Cornea
This section covers corneal anatomy, dystrophies, infection, transplantation, and refractive surgery. The exam tests pattern recognition, emergency decisions, and when to avoid steroids.
Core rules and concepts
- The cornea has epithelium, Bowman layer, stroma, Descemet membrane, and endothelium; endothelial pump failure causes stromal oedema.
- Keratoconus shows inferior steepening, irregular astigmatism, Fleischer ring, Vogt striae, and scissoring on retinoscopy; corneal cross-linking is considered for documented progression.
- Fuchs endothelial dystrophy causes guttata and morning visual blur; endothelial keratoplasty is preferred when the stroma is still clear.
- Microbial keratitis requires corneal scraping and intensive topical antibiotics; fungal ulcers need antifungal therapy and often have feathery margins, satellite lesions, and hypopyon.
- A positive Seidel test indicates full-thickness corneal perforation.
Worked example
A soft contact-lens wearer presents with a painful red eye, a 2 mm epithelial defect, stromal infiltrate, and hypopyon. The likely organism is Pseudomonas aeruginosa. Management is immediate lens removal, corneal scraping for stains and culture, and intensive topical fluoroquinolone or fortified antibiotics. Steroids are withheld until infection is controlled. Daily review is mandatory because pseudomonal keratitis can progress to perforation within 24–48 hours.
Traps that cost marks
Prescribing topical steroids for a dendritic ulcer can worsen herpes simplex keratitis. Missing an AC reaction or hypopyon underestimates severity. Do not diagnose keratoconus from topography alone without clinical signs. In perforation, avoid pressure on the globe and arrange urgent tectonic cover.