Ocular Pathology and Microbiology
Core concepts
Know the basic categories of ocular pathology: inflammation, degeneration, dystrophy, neoplasia, and vascular disease. Understand the difference between hypertrophy, hyperplasia, metaplasia, and dysplasia. Recognise common corneal dystrophies (e.g., Fuchs endothelial dystrophy, lattice, granular) and their inheritance patterns.
Microbiology: distinguish bacterial, viral, fungal, and protozoal keratitis by risk factors and appearance. Bacterial ulcers are usually contact-lens related; fungal ulcers follow organic trauma; Acanthamoeba follows contact lens use with poor hygiene. Know Gram stain and culture principles. Understand that herpes simplex causes dendritic ulcers and is diagnosed clinically, with PCR or Giemsa for confirmation.
Traps
- Confusing dystrophy (bilateral, inherited) with degeneration (often bilateral but not inherited).
- Assuming all corneal ulcers need the same antibiotic.
- Forgetting that fungal ulcers may have a feathery border and satellite lesions.
- Mixing up the appearance of Acanthamoeba (ring infiltrate) with bacterial ulcer.
Rule of thumb
If the history includes organic matter trauma, think fungal; if contact lens with poor hygiene, think Pseudomonas or Acanthamoeba.
Worked example
A farmer presents with a corneal ulcer after a twig injury. Suspect fungal keratitis; obtain scraping for culture and start natamycin or voriconazole rather than a fluoroquinolone alone.