Cornea and External Eye Disease
Core concepts
Know corneal anatomy (epithelium, Bowman, stroma, Descemet, endothelium) and physiology (deturgescence, tear film). Recognise keratitis patterns: bacterial, viral (dendritic), fungal, and acanthamoeba. Understand dry eye disease, blepharitis, and ocular surface inflammation. Learn corneal dystrophies (Fuchs, lattice, granular) and ectasias (keratoconus). Know the principles of corneal transplantation (penetrating versus lamellar) and graft rejection signs. Understand contact lens complications and when to culture.
Traps
Questions test distinguishing epithelial defects from stromal involvement; a dendritic ulcer is herpes simplex, not zoster. Remember the endothelium does not regenerate; Fuchs dystrophy causes guttae and oedema. Distinguish marginal keratitis from infectious ulcer. Acanthamoeba is associated with contact lens use and severe pain out of proportion to signs.
Worked example
A contact lens wearer presents with severe pain and a ring infiltrate. Suspect acanthamoeba keratitis; obtain corneal scraping and start appropriate therapy. Rule of thumb: pain out of proportion to signs in a lens wearer suggests acanthamoeba.