Histopathology of cornea (Periodic-acid Schiff stain, original magnification x 250)
Questions and Answers
1. What is the diagnosis? Answer: Fungal keratitis (Mycotic corneal ulcer)
2. What are the predisposing factors for developing this lesion? Answer: History of trauma particularly to vegetable matter or soil, a chronic preexisting ocular surface disorder, systemic and topical immunocompromise, and prolonged steroid use.
3. What are the stains used for demonstration of this lesion in paraffin fixed tissue? Answer: Gomori’s methenamine silver (GMS) stain in which the fungi stains black against a green background, and Periodic acid Schiff (PAS) stain in which the fungi stains vividly purple against a blue-gray background.
4. How do we treat this lesion? Answer: Anti-fungal medications. Penetrating keratoplasty is usually indicated for extensive lesions.