Case 1: 85/F living alone ^[1]:

• PMH: dry eyes on lubricating eyedrops
• One hour ago, both eyes (OU) very painful after putting "usual eyedrops"
• Rinse with tap water
• Immediate action: Irrigate and check pH

This case illustrates accidental chemical exposure — an elderly patient mistakenly used a chemical agent instead of her lubricating drops. The clinical lesson: always irrigate first, ask questions later.

Chemical burn of the eye — epidemiology ^[1]:

• Workplace injuries: predominantly young men
• Household injuries: predominantly young children (1–2 years old)

Severity of injury depends on ^[1]:

1. Chemical: type (acid vs alkali) and concentration
2. Duration of exposure: time from injury to first aid (irrigation)
3. Area of involvement
4. Depth of penetration

A specific high-yield example from the slides: Cement/concrete has pH 12–14 (containing lime / calcium hydroxide) — this is an alkali and therefore extremely dangerous ^[1].

Acid burn vs Alkali burn ^[1]:

Fluorescein stain + Cobalt blue light ^[1]:

Fluorescein is a vital dye that stains areas of epithelial loss. When viewed under cobalt blue light, denuded epithelium fluoresces bright green. This is how you map the extent of corneal epithelial damage in chemical burns (and corneal abrasions, ulcers, etc.).

The slide also shows clinical photos of "At presentation" vs "Day 3 treatment" — demonstrating the evolution of healing (or worsening) after appropriate management ^[1].

Emergency management ^[1]:

• Immediate copious irrigation (do not wait)
• Aim to eliminate the causative agent
• Target pH 7.0–7.2
• Wait 5–10 minutes then recheck pH

Practical irrigation tips:

• Use at least 1–2 litres of fluid per eye
• Evert the eyelids to irrigate the fornices (where chemical particles lodge)
• Use topical anaesthetic drops first if available — this reduces blepharospasm and allows better irrigation
• In alkali burns, you may need to irrigate for 30–60 minutes or more
• Continue until pH is stable at 7.0–7.2 on two consecutive checks 5–10 minutes apart

Roper-Hall Classification ^[1]:

Why limbal ischaemia matters: The limbus houses the limbal stem cells that regenerate the corneal epithelium. More limbal ischaemia = fewer surviving stem cells = worse epithelial healing potential = worse prognosis. In Grade IV, the limbus is so ischaemic that the cornea will not heal on its own → the eye may eventually need a limbal stem cell transplant, keratoplasty, or even end up phthisical (shrunken, non-functional).

The slide also references Dua et al. (Eye 2020) which provides a more detailed classification system based on limbal involvement (in clock hours) and conjunctival involvement (percentage), and notes that limbal stem cells provide circumferential healing ^[1].

Beyond the emergency phase, management of chemical burns includes:

• Topical antibiotics (prevent secondary infection of denuded epithelium)
• Topical steroids (reduce inflammation — used cautiously, taper by day 10–14 to avoid inhibiting collagen synthesis)
• Topical cycloplegics (e.g., atropine — reduces ciliary spasm/pain, prevents posterior synechiae)
• Ascorbate (topical and/or oral — promotes collagen synthesis, improves wound healing)
• Citrate (chelates calcium, reduces PMN activity)
• Doxycycline (systemic — MMP inhibitor, reduces collagenolysis)
• Amniotic membrane transplantation (for severe burns, Grade III–IV)
• Limbal stem cell transplantation (for limbal stem cell deficiency in the chronic phase)

Full thickness wound ^[1]:

• Laceration: caused by a sharp object
• Rupture: caused by blunt force

This is the fundamental distinction in open globe injuries. A laceration has a clean, well-defined wound from a sharp instrument (knife, glass, wire). A rupture occurs when blunt force (e.g., fist, ball, fall) raises intraocular pressure to the point that the globe wall gives way at its weakest point.

Blunt force ^[1]:

• Results in peripheral volume displacement with increased "wedge pressure"
• The area of least resistance is most affected:
  • Lens (zonular dehiscence → subluxation/dislocation)
  • Iris root (iridodialysis)
  • Trabecular meshwork (traumatic glaucoma)
  • Retina at vitreous base (retinal dialysis → detachment)
  • Thinnest sclera posterior to muscle insertion (rupture site)

Why the sclera is thinnest behind muscle insertions: The extraocular muscles insert into the sclera, and just posterior to these insertions the sclera is at its thinnest (approximately 0.3 mm). When intraocular pressure suddenly spikes from a blunt hit, the globe wall blows out at this weakest point, often producing a scleral rupture that is hidden behind the equator and not visible on external examination. This is why a "normal-looking" eye after blunt trauma can still be an open globe injury.

Assessment of ocular mechanical trauma ^[1]:

Is it likely to be an open globe injury? Consider:

• Mechanism of injury: sharps, high impact force, severe injury (e.g., multiple trauma, serious head injuries)
• Foreign body in high-velocity injuries (e.g., hammering, drilling, explosion)
• Risk factors: prior eye surgeries (old surgical wounds are weak points), lack of protective eyewear, contamination

Physical examination may not always be feasible at bedside ^[1]:

• Difficult if soft tissue swelling, profuse bleeding, or pain → do not force open
• Must be very gentle
• Avoid manipulation that exerts pressure on the eye (e.g., lid retraction, putting lid speculum, direct contact with globe)
• Do not remove any protruding foreign body or tissues from the eye

Signs of open globe ^[1]:

• Obvious corneal or scleral lacerations
• Uveal prolapse (dark brown/black tissue protruding through the wound — this is iris/ciliary body/choroid)
• Peaked pupil (iris tissue plugging the wound distorts the pupil toward the laceration site)
• Volume loss (the eye is soft/hypotonus because aqueous/vitreous has leaked out)
• Protruding foreign body
• Bullous subconjunctival haemorrhage (may mask an underlying scleral rupture)

Other signs of ocular injury ^[1]:

• Hyphaema: blood in the anterior chamber (visible as a fluid level or diffuse red tinge)
• Iridodialysis: disinsertion of the iris root from the ciliary body
• Lens subluxation/dislocation: disrupted zonular fibres → lens shifts or falls into vitreous
• Aphakia: absence of the lens (traumatic extrusion through wound or dislocation into vitreous)

Hyphaema deserves special mention: It is one of the most common findings in blunt ocular trauma. A small hyphaema (microhyphaema or < 1/3 anterior chamber) may resolve spontaneously. A total hyphaema (8-ball hyphaema) is a vision-threatening emergency because blood blocks aqueous outflow → acute IOP elevation → optic nerve damage, and blood staining of the cornea. Patients with sickle cell trait/disease are at particularly high risk of complications from even small hyphaemas because sickled red cells block the trabecular meshwork more easily.

Management of open globe injury ^[1]:

• Emergency ophthalmology consultation
• Urgent surgical repair within 24 hours

Pre-operative measures ^[1]:

• NPO (nil by mouth — patient needs general anaesthesia for repair)
• Bed rest — avoid cough or straining (any Valsalva raises IOP → may extrude intraocular contents)
• Pain management — reduces patient distress and involuntary straining
• Treat nausea and prevent vomiting — vomiting dramatically raises IOP
• ±Tetanus prophylaxis — especially for contaminated wounds, soil/vegetable matter
• Eye shield after initial examination — rigid, non-contact shield that protects the eye from inadvertent pressure

Eye shield: rigid, non-contact ^[1]

The eye shield is a critical concept: it is NOT an eye pad (soft gauze pad that contacts the eye). A rigid shield (e.g., a plastic or metal cup) rests on the bony orbital rim and does not touch the globe, preventing any external pressure that could worsen an open globe injury.

Additional pre-operative measures (from supporting sources) ^[2]:

• Systemic antibiotics (IV — to prevent endophthalmitis; the most devastating complication of open globe injury)
• Topical antibiotics (applied gently, without pressure)
• Anti-emetics (e.g., ondansetron)
• Elevate head of bed to reduce venous congestion

Blunt trauma to the orbit commonly causes orbital blowout fractures — the orbital floor (maxillary bone) and medial wall (lamina papyracea of the ethmoid) are the thinnest walls. Entrapment of the inferior rectus muscle in a floor fracture → restriction of upgaze → diplopia. On CT, you see a "trapdoor" defect in the orbital floor with herniation of orbital fat ± muscle into the maxillary sinus, and there may be a fluid level in the sinus (blood).

Clinical clues: infraorbital numbness (infraorbital nerve runs along the orbital floor), enophthalmos (sunken eye from expanded orbital volume), subcutaneous emphysema (communication with paranasal sinuses).

Retrobulbar haemorrhage after trauma can cause orbital compartment syndrome — a true ophthalmic emergency. The orbit is a closed bony cone; blood accumulating behind the globe raises intraorbital pressure → compresses the optic nerve and central retinal artery → irreversible blindness within 60–120 minutes.

Management: Lateral canthotomy and cantholysis — an emergency bedside procedure that releases the lateral canthal tendon, allowing the globe to prolapse forward and decompress the orbit. This is a procedure any emergency physician should know.

Blunt or penetrating injury can damage the optic nerve directly or indirectly (shearing forces transmitted through the orbital bones). Presents with decreased VA, RAPD, and impaired colour vision. High-dose IV methylprednisolone or surgical optic canal decompression may be considered (controversial).

The most feared complication of open globe injury. Bacterial or fungal infection of the vitreous cavity after penetrating trauma (especially with organic/vegetable matter). Presents with severe pain, decreased VA, hypopyon (pus in anterior chamber), vitritis. Requires emergency intravitreal antibiotics ± vitrectomy.

A rare but devastating bilateral granulomatous panuveitis that occurs days to years after penetrating trauma to one eye. The uninjured ("sympathizing") eye develops inflammation due to an autoimmune response against uveal antigens exposed by the trauma. This is why severely damaged eyes with no visual potential may be enucleated prophylactically (within 14 days of injury, ideally).

Stem: "A 70-year-old female with a history of hypertension and atrial fibrillation on direct oral anticoagulants presents to the general outpatient clinic with redness in her left eye for 2 days. She first noticed it when getting out of bed 2 days ago with no interval changes. She does not complain of any pain in the eye, headache, discharge, pruritis, or blurred vision. She does not recall any trauma or events leading up to it. On examination, her blood pressure is 135/85 mmHg. The lateral one-third of the eye is bright red. Visual acuity is normal. Bilateral pupils are equal and reactive to light. What is the MOST LIKELY diagnosis?"

Options: A. Acute angle closure glaucoma / B. Iritis / C. Retinal detachment / D. Subconjunctival haemorrhage

Answer: D. Subconjunctival haemorrhage

Rationale: Painless, bright red, no visual loss, normal pupils, on anticoagulants (risk factor for spontaneous subconjunctival haemorrhage). AACG would present with severe pain, decreased VA, mid-dilated non-reactive pupil. Iritis would have pain, photophobia, and cells/flare. Retinal detachment would have visual symptoms (flashes, floaters, curtain). This is a classic "benign" red eye that requires no emergent treatment.

Stem: "A 42-year-old woman presented with double vision. Her past health was good. Neurological examination revealed normal findings over first and second cranial nerves, normal eye movements in all directions, and normal findings over other cranial nerves... she noted double vision upon looking down and to the left; the upper image disappeared when her right eye was covered, and the lower image disappeared when her left eye was covered. CT brain was normal. Which extraocular muscle is affected?"

Options: A. Left inferior oblique / B. Left inferior rectus / C. Right medial rectus / D. Right superior oblique

Answer: D. Right superior oblique

Rationale: Diplopia worst looking down and to the left = testing the right superior oblique (SO depresses the eye when adducted). The image from the affected eye is higher (hypertropia of right eye). When the right eye is covered, the upper image disappears → confirming the right eye's image is the higher one → right SO palsy (CN IV). This is the classic Parks three-step test pattern.

Stem: "A man presented to the A&E with a stab wound, claimed to be inflicted by another individual. (a) List three features that must be recorded in the description of the stab wound. (6 marks) (b) List two features that help to differentiate self-inflicted injury from assault injury. (4 marks)"

Answer:

• (a) Site/location, length, depth, shape, edges (clean-cut vs irregular), direction/orientation, presence of underlying structure damage
• (b) Self-inflicted: hesitation marks (multiple superficial parallel cuts), accessible areas (wrists, forearms, anterior chest), non-dominant hand involvement. Assault: wounds on hands/forearms (defense wounds), deeper, irregular, in less accessible areas.

(This is relevant to the broader "Trauma and Ocular Emergency" topic cluster, testing wound description skills.)

Stem: "You are a team member of an Emergency Medical Team who responds to a mass casualty event. It involves an overturn of a double decker bus with more than 100 passengers extricated. To start, how would you rapidly differentiate those requiring emergency treatment and those who do not at scene?"

Options: A. Check all victims for normal pulsations of limbs / B. Check all victims for the ability to breathe normally / C. Check all victims for the ability to speak their names / D. Check all victims for the ability to walk to another area

Answer: D.

Rationale: In mass casualty triage (START triage), the first step is to ask all victims to walk — those who can walk are "walking wounded" (minor/green). This immediately separates a large group and allows you to focus on non-ambulatory patients.

No other past paper questions in the indexed context directly test the specific content of GC 126 (chemical burn classification, open globe signs, imaging in eye trauma). However, the above questions from the same exam series test closely related concepts.