Anterior Segment and Cornea
Core concepts
Master the layers of the cornea and what each contributes to disease. Epithelial disease produces punctate staining and rapid turnover; stromal disease produces haze, scarring, and vascularization; endothelial failure produces edema that is worse on waking. Know the corneal dystrophies by layer (epithelial basement membrane, Reis-Bücklers, lattice, granular, macular, Fuchs, posterior polymorphous) and their inheritance. Understand microbial keratitis risk factors: contact lens wear (especially Pseudomonas), trauma with vegetative matter (Fusarium, Aspergillus), and contact lens-related Acanthamoeba with ring infiltrate and severe pain out of proportion. Know the signs of herpetic disease: dendritic ulcer with terminal bulbs, reduced corneal sensation, and the trap of treating a geographic ulcer with topical steroid alone.
Traps
Questions love to test which layer is involved. A patient with recurrent erosions after trauma has epithelial adhesion failure, not stromal disease. Another trap: distinguishing marginal keratitis (sterile, hypersensitivity to staphylococcal antigen, responds to steroid plus lid hygiene) from infectious ulcer (needs scraping and antibiotics). Also know when to avoid steroids: active bacterial or fungal infection, and dendritic ulcer.
Worked example / rule of thumb
A soft contact lens wearer presents with a painful red eye and a white infiltrate. Think Pseudomonas first; treat with fluoroquinolone and remove the lens. If there is a ring infiltrate and pain is severe, consider Acanthamoeba and obtain confocal microscopy or culture. Rule of thumb: for any corneal ulcer, scrape before treating, and never start steroids until you have ruled out active infection.