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.