema, PRP if neovascularization | Monitor for "90-day glaucoma" |
| Optic neuritis | Days | IV methylprednisolone (if treating). MRI for MS | Oral steroids alone are contraindicated |
| Wet AMD | Days-weeks | Intravitreal anti-VEGF | Treat-and-extend protocol |
| VH | Weeks (if no RD) | Observation → vitrectomy if non-clearing | USG to rule out associated RD |
| Occipital stroke | Minutes | Acute stroke pathway: NCCT → tPA ± thrombectomy | Standard stroke management |
| Methanol | Hours | Fomepizole/ethanol + haemodialysis + folic acid | ABG, osmolal gap, anion gap |
High Yield Summary — Management of Acute Visual Loss
- GCA: Start high-dose steroids IMMEDIATELY upon clinical suspicion. IV methylprednisolone if visual symptoms present. Do NOT wait for biopsy. Taper slowly over 1-2 years. Tocilizumab as steroid-sparing agent. Dramatic response within 48-72 hours expected
- AACG: Multiple agents to lower IOP (timolol + apraclonidine + acetazolamide ± pilocarpine ± mannitol). Definitive: laser peripheral iridotomy (PI). Fellow eye prophylactic PI
- CRAO: Ocular massage, AC paracentesis, consider thrombolysis if early. Most importantly: vascular workup like a stroke (carotid Doppler, ECG, echo, antiplatelet, statin)
- Retinal detachment: Surgical emergency. PPV, scleral buckle, or pneumatic retinopexy. "Macula-on" = urgent within 24 hours
- Optic neuritis: IV methylprednisolone 1g/day x 3 days → oral taper. Oral steroids ALONE are contraindicated (↑recurrence). Hastens recovery but does NOT change long-term visual outcome. MRI for MS workup
- Wet AMD: Intravitreal anti-VEGF (ranibizumab, aflibercept, bevacizumab). Monthly or treat-and-extend
- Diabetic retinopathy: Risk factor control for early stages. PRP for severe NPDR and PDR. Anti-VEGF for macular oedema and neovascularization. Vitrectomy for VH and tractional RD
- Vitreous haemorrhage: Observation if mild (blood clears ~1%/day). Vitrectomy if non-clearing, associated RD, or rubeosis
- PRP complications: pain, poor night vision, VF loss, VA loss — these are acceptable trade-offs to save central vision
- Methanol: Fomepizole (or ethanol) + haemodialysis + folic acid. Block alcohol dehydrogenase, remove toxin, enhance formate metabolism
Active Recall - Management of Acute Visual Loss
[1] Lecture slides: 2024 General Clerkship - Acute Visual Loss_Student Copy.pdf [5] Senior notes: Ryan Ho Opthalmology.pdf (Section 3.5.1 — Vitreous Haemorrhage) [6] Senior notes: Ryan Ho Opthalmology.pdf (Section 3.7.1 — Retinal Artery Occlusion) [8] Senior notes: Ryan Ho Opthalmology.pdf (Section 4.3.3 — Optic Neuritis) [9] Senior notes: Ryan Ho Rheumatology.pdf (Section 3.6.1 — Giant Cell Arteritis) [10] Senior notes: Block A - Rheumatology Interactive Tutorial.pdf (Case 1 — GCA/PMR) [11] Senior notes: Block A - I keep on bumping into people on my side_ pituitary tumours; hypopituitarism.pdf [13] Senior notes: Ryan Ho Chemical Path.pdf (Section D — Methanol) [17] Senior notes: Ryan Ho Endocrine.pdf (Section A — Diabetic Retinopathy) [19] Senior notes: Maksim Medicine Notes.pdf (Section — GCA) [20] Senior notes: Ryan Ho Neurology.pdf (Section 2.3 — GCA diagnostic criteria) [21] Senior notes: MBBS Final MB Medicine (Felix PY Lai).pdf (Section X — Diabetic Retinopathy) [24] Senior notes: Ryan Ho Diagnostic Radiology.pdf (Section C — CT in Stroke) [25] Senior notes: Maksim Medicine Notes.pdf (Section — Acute management of stroke) [26] Senior notes: Ryan Ho Cardiology.pdf (Contraindications to thrombolysis) [27] Senior notes: MBBS Final MB Medicine (Felix PY Lai).pdf (Section 6 — Treatment of DR)
Complications of Acute Visual Loss (and Its Underlying Causes)
Complications in acute visual loss arise from two sources: (1) complications of the underlying condition if not treated or if treated inadequately, and (2) complications of the treatments themselves. Both are commonly examined. The key message running through this section is that many causes of acute visual loss are "gateway diagnoses" — they point to systemic diseases with their own serious complications beyond the eye.
1. Complications of Specific Causes of Acute Visual Loss
1A. Central Retinal Artery Occlusion (CRAO)
| Complication | Mechanism | Timeline |
|---|---|---|
| Permanent severe visual loss | Retinal ganglion cells have no ischaemic tolerance — irreversible death within 90–100 minutes. By the time most patients present, the damage is done | Immediate |
| Neovascularization (retinal, iris, angle) | If enough retina survives under chronically hypoxic conditions → VEGF release → new fragile vessels grow on the retina, iris (rubeosis iridis), and drainage angle | Usually apparent after 2-3 months [6] |
| Neovascular (rubeotic) glaucoma | Neovascularization of the iris and angle → fibrovascular membrane covers the trabecular meshwork → secondary angle closure → ↑IOP → optic nerve damage. Up to 18% risk after CRAO [6] | 2–3 months post-occlusion |
| Vitreous haemorrhage | Fragile neovascular vessels rupture → blood fills the vitreous. Occurs in < 2% of CRAO [6] | Weeks to months |
This is the most important "complication" to understand: a patient with CRAO carries the same vascular risk as a stroke patient. [1][6]
| Complication | Mechanism | Why It Matters |
|---|---|---|
| Subsequent cerebrovascular accident (stroke) | The same embolic sources (carotid atherosclerosis, AF, valvular disease) that caused CRAO can send emboli to the brain | CRAO patients have a significantly elevated short-term risk of stroke — this is why vascular workup is mandatory |
| Myocardial infarction | Shared atherosclerotic risk factors; coronary artery disease often coexists | Screen and manage cardiovascular risk factors |
| Peripheral vascular disease | Systemic atherosclerosis | Part of the comprehensive vascular workup |
| Complication | Mechanism | Timeline |
|---|---|---|
| Macular oedema (most common cause of ↓VA in RVO) | Venous congestion → ↑hydrostatic pressure → breakdown of blood-retinal barrier → fluid accumulates at the macula | Acute to weeks |
| "90-day glaucoma" (neovascular glaucoma) | Ischaemic CRVO → extensive retinal ischaemia → massive VEGF release → rubeosis iridis → neovascularization of angle → fibrovascular membrane occludes trabecular meshwork → ↑IOP. Why "90-day"? Neovascularization typically develops ~3 months after the initial occlusion | ~3 months post-CRVO |
| Vitreous haemorrhage | Neovascularization produces fragile vessels → rupture into vitreous | Weeks to months |
| Retinal detachment (tractional) | Fibrovascular proliferation associated with neovascularization → traction on retina → detachment | Months |
| Chronic macular ischaemia | Persistent capillary non-perfusion near the macula → irreversible photoreceptor damage → permanently reduced VA | Ongoing if ischaemic type |
Ischaemic vs Non-Ischaemic RVO — Different Complication Profiles
Non-ischaemic CRVO: Fewer haemorrhages, better VA at presentation, lower risk of neovascularization. May convert to ischaemic type over months → requires monitoring.
Ischaemic CRVO: Extensive haemorrhages, cotton wool spots, poor VA at presentation, high risk of neovascularization and neovascular glaucoma. Close follow-up essential to detect rubeosis early. [6]
1C. Giant Cell Arteritis (GCA)
GCA has both ocular and systemic complications, making it one of the most dangerous causes of acute visual loss.
| Complication | Mechanism | Key Points |
|---|---|---|
| Permanent bilateral blindness | AAION (arteritic anterior ischaemic optic neuropathy): granulomatous arteritis of posterior ciliary arteries → optic nerve infarction. Risk of fellow eye involvement is up to 50% if untreated [9][10] | This is THE feared complication — the reason treatment must not be delayed |
| Central retinal artery occlusion | GCA can cause thrombotic occlusion of the CRA itself (not just the posterior ciliary arteries) | Less common than AAION but possible |
| Posterior ischaemic optic neuropathy (PION) | Ischaemia of the retrobulbar optic nerve — disc appears normal initially but vision is lost | Less common; may be bilateral |
| Complication | Mechanism | Key Points |
|---|---|---|
| Aortic aneurysm and dissection | GCA is a large-vessel vasculitis — granulomatous inflammation of the aortic wall → weakening → aneurysm formation → risk of dissection | Long-term complication — requires surveillance imaging. Thoracic aortic aneurysm risk is 17× higher in GCA patients [9] |
| Large artery stenosis / occlusion | Granulomatous inflammation → intimal hyperplasia → luminal narrowing of aortic branches (subclavian, axillary, carotid) | May present as limb claudication, discrepant BP between arms, absent pulses |
| Posterior circulation stroke | Vertebrobasilar artery involvement → brainstem ischaemia | High-dose steroids prevent brainstem stroke as well as blindness [19] |
| Treatment Complication | Mechanism | Prevention |
|---|---|---|
| Steroid-induced osteoporosis | Chronic corticosteroid use → ↓osteoblast activity, ↑osteoclast activity → bone loss | Calcium, vitamin D, bisphosphonate prophylaxis |
| Steroid-induced diabetes | Corticosteroids → hepatic gluconeogenesis ↑, peripheral insulin resistance ↑ | Monitor blood glucose; adjust DM medications if pre-existing DM |
| Steroid-induced infections | Immunosuppression → increased susceptibility to opportunistic infections (TB reactivation, pneumocystis) | Screen for latent TB before starting prolonged steroids |
| Steroid-induced cataracts | Posterior subcapsular cataract from altered lens protein metabolism | Monitor; ophthalmology follow-up |
| Steroid-induced glaucoma | ↑IOP from ↑aqueous production and ↓outflow facility | Monitor IOP |
| GI complications | Peptic ulcer disease, GI bleeding | PPI co-prescription |
| Adrenal suppression on taper | Chronic exogenous steroids suppress the HPA axis → if tapered too quickly, risk of adrenal crisis | Gradual taper over 1–2 years |
| Complication | Mechanism | Key Points |
|---|---|---|
| Permanent visual loss (if macula detached) | Once the macula detaches from the RPE, the photoreceptors lose their metabolic support → progressive cell death. Irreversible ↓vision if macula detached for > 24 hours preoperatively, though surgery still confers substantial recovery [28] | This is why "macula-on" RD is a surgical emergency within 24 hours |
| Proliferative vitreoretinopathy (PVR) | Fibrotic changes in vitreous and on retinal surface after repair failure (occurs in 8-10% of cases) → further traction on retina → tractional retinal detachment [28] | The most common cause of failed retinal detachment surgery. May require repeat, more complex surgery |
| Recurrent detachment | Inadequate seal of retinal break, new breaks, PVR | Requires re-operation |
| Phthisis bulbi (end-stage) | Chronic, untreated detachment → complete retinal atrophy → globe shrinks and becomes non-functional | Irreversible; disfiguring. Rarely seen in modern practice due to surgical intervention |
| Cataract (iatrogenic) | Gas or silicone oil tamponade → altered lens metabolism → cataract formation. Also, vitrectomy itself accelerates cataract formation | Very common post-vitrectomy complication — most patients need cataract surgery within 1-2 years |
| Complication | Mechanism | Key Points |
|---|---|---|
| Permanent optic nerve damage (glaucomatous optic neuropathy) | Sustained very high IOP → ischaemic damage to retinal ganglion cell axons at the optic disc → progressive optic atrophy → irreversible visual field loss | The longer the attack persists, the worse the damage. This is why rapid IOP lowering is critical |
| Iris atrophy and synechiae | Ischaemia of the iris from ↑IOP → iris sphincter necrosis → sector iris atrophy. Inflammatory adhesions form between iris and lens (posterior synechiae) or iris and cornea (peripheral anterior synechiae, PAS) | PAS can permanently close the drainage angle, converting to chronic angle-closure glaucoma |
| Chronic angle-closure glaucoma | Post-attack PAS progressively close the angle → chronic ↑IOP → ongoing optic nerve damage | Requires long-term IOP monitoring and potentially filtration surgery (trabeculectomy) |
| Cataract (glaukomflecken) | Acute ↑IOP → focal lens epithelial necrosis → small, white, anterior subcapsular opacities called "glaukomflecken" — pathognomonic sign of previous acute attack | These are irreversible but usually don't significantly affect vision |
| Corneal decompensation | Severe acute ↑IOP → irreversible corneal endothelial cell loss → chronic corneal oedema | Rare with prompt treatment |
| Fellow eye attack | The fellow eye has the same anatomical predisposition (shallow AC, hypermetropia) → risk of acute attack in the fellow eye if prophylactic laser PI is not performed | Prophylactic laser PI in the fellow eye is mandatory |
The AOS Ophthalmology PBL (Scenario 2) asks about treatment options including gonioscopy-guided management — the complications of untreated or recurrent angle closure include chronic glaucomatous optic neuropathy requiring filtration surgery. [29]
| Complication | Mechanism | Key Points |
|---|---|---|
| Failure to detect underlying retinal detachment | Dense vitreous haemorrhage obscures the fundus → retinal tear or detachment may be missed | Always perform B-scan USG when fundus cannot be visualized [5] |
| Recurrent haemorrhage | If the underlying cause (e.g., PDR) is not treated, neovascularization persists → recurrent bleeds | Treat underlying cause: PRP for PDR |
| Ghost cell glaucoma | Old degenerated RBCs ("ghost cells") become rigid and block the trabecular meshwork → ↑IOP | Rare; occurs with long-standing vitreous haemorrhage |
| Haemosiderosis bulbi | Chronic vitreous blood → iron from haemoglobin becomes toxic to retinal tissue → progressive retinal degeneration | Another reason to perform vitrectomy for non-clearing VH |
| Complication | Mechanism | Key Points |
|---|---|---|
| Incomplete visual recovery | Demyelination may result in permanent axonal loss, especially if severe or recurrent. Worse prognosis if ↓VA at presentation or longer lesion in optic nerve [8] | Most patients recover good vision, but some have residual ↓contrast sensitivity or colour vision deficits |
| Recurrence | 35% recurrence rate at 10 years, ↑↑ if MS or NMOSD [8] | Recurrent episodes cause cumulative damage |
| Progression to Multiple Sclerosis | 30% at 5 years, 50% at 15 years (median duration 3 years). RFs for progression: early adulthood onset, female, MRI lesions, recurrent ON, lack of papillitis, oligoclonal bands on LP [8] | This is why MRI brain is done at the time of first ON — to assess MS risk |
| Optic atrophy | Repeated attacks of ON → cumulative loss of retinal ganglion cell axons → the disc becomes pale (especially temporal pallor on fundoscopy) | Irreversible once established |
| NMOSD-related complications | If the ON is due to NMOSD rather than MS, it tends to be more severe, bilateral, and recurrent with poorer visual recovery [3]. NMOSD is also associated with longitudinally extensive transverse myelitis | Different treatment from MS — MS DMTs can worsen NMOSD |
Diabetic retinopathy is typically a chronic condition, but its complications present as acute visual loss. Understanding this connection is high-yield.
The GC PBL Patient 1 asks: "What are the major ocular complications of this condition?" [1] — referring to the ocular complications of DM causing acute visual loss.
The 5 important ocular complications of diabetes mellitus: [17][30]
| Complication | Mechanism | Presentation |
|---|---|---|
| Diabetic retinopathy (NPDR → PDR) | Chronic hyperglycaemia → retinal microangiopathy → ischaemia → neovascularization | Gradual progression; sudden visual loss from its complications |
| Diabetic macular oedema | Breakdown of blood-retinal barrier → fluid leakage at the macula. Commonest cause of vision loss in DM patients. Can occur at any stage of DR [17] | Gradual central blurring |
| Vitreous haemorrhage | Neovascularization (PDR) → fragile vessels rupture into vitreous [30] | Sudden painless visual loss |
| Tractional retinal detachment | Fibrous proliferation / scar formation after bleeding → fibrovascular membranes contract → traction on retina → detachment [30] | Progressive visual field loss or sudden central visual loss if macula involved |
| Neovascular glaucoma | VEGF from ischaemic retina "has nowhere to go" when the whole retina is ischaemic → moves anteriorly to the iris → rubeosis iridis → fibrosis → acute angle closure [17][30] | Painful red eye with very high IOP |
| Cataract | Activation of pentose (polyol/sorbitol) pathway → accumulation of sorbitol within the lens → osmotic swelling → lens opacification [17][30] | Gradual blurring (chronic, not acute) |
| CN III, IV, VI palsies | Diabetic mononeuropathy (mononeuritis multiplex): ischaemic infarction of the vasa nervorum supplying the cranial nerves [17][30] | Ptosis and divergent squint (CN III — typically pupil-sparing), lateral rectus palsy (CN VI) |
Why is Diabetic CN III Palsy Typically Pupil-Sparing?
In diabetic mononeuropathy, the ischaemic damage preferentially affects the core of the nerve (where the motor fibres to the extraocular muscles run). The pupillary parasympathetic fibres travel on the periphery (surface) of CN III and receive their blood supply from the pial vasculature — they are spared in microvascular (diabetic) CN III palsy. In contrast, a compressive lesion (e.g., posterior communicating artery aneurysm) compresses the nerve from outside in → the superficial pupillary fibres are affected FIRST → "pupil-involving" CN III palsy = red flag for aneurysm. [17]
Sight-threatening complications include: [12]
| Complication | Mechanism | Key Points |
|---|---|---|
| Compressive optic neuropathy ( < 5%) | Oversized recti + orbital fat → apical crowding → compressive optic neuropathy. Symptoms: slowly progressive ↓vision (especially colour vision, contrast sensitivity). Signs: optic disc oedema/pallor, RAPD+, central scotoma with inferior arcuate defects [12] | Requires urgent IV methylprednisolone ± orbital decompression surgery |
| Exposure keratopathy | RFs: lagophthalmos (incomplete eyelid closure), degree of proptosis, integrity of Bell's reflex. Sequence: chemosis → punctate erosions → corneal ulcer → corneal perforation [12] | Managed with lubricants, taping eyelids at night; severe cases need surgical correction |
| Secondary open-angle glaucoma | ↑Episcleral venous pressure + EOM swelling compressing the globe → ↑IOP [12] | Monitor IOP in all Graves' patients with orbitopathy |
2. Complications of Treatments for Acute Visual Loss
| Complication | Mechanism |
|---|---|
| Pain during treatment | Laser energy absorbed by RPE → thermal damage → pain (ciliary nerve stimulation) |
| Loss of dark adaptation (poor night vision) | Laser destroys rod photoreceptors in the peripheral retina (rods predominate in the periphery and are responsible for scotopic vision) |
| Visual field (VF) loss | Destruction of peripheral retina → loss of corresponding peripheral visual field |
| Visual acuity (VA) loss | Scattered laser burns, macular oedema from treatment |
These complications are trade-offs — you sacrifice peripheral vision to save central vision by reducing VEGF-driven neovascularization. [27]
| Complication | Mechanism |
|---|---|
| Endophthalmitis | Infection introduced during injection (rare, ~1/2000–1/5000 per injection). Minimized by sterile technique and povidone-iodine prep |
| Retinal detachment | Rare complication of the injection itself |
| Raised IOP (transient) | Volume of injected fluid temporarily ↑IOP |
| Vitreous haemorrhage | Needle may traumatize intraocular vessels |
| Systemic thromboembolic events | Anti-VEGF has potential systemic absorption → theoretical ↑risk of MI, stroke. Clinically very low but considered in high-risk patients |
| Complication | Mechanism |
|---|---|
| Cataract | Steroid-induced posterior subcapsular cataract (well-established dose-dependent complication) |
| Raised IOP / Steroid-induced glaucoma | Steroids alter trabecular meshwork extracellular matrix → ↓aqueous outflow → ↑IOP |
| Endophthalmitis | Same injection-related risk as anti-VEGF |
| Complication | Mechanism |
|---|---|
| Cataract (very common) | Vitrectomy alters the lens environment (↑oxygen exposure to the posterior lens) → accelerated nuclear sclerotic cataract. Most phakic patients develop cataract within 1-2 years |
| Retinal detachment | Iatrogenic retinal breaks during surgery |
| Endophthalmitis | Post-surgical intraocular infection |
| Recurrent vitreous haemorrhage | Persistent neovascularization (if underlying cause not adequately treated) |
| Raised IOP | From gas/silicone oil tamponade, inflammation, or ghost cell glaucoma |
| Complication | Mechanism |
|---|---|
| ↑IOP → CRAO if flying | Gas expands at altitude (Boyle's law: ↓pressure → ↑volume) → IOP rises dangerously → can cause CRAO [28] |
| ↑IOP with nitrous oxide anaesthesia | Nitrous oxide diffuses into the gas bubble faster than inert gases (SF₆, C₃F₈) diffuse out → bubble expands → ↑IOP |
Patients with intraocular gas MUST NOT fly and MUST NOT receive nitrous oxide anaesthesia until the gas has fully absorbed (2-8 weeks depending on the gas used). [28]
As covered in the GCA section above — osteoporosis, diabetes, infections, cataracts, glaucoma, adrenal suppression, GI complications.
| Drug | Ocular Complication | Mechanism |
|---|---|---|
| Ethambutol | Optic neuritis (blurring of vision, scotoma, ↓colour discrimination) [31] | Direct toxic effect on retinal ganglion cells. Risk increases with renal impairment (drug accumulates) |
| Hydroxychloroquine | Bull's eye maculopathy [32] | Accumulates in RPE → toxicity to photoreceptors in a ring around the fovea. Screening: eye check before treatment and annually after 5 years of use [32] |
| Corticosteroids (topical or systemic) | Cataract, ↑IOP | As above |
| Amiodarone | Corneal microdeposits (vortex keratopathy), optic neuropathy (rare) | Drug deposits in corneal epithelium |
| Tamoxifen | Crystalline maculopathy, macular oedema | Toxic to retinal cells at high doses |
| Condition | Immediate Ocular Complications | Delayed Ocular Complications | Systemic Complications |
|---|---|---|---|
| CRAO | Permanent severe visual loss | Neovascularization, NVG (2-3 months), VH | Stroke, MI (stroke equivalent) |
| CRVO | Macular oedema, ↓VA | "90-day glaucoma" (NVG), VH, tractional RD | HTN, DM complications |
| GCA | AAION → permanent blindness, fellow eye risk | Optic atrophy | Aortic aneurysm/dissection, stroke |
| Retinal detachment | Progressive visual field/central loss | PVR, recurrent detachment | None specific |
| AACG | Optic nerve damage, corneal oedema | Chronic angle-closure glaucoma, PAS, iris atrophy | None specific |
| Vitreous haemorrhage | Variable visual loss | Ghost cell glaucoma, haemosiderosis | Underlying DM complications |
| Optic neuritis | Acute visual loss | Optic atrophy, recurrence | MS (30% at 5y, 50% at 15y), NMOSD |
| Diabetic retinopathy | VH, NVG, tractional RD, macular oedema | Progressive retinopathy | Nephropathy, neuropathy, cardiovascular disease |
| Graves' orbitopathy | Exposure keratopathy | Compressive optic neuropathy, secondary glaucoma | Thyroid storm, cardiac complications |
High Yield Summary — Complications of Acute Visual Loss
- CRAO complications: neovascularization (2-3 months), neovascular glaucoma (up to 18%), vitreous haemorrhage. CRAO is a stroke equivalent — subsequent stroke and MI are the most important systemic complications
- CRVO: "90-day glaucoma" — neovascular glaucoma from ischaemic CRVO developing ~3 months post-occlusion via VEGF-driven rubeosis iridis
- GCA: bilateral permanent blindness (fellow eye at 50% risk if untreated), aortic aneurysm/dissection (17× risk), posterior circulation stroke. Steroid side effects are a major management consideration
- Retinal detachment: irreversible vision loss if macula detached > 24 hours. PVR (8-10%) is the most common cause of failed RD surgery
- AACG: permanent glaucomatous optic neuropathy, chronic angle closure from PAS, fellow eye attack if prophylactic PI not performed
- Optic neuritis: progression to MS (50% at 15 years), recurrence (35% at 10 years), optic atrophy
- Diabetic retinopathy complications causing acute visual loss: vitreous haemorrhage, tractional RD, neovascular glaucoma, diabetic macular oedema
- Treatment complications: PRP causes night vision loss and VF loss (trade-off); anti-VEGF risks endophthalmitis; vitrectomy accelerates cataract; gas tamponade contraindicated with flying and nitrous oxide
- Drug-induced: ethambutol → optic neuritis (worse with renal impairment); hydroxychloroquine → bull's eye maculopathy (screen annually after 5 years)
- Diabetic CN III palsy is pupil-sparing because ischaemia affects the core motor fibres (central in the nerve), while the pupillary parasympathetic fibres run on the surface and receive separate blood supply
Active Recall - Complications of Acute Visual Loss
References
[1] Lecture slides: 2024 General Clerkship - Acute Visual Loss_Student Copy.pdf [3] Senior notes: Maksim Medicine Notes.pdf (Section 11.8 — CNS demyelinating diseases) [5] Senior notes: Ryan Ho Opthalmology.pdf (Section 3.5.1 — Vitreous Haemorrhage) [6] Senior notes: Ryan Ho Opthalmology.pdf (Section 3.7.1 — Retinal Artery Occlusion, Complications) [8] Senior notes: Ryan Ho Opthalmology.pdf (Section 4.3.3 — Optic Neuritis) [9] Senior notes: Ryan Ho Rheumatology.pdf (Section 3.6.1 — Giant Cell Arteritis) [10] Senior notes: Block A - Rheumatology Interactive Tutorial.pdf (Case 1 — GCA/PMR) [12] Senior notes: Ryan Ho Endocrine.pdf (Section 1.4.1.1 — Graves' Ophthalmopathy) [17] Senior notes: Ryan Ho Endocrine.pdf (Section A — Diabetic Retinopathy) [19] Senior notes: Maksim Medicine Notes.pdf (Section — GCA) [27] Senior notes: MBBS Final MB Medicine (Felix PY Lai).pdf (Section 6 — Treatment of DR) [28] Senior notes: Ryan Ho Opthalmology.pdf (Section 3.5 — Retinal Detachment, Management and Prognosis) [29] AOS material: AOS - Ophthalmology.pdf (Scenario 2 — AACG) [30] Senior notes: Block A - Deterioration of eyesight in a diabetic patient_ diabetic complications.pdf [31] Senior notes: Gen Clerk Anaes + Microbiology Summary.pdf (Ethambutol — ocular complications) [32] Senior notes: Ryan Ho Rheumatology.pdf (Section — SLE Management, HCQ)
High Yield Summary
Acute Visual Loss — Key Points for Exams:
- Acute visual loss is a symptom, not a diagnosis — systematic anatomical localization is the approach
- Key history questions: laterality, pain, transient vs persistent, flashes/floaters, GCA symptoms, neurological symptoms
- Key examinations: VA (Snellen chart, pinhole correction), RAPD (swinging flashlight test — most useful bedside test), confrontation visual fields, anterior segment (red eye, corneal clarity, pupil shape/reactivity, anterior chamber depth), fundoscopy, IOP
- RAPD = optic nerve or extensive retinal lesion on the affected side. Absent in media opacity, macular disease, refractive error, retrochiasmal lesions
- CRAO = stroke equivalent — needs urgent vascular workup. Fundus: cherry-red spot + pale retina + attenuated arteries. RAPD always present
- GCA (AAION) = ophthalmic emergency in elderly ( > 50y). Must check ESR/CRP. Start high-dose steroids BEFORE biopsy. Jaw claudication is most specific symptom. Risk of fellow eye involvement if untreated
- Optic neuritis: young patient, painful (worse on eye movement), subacute, ↓colour vision, RAPD+. Associated with MS, NMOSD, MOG-IgG disease
- AACG: painful red eye, halos, N/V, mid-dilated fixed pupil, shallow anterior chamber, very high IOP. More common in East Asians
- New floaters + flashes = PVD ± retinal tear → urgent dilated fundoscopy to rule out retinal tear/detachment
- Vitreous haemorrhage: sudden painless visual loss, worse in morning, loss of red reflex. Most common cause = proliferative DR
High Yield Summary — Differential Diagnosis of Acute Visual Loss
- Organize the differential anatomically: ocular media → retina → optic nerve → chiasm/retrochiasmal → transient → systemic
- Three key axes for differentiation: laterality (unilateral vs bilateral), pain (painful vs painless), duration (transient vs persistent)
- RAPD localizes to optic nerve or extensive retinal disease — absent in media opacity, macular disease, refractive error, retrochiasmal lesions
- Fundoscopy is the single most discriminating examination: cherry-red spot = CRAO, "blood and thunder" = CRVO, pale swollen disc = AAION, elevated retina = RD, loss of red reflex = vitreous haemorrhage
- CRAO = stroke equivalent — always investigate for carotid disease, cardiac source, vascular risk factors
- GCA must be excluded in ANY patient > 50y with acute visual loss — ask about temporal headache, jaw claudication, scalp tenderness, PMR symptoms, check ESR/CRP urgently
- Optic neuritis: young, painful (eye movement), subacute, ↓colour vision, RAPD+, associated with MS/NMOSD/MOG
- AACG: more common in East Asians (Hong Kong relevance), painful red eye, halos, N/V, mid-dilated fixed pupil, ↑↑IOP
- New floaters + flashes with good VA does NOT provide reassurance — must urgently exclude retinal tear/detachment
- Methanol: bilateral visual loss + "snowstorm" vision + metabolic acidosis (↑AG, ↑OG) — formic acid inhibits cytochrome c oxidase → optic nerve toxicity
High Yield Summary — Investigations in Acute Visual Loss
- The bedside examination IS the primary diagnostic tool: VA, RAPD, VF, anterior segment, fundoscopy, IOP
- RAPD (swinging flashlight test) is the most useful bedside test — localizes to optic nerve or extensive retinal disease
- Fundoscopy: cherry-red spot = CRAO; "blood and thunder" = CRVO; pale swollen disc = AAION; loss of red reflex = vitreous haemorrhage
- GCA workup: ESR + CRP urgently, CBC, temporal artery USG (halo sign), temporal artery biopsy (must be urgent, < 24-48h). Start steroids BEFORE results. ACR criteria ≥3/5 (BATHE)
- CRAO = stroke equivalent → vascular workup: carotid Doppler, ECG (AF), echocardiography, vascular risk factor bloods
- Optic neuritis: MRI brain + orbits with gadolinium (evaluate for MS lesions), anti-AQP4 (NMOSD), anti-MOG
- AACG: IOP measurement confirms (> 40-60 mmHg), slit-lamp (shallow AC, corneal oedema), gonioscopy after acute Mx
- When fundus cannot be visualized: B-scan USG (vitreous haemorrhage, retinal detachment, tumour, IOFB)
- OCT: essential for detecting macular oedema (DM macular oedema, CRVO), subretinal fluid (wet AMD, CSCR)
- Methanol poisoning: ABG + serum osmolality + anion gap + osmolal gap (> 25 = specific for toxic alcohol)
- MRI is more sensitive than CT for early ischaemic stroke (86-100% vs 48% < 1 day) and for optic nerve/posterior fossa pathology, but CT is first-line in acute stroke to exclude haemorrhage
High Yield Summary — Management of Acute Visual Loss
- GCA: Start high-dose steroids IMMEDIATELY upon clinical suspicion. IV methylprednisolone if visual symptoms present. Do NOT wait for biopsy. Taper slowly over 1-2 years. Tocilizumab as steroid-sparing agent. Dramatic response within 48-72 hours expected
- AACG: Multiple agents to lower IOP (timolol + apraclonidine + acetazolamide ± pilocarpine ± mannitol). Definitive: laser peripheral iridotomy (PI). Fellow eye prophylactic PI
- CRAO: Ocular massage, AC paracentesis, consider thrombolysis if early. Most importantly: vascular workup like a stroke (carotid Doppler, ECG, echo, antiplatelet, statin)
- Retinal detachment: Surgical emergency. PPV, scleral buckle, or pneumatic retinopexy. "Macula-on" = urgent within 24 hours
- Optic neuritis: IV methylprednisolone 1g/day x 3 days → oral taper. Oral steroids ALONE are contraindicated (↑recurrence). Hastens recovery but does NOT change long-term visual outcome. MRI for MS workup
- Wet AMD: Intravitreal anti-VEGF (ranibizumab, aflibercept, bevacizumab). Monthly or treat-and-extend
- Diabetic retinopathy: Risk factor control for early stages. PRP for severe NPDR and PDR. Anti-VEGF for macular oedema and neovascularization. Vitrectomy for VH and tractional RD
- Vitreous haemorrhage: Observation if mild (blood clears ~1%/day). Vitrectomy if non-clearing, associated RD, or rubeosis
- PRP complications: pain, poor night vision, VF loss, VA loss — these are acceptable trade-offs to save central vision
- Methanol: Fomepizole (or ethanol) + haemodialysis + folic acid. Block alcohol dehydrogenase, remove toxin, enhance formate metabolism
High Yield Summary — Complications of Acute Visual Loss
- CRAO complications: neovascularization (2-3 months), neovascular glaucoma (up to 18%), vitreous haemorrhage. CRAO is a stroke equivalent — subsequent stroke and MI are the most important systemic complications
- CRVO: "90-day glaucoma" — neovascular glaucoma from ischaemic CRVO developing ~3 months post-occlusion via VEGF-driven rubeosis iridis
- GCA: bilateral permanent blindness (fellow eye at 50% risk if untreated), aortic aneurysm/dissection (17× risk), posterior circulation stroke. Steroid side effects are a major management consideration
- Retinal detachment: irreversible vision loss if macula detached > 24 hours. PVR (8-10%) is the most common cause of failed RD surgery
- AACG: permanent glaucomatous optic neuropathy, chronic angle closure from PAS, fellow eye attack if prophylactic PI not performed
- Optic neuritis: progression to MS (50% at 15 years), recurrence (35% at 10 years), optic atrophy
- Diabetic retinopathy complications causing acute visual loss: vitreous haemorrhage, tractional RD, neovascular glaucoma, diabetic macular oedema
- Treatment complications: PRP causes night vision loss and VF loss (trade-off); anti-VEGF risks endophthalmitis; vitrectomy accelerates cataract; gas tamponade contraindicated with flying and nitrous oxide
- Drug-induced: ethambutol → optic neuritis (worse with renal impairment); hydroxychloroquine → bull's eye maculopathy (screen annually after 5 years)
- Diabetic CN III palsy is pupil-sparing because ischaemia affects the core motor fibres (central in the nerve), while the pupillary parasympathetic fibres run on the surface and receive separate blood supply
Red Eye
Red eye is a common clinical sign characterized by hyperemia of the conjunctival, episcleral, or ciliary vessels due to a wide range of conditions including conjunctivitis, uveitis, acute glaucoma, corneal disorders, or subconjunctival hemorrhage.
Chronic Vision Loss
Chronic vision loss is a gradual, progressive decline in visual acuity or visual field occurring over weeks to years, commonly caused by conditions such as cataracts, glaucoma, macular degeneration, or diabetic retinopathy.