Cornea and External Disease
Core concepts
Know the corneal layers and their diseases: epithelial (recurrent erosion, dry eye), stromal (keratoconus, dystrophies), endothelial (Fuchs). Understand the causes of red eye: conjunctivitis (viral, bacterial, allergic), keratitis, uveitis, acute angle closure, scleritis, and episcleritis. Differentiate by discharge, pain, photophobia, and visual acuity.
Know the management of dry eye (artificial tears, punctal plugs, cyclosporine), keratoconus (spectacles, rigid lenses, cross-linking, keratoplasty), and corneal ulcers (scraping, targeted antibiotics). Recognize pterygium, pinguecula, and their indications for surgery.
Traps
- Assuming all red eyes are conjunctivitis.
- Missing acute angle closure (fixed dilated pupil, halos, severe pain).
- Forgetting that viral conjunctivitis is highly contagious and self-limiting.
- Confusing keratoconus (inferior steepening) with pellucid marginal degeneration (inferior band).
Rule of thumb
Pain + photophobia + reduced vision = serious (keratitis, uveitis, angle closure), not simple conjunctivitis.
Worked example
A contact lens wearer presents with severe pain and a corneal infiltrate. Treat as bacterial keratitis: scrape, start fluoroquinolone, and stop lens wear.