Cornea and External Disease
Concept anchors
Structure drives management: epithelium regenerates, stroma scars, endothelium is finite. For any corneal ulcer, scrape before treating, send cultures and consider confocal microscopy. Bacterial ulcers (pneumococcus, Pseudomonas in contact lens wearers) are acute and suppurative; fungal ulcers follow vegetable-matter trauma and show feathery margins and satellite lesions; Acanthamoeba occurs with contact lenses and tap water, with radial keratoneuritis and ring infiltrate; herpes simplex gives a branching dendrite with terminal bulbs, best confirmed by PCR.
Traps
Giving steroids before a scrape is a classic error, as is missing herpes zoster ophthalmicus (Hutchinson sign, nasociliary involvement) and delaying antivirals. Distinguish a dendrite from the pseudodendrite of Acanthamoeba or healing abrasion. Recurrent corneal erosion follows trauma or epithelial basement membrane dystrophy; treat with lubricants, then diamond burr or superficial keratectomy. Keratoconus shows inferior steepening, Vogt striae, Fleischer ring and Munson sign; cross-linking arrests progression.
Endothelial and surgical disease
Fuchs dystrophy shows guttae and gradual decompensation; DMEK replaces endothelium with better outcomes than DSAEK, while DALK preserves host endothelium and lowers rejection risk. Graft rejection presents with an endothelial rejection line, keratic precipitates, circumcorneal injection and falls in acuity - treat with intensive topical and sometimes systemic steroid.
Worked rule of thumb
Chemical injury: irrigate immediately with litres of saline, check pH until neutral, then manage ischemia and inflammation. Peripheral ulcerative keratitis warrants systemic workup for rheumatoid arthritis and vasculitis, not just topical therapy. Mooren ulcer is a diagnosis of exclusion.