Corneal microsporidiosis - Report of case, including electron microscopic observations

Objective: To report a case of corneal stromal infection caused by a protoz oon of the genus Microsporidia, including clinical, histopathologic, and el ectron microscopic observations. Design: Case report. Methods: Light and electron microscopy studies were performed on keratectom y specimens from a 67-year-old immunocompetent man who had a unilateral chr onic stromal keratitis that was refractory to medical treatment, Initial co rneal biopsy followed by lamellar and penetrating keratoplasty were perform ed on the patient. All the specimens were studied histopathologically. Results: Light microscopy of the corneal biopsy and the subsequent keratect omy specimens demonstrated myriad small, round to oval microsporidial organ isms measuring 3.5 to 5.0 mu m in length that stained positively with the p eriodic acid-Schiff, Grocott-methenamine silver, and acid-fast methods and were gram positive. Electron microscopic observations demonstrated viable b lastospores that had a thin osmiophilic outer cell wall and contained 11 to 13 coils of the filament. The light and electron microscopic features, the tinctorial characteristics, and the selective corneal stromal involvement ave consistent with microsporidial keratitis. Conclusions: Microsporidiosis should be considered in the differential diag nosis of a culture-negative stromal keratitis refractory to medical treatme nt. The diagnosis can be easily established based on the morphologic featur es of the protozoa in the keratectomy specimens. No effective medical treat ment for the stromal disease is available. Full-thickness keratoplasty is s uggested because, in our patient, lamellar keratoplasty did not preclude re currence of the disease. Ophthalmology 2000; 107:1769-1775 (C) 2000 by the American Academy of Ophthalmology.