Always test each eye separately ^[1]

Why VA is the "vital sign" of the eye: Just as blood pressure quantifies cardiovascular function, VA quantifies the entire visual pathway — from cornea to occipital cortex. An abnormal VA tells you something is wrong; the pattern of abnormality tells you where.

Snellen Chart:

6/6 vision is defined as the ability to resolve two points separated by a visual angle of one minute of arc (1/60 of a degree). ^[1]

• The notation "6/X" means: at 6 metres, the patient reads a letter that a normal eye reads at X metres.
• 6/6 = normal; 6/12 = the patient needs to be at 6 m to read what normal sees at 12 m — moderate reduction.

Why the Snellen system works: Letters of different sizes subtend different visual angles at 6 m. The smallest line where each letter subtends exactly 5 arcminutes (with each stroke 1 arcminute) is the 6/6 line.

WHO Criteria for Vision Impairment Severity: ^[1]

Recording VA worse than 3/60: When a patient cannot read even the largest Snellen letter at 3 m, record descending levels:

1. Counting Fingers (CF) — at specified distance (e.g., CF at 1 m)
2. Hand Movements (HM) — can perceive a moving hand
3. Light Perception (LP) — can detect a light source
4. No Light Perception (NLP) — total blindness

How do you know the refractive error is under-corrected? → Pinhole visual acuity ^[1]

Why it works from first principles: A pinhole (1.5 mm aperture) blocks peripheral rays, allowing only para-axial rays to reach the retina. This eliminates refractive blur (myopia, hyperopia, astigmatism) because the small aperture creates a nearly infinite depth of focus.

RAPD — Relative Afferent Pupillary Defect ^[1]

• Ask patient to look to the distance
• Look at the eye you are examining
• Swing from one eye to another
• Looking for reactions — change in size from small to big (dilate) or big to small (constriction)

The Swinging Flashlight Test — Why it works:

The pupillary light reflex is a bilateral, consensual reflex. Light in one eye constricts both pupils equally because the signal crosses at the optic chiasm and pretectal nuclei. When you swing the light from the normal eye to an eye with optic nerve damage:

• The total afferent input drops
• Both pupils therefore dilate (paradoxical dilation of the affected eye when light swings onto it)
• This is the RAPD or "Marcus Gunn pupil"

What does a relative afferent pupillary defect indicate? → Asymmetric optic nerve or retinal disease on the side of the RAPD ^[1]

Key clinical points about RAPD:

• It indicates a unilateral or asymmetric lesion of the optic nerve (or extensive retinal disease)
• It does NOT occur in: cataract alone, uncorrected refractive error, amblyopia (these do not damage the afferent pathway)
• It DOES occur in: optic neuritis, ischaemic optic neuropathy, glaucoma (advanced unilateral), central retinal artery occlusion (extensive retinal damage), compressive optic neuropathy

Can a patient with bilateral optic neuropathy be associated with an RAPD? ^[1] Answer: YES — if the damage is asymmetric. A patient with bilateral optic neuritis but one side worse than the other will have an RAPD in the worse eye. If damage is perfectly symmetrical, there will be no RAPD (because "relative" means comparing one side to the other).

How to report optic disc examination findings: ^[1]

1. Margin: clear or blurred
2. Neuroretinal rim colour: pink or pale
3. Vertical cup-to-disc ratio

This structured reporting is what examiners expect in OSCE and written answers.

Why each component matters:

Direct vs Indirect Ophthalmoscopy:

Direct ophthalmoscopy / Indirect ophthalmoscopy ^[1]

Confrontation visual field testing is a bedside screening tool. Each eye is tested separately. The examiner compares the patient's visual field to their own (assuming normal fields). This detects:

• Peripheral field loss (glaucoma, retinal detachment)
• Hemianopias (stroke, pituitary tumour)
• Central scotomas (macular disease, optic neuritis)

Tests CN III (SR, IR, MR, IO + LPS), CN IV (SO), CN VI (LR). Diplopia, restriction, or nystagmus may indicate cranial nerve palsy (e.g., diabetic mononeuropathy), thyroid eye disease, or orbital pathology.

Differential Diagnosis of a pale neuroretinal rim (optic neuropathy): ^[1]

Signs of optic disc swelling: ^[1]

• Blurred optic disc margin
• Hyperaemia — dilation of the disc capillaries
• Haemorrhage: nerve fibre layer or retinal haemorrhages
• Dilation and tortuosity of retinal veins
• Soft exudates or cotton wool spots

Why each sign occurs:

• Blurred margin: Axonal swelling from impaired axoplasmic flow (due to raised pressure, inflammation, or ischaemia) causes the nerve fibres at the disc edge to swell and obscure the margin
• Hyperaemia: Vascular engorgement from impaired venous drainage
• Haemorrhages: Rupture of small peripapillary vessels under pressure
• Venous dilation/tortuosity: Back-pressure from impaired venous return
• Cotton wool spots: Ischaemic infarcts of the nerve fibre layer (retinal arteriolar occlusion → ganglion cell ischaemia)

Differential Diagnosis of Optic Disc Swelling: ^[1]

Glaucoma, a neurodegenerative disease of the optic nerve, is the leading cause of irreversible blindness worldwide. ^[1] With 76 million glaucoma patients in 2020 worldwide, the need for early detection is pressing. ^[1]

Why glaucoma is a "silent" disease:

Glaucoma patients are not aware of visual impairment/blindness even at the advanced stages! ^[1]

This is because:

1. Glaucoma preferentially damages peripheral visual field first (mid-peripheral arcuate scotomas)
2. The brain fills in the missing visual field using the other eye and surrounding field (completion phenomenon)
3. Central VA is preserved until very late stages
4. There is no pain in chronic open-angle glaucoma

Diagnosis:

1. Glaucoma is a chronic progressive optic neuropathy. ^[1] 2. Clinical diagnosis of glaucoma is predicated on the detection of a thinned retinal nerve fibre layer (RNFL) and narrowed neuroretinal rim. (World Glaucoma Association Consensus Statement) ^[1]

This means glaucoma is diagnosed by structural damage to the optic nerve, NOT by intraocular pressure (IOP) alone. IOP is the major modifiable risk factor, but:

• Some patients have glaucoma with normal IOP ("normal tension glaucoma")
• Some patients have high IOP without glaucoma ("ocular hypertension")

Current standard for detection and monitoring:

Structure: Optical coherence tomography (OCT) is the prevailing technology to detect retinal nerve fibre layer (RNFL) thinning. ^[1] Function: Visual field testing determines the extent of functional loss. ^[1]

Cataract ^[1] — Examined by slit lamp examination

What is a cataract? Opacification of the crystalline lens. It is the most common cause of reversible blindness worldwide and the most common cause of visual impairment overall.

Why cataracts form:

• Age-related (most common): Cumulative oxidative damage → protein denaturation and aggregation in lens fibres → loss of transparency
• Diabetic: Hyperglycaemia activates the polyol (sorbitol) pathway via aldose reductase → sorbitol accumulates in lens → osmotic swelling → lens fibre disruption ^[3]
• Steroid-induced: Posterior subcapsular cataract — glucocorticoids alter lens epithelial cell metabolism
• Traumatic, congenital, radiation-induced

Types:

Diagnosis: Slit lamp examination — look for lens opacity, assess red reflex (diminished or absent in dense cataract)

Management: Surgical removal (phacoemulsification) with intraocular lens (IOL) implant when VA impairs function. There is no effective medical treatment.

Undercorrected refractive error ^[1] — the most common cause of visual impairment globally (the answer to the opening poll question)

Types of refractive error:

Complications related to myopia: ^[1]

• Glaucoma
• Retinal detachment
• Myopic choroidal neovascularization
• Myopic macular atrophy

Why myopia predisposes to these complications: In myopic eyes, the axial length is increased → the retina is stretched thinner → peripheral retinal degeneration → tears/holes → retinal detachment. The vitreous is also more liquefied → posterior vitreous detachment occurs earlier. The optic nerve head is larger and more susceptible to glaucomatous damage. Scleral stretching at the macula causes macular atrophy.

Complications related to hyperopia: ^[1]

• Primary angle-closure glaucoma

Why hyperopia predisposes to angle-closure: Hyperopic eyes are shorter → the anterior chamber is shallower → the peripheral iris is closer to the trabecular meshwork → the angle is narrower → risk of pupillary block (when the mid-dilated pupil apposes the lens, aqueous cannot flow from posterior to anterior chamber → iris bows forward → angle closes → IOP spikes).

Distinguishing refractive error from other causes of poor VA:

Pinhole visual acuity — if VA improves with pinhole, refractive error is the cause. ^[1]

The lecture shows sequential images of a scene through varying refractive errors vs through a cataract vs corrected. The key teaching point is that both cataract and refractive error blur vision, but:

• Refractive error: correctable with pinhole or proper refraction
• Cataract: only partially improved with pinhole; requires surgical correction

Age-related macular degeneration ^[1]

Two types:

Dry AMD — geographic atrophy and drusen ^[1] Wet AMD — treated with anti-VEGF intravitreal injection ^[1]

Clinical presentation:

• Gradual painless central visual loss
• Metamorphopsia — distortion of straight lines (detected with Amsler grid)

Amsler Grid — metamorphopsia ^[1]

Why metamorphopsia occurs: Subretinal fluid or neovascular membrane lifts and distorts the photoreceptor arrangement at the macula → straight lines appear wavy. This is a red flag for wet AMD — needs urgent ophthalmology referral.

Why anti-VEGF works: In wet AMD, ischaemic retina and RPE upregulate VEGF → drives choroidal neovascularization. Intravitreal anti-VEGF (e.g., ranibizumab, aflibercept) blocks VEGF → prevents new vessel growth and reduces leakage → stabilizes or improves vision. ^[4]

Diabetic retinopathy ^[1]

DR is covered in detail in the GC 042 lecture. Key points from this lecture and supporting sources:

Pathophysiology (from first principles): ^{[3] [5]}

1. Chronic hyperglycaemia → metabolic damage to retinal capillary pericytes and endothelial cells
2. Microangiopathy: Loss of pericytes → microaneurysm formation → dot-and-blot haemorrhages
3. Capillary leakage: Breakdown of blood-retinal barrier → hard exudates (lipoprotein deposits) → retinal oedema
4. Ischaemia: Capillary occlusion → cotton wool spots (nerve fibre layer infarcts) → venous beading → IRMA (intraretinal microvascular abnormalities)
5. Neovascularization: Ischaemia → VEGF upregulation → new fragile vessels grow (proliferative DR) → vitreous haemorrhage → tractional retinal detachment

Classification:

Important ocular complications of DM (beyond retinopathy): ^[3]

• Diabetic macular oedema (commonest cause of vision loss in DM)
• Neovascular glaucoma — rubeosis iridis (new vessels on iris → angle closure)
• CN III, IV, VI palsies (diabetic mononeuropathy)
• Cataract (sorbitol accumulation)
• ↑ eye infections

Subconjunctival haemorrhage ^[1]

• Bleeding from small conjunctival/episcleral vessels → bright red, flat discolouration of the sclera
• Painless, no visual disturbance, no photophobia
• Usually self-limiting (resolves in 7–14 days) ^[4]
• Causes: idiopathic (most common), minor trauma (rubbing), hypertension, coagulopathy/anticoagulants, Valsalva (coughing, straining), conjunctivitis
• No treatment needed — reassurance
• Check BP and bleeding history if recurrent ^[4]

Pterygium ^[1]

• Triangular fibrovascular growth of conjunctiva that extends onto the cornea (from nasal side, toward centre)
• UV exposure is the major risk factor (hence more common in tropical/equatorial regions)
• Can cause astigmatism, visual obstruction if it encroaches on the visual axis
• Management: observation for mild cases; surgical excision with conjunctival autograft if threatening visual axis or causing significant astigmatism (recurrence rate is high without graft)

Dry eye disease — punctate epithelial erosion ^[1]

The tear film has three layers:

1. Lipid layer (outermost) — produced by Meibomian glands (tarsal glands) → prevents evaporation
2. Aqueous layer (middle) — produced by lacrimal gland → provides lubrication, nutrients, antimicrobial factors
3. Mucin layer (innermost) — produced by conjunctival goblet cells → allows aqueous layer to adhere to corneal epithelium

Dry eye disease occurs when:

• Aqueous deficiency: Reduced lacrimal gland secretion (e.g., Sjögren's syndrome, ageing, post-radiation)
• Evaporative: Meibomian gland dysfunction (most common cause), blepharitis, reduced blink rate (screen use)
• Mucin deficiency: Damage to goblet cells (e.g., chemical burns, cicatricial pemphigoid, Stevens-Johnson syndrome)

Symptoms: Gritty/sandy sensation, burning, foreign body sensation, paradoxical tearing (reflex watering), worse in dry/windy environments

Signs: Punctate epithelial erosions (seen with fluorescein staining under cobalt blue light), reduced tear break-up time ( < 10 seconds), low Schirmer's test ( < 5 mm in 5 minutes)

Management: Artificial tears, warm compresses for MGD, punctal plugs in severe cases, cyclosporine A drops for inflammatory dry eye

Meibomian gland dysfunction ^[1]

• The most common cause of evaporative dry eye
• Meibomian glands (sebaceous glands in the tarsal plate) produce the lipid layer of the tear film
• Obstruction → lipid deficiency → rapid tear film evaporation → dry eye
• Associated with blepharitis, rosacea
• Treatment: warm compresses, lid hygiene, omega-3 fatty acids, topical antibiotics (azithromycin) if associated blepharitis

Floaters ^[1]

What floaters are: Shadows cast on the retina by opacities in the vitreous humour. They move with eye movement and are most noticeable against bright backgrounds.

Common causes:

• Posterior vitreous detachment (PVD): Most common cause in adults > 50. The vitreous shrinks and separates from the retina → collagen fibres clump → cast shadows. Usually benign.
• Vitreous haemorrhage: Sudden shower of floaters → think DR, retinal tear
• Inflammatory cells (vitritis): In posterior uveitis
• Retinal tear or detachment: Floaters + flashes of light (photopsia) = RED FLAG

Retinal tear with detachment ^[1]

Why this is an emergency: Once the retina detaches from the underlying RPE, photoreceptors lose their blood supply and undergo irreversible degeneration. If the macula is involved ("macula-off"), prognosis for visual recovery is significantly worse.

Pathophysiology:

1. PVD → vitreous traction on retina → retinal tear
2. Liquefied vitreous flows through the tear → separates sensory retina from RPE → rhegmatogenous retinal detachment

Symptoms:

• New floaters (sudden onset, shower of spots)
• Flashes of light (photopsia) — caused by vitreous traction stimulating the retina mechanically
• "Curtain" or shadow descending across visual field — as detachment progresses

Risk factors: High myopia, prior eye surgery, trauma, lattice degeneration, family history, PVD

Management: Urgent ophthalmological referral. Surgical repair options include:

• Laser photocoagulation / cryotherapy (for tears without detachment)
• Pneumatic retinopexy, scleral buckle, or pars plana vitrectomy (for detachment)

The Red Eye lecture classifies red eye by location and urgency. Key discriminators for the exam:

The top five causes of chronic visual loss globally:

1. Uncorrected refractive error
2. Cataract
3. Glaucoma
4. AMD
5. Diabetic retinopathy

These are exactly the five diseases covered in this CFB lecture.

2021 Fourth Summative MCQ Q13: A 54-year-old lady on hydroxychloroquine for 8 years complains of bilateral progressive blurring of vision. Most likely cause = C. Bull's eye maculopathy ^[7]

Hydroxychloroquine accumulates in the RPE → damage to photoreceptors → characteristic ring of RPE depigmentation around the fovea ("bull's eye"). Risk increases with cumulative dose (> 5 years or > 5 mg/kg/day). Annual screening with OCT and visual field testing is recommended after 5 years of use.

2017 Fourth Summative SAQ Q3: A 30-year-old woman with "sand in eye" sensation and xerostomia, anti-Ro/anti-La positive → Sjögren's syndrome ^[8]

Sjögren's causes keratoconjunctivitis sicca (dry eye from lacrimal gland lymphocytic infiltration) and xerostomia (dry mouth from salivary gland infiltration). ^[9]