External Disease and Anterior Segment
This section covers external disease and the anterior segment: red-eye differential diagnosis, eyelid margin disease, dry eye, conjunctivitis, pterygium, and herpetic disease. The exam tests safe triage of common presentations.
Core rules and concepts
- Bacterial conjunctivitis is usually bilateral, purulent, and self-limited; gonococcal disease is hyperacute and needs systemic ceftriaxone.
- Viral conjunctivitis is watery, often unilateral then bilateral, with preauricular adenopathy; adenovirus is highly contagious.
- Blepharitis is treated with lid hygiene and warm compresses; rosacea adds oral doxycycline or topical azithromycin.
- Dry eye is assessed with tear breakup time, ocular surface staining, and meibomian gland evaluation; preservative-free tears are preferred in frequent users.
- Herpes simplex keratitis classically shows a dendritic ulcer with terminal bulbs; herpes zoster ophthalmicus requires oral antivirals and urgent referral if Hutchinson sign is present.
Worked example
A 35-year-old has a painful red eye, photophobia, and a branching corneal epithelial lesion with terminal bulbs after a febrile illness. The diagnosis is herpes simplex epithelial keratitis. Treatment is topical ganciclovir or trifluridine; topical corticosteroid alone is contraindicated because it promotes viral replication and stromal disease. Fluorescein staining confirms the dendrite. The patient is reviewed in 2–3 days, and steroid is added later only for immune stromal keratitis under antiviral cover.
Traps that cost marks
Calling every red eye bacterial conjunctivitis misses sight-threatening uveitis, keratitis, and acute glaucoma. Do not use steroids for undiagnosed dendritic ulcers. Hutchinson sign in herpes zoster ophthalmicus predicts nasociliary involvement and ocular risk. Pterygium excision is not urgent unless it threatens the visual axis.