Nosematosis of the cornea. Case report, including electron microscopic studies.

A 26-year-old woman underwent enucleation of a blind, painful eye because of a perforated corneal ulcer. Histopathologic examination of the eye disclosed an acute, necrotizing keratitis surrounding myriad small (2.5 to 3 x 4.5 to 5 micrometer), oval, faintly visible structures. Under polarized light, they were partially birefringent and stained intensely positive with the acid-fast technique. The organisms were located mainly within the cytoplasm of histiocytes in the deep corneal lamellae. They were interpreted as a protozoa of the genus Nosema. The diagnosis was confirmed by electron microscopic studies. The distinguishing features between Nosema species and Encephalitozoon are discussed. To our knowledge, this is the second documented case of corneal nosematosis.