Clinical presentation and microbiological and histopathologic evidence of microsporidial stromal keratitis. A, Slitlamp picture showing corneal edema with Descemet folds during the initial visit. B, Clump of oval spores in the corneal scraping smear stained with calcofluor white and seen with a fluorescent microscope (original magnification ×400). C, Gram staining of corneal scraping showing intracellular and extracellular, oval, stippled, gram-positive, well-defined spores of microsporidia (original magnification ×1000). D, Slitlamp picture showing full-thickness stromal infiltrate with severe thinning. E, Section of the cornea showing subtle inflammation of the stroma with a focus of exudates posterior to Descemet membrane, suggestive of keratic precipitates (arrow) (hematoxylin-eosin, original magnification ×400). F, The exudates showing a single focus of microsporidia (arrow) (1% acid-fast stain, original magnification ×1000). G, Slitlamp picture showing clear corneal graft without any recurrence.
Das S, Sharma S, Sahu SK, Vemuganti GK. Intraocular Invasion by Microsporidial Spores in a Case of Stromal Keratitis. Arch Ophthalmol. 2011;129(4):512-526. doi:10.1001/archophthalmol.2011.61
Microbial keratitis is a visually disabling condition caused by a variety of infectious organisms. Although uncommon, microsporidial stromal keratitis has recently been reported as an emerging cause of stromal keratitis.1 Intraocular microsporidiosis causing endophthalmitis and sclerouveitis with clear cornea has been reported,2,3 although there was no evidence of contiguous anterior chamber involvement. We report a rare case of microsporidial stromal keratitis in which microsporidial spores were detected from corneal scraping, corneal tissue, and endothelial exudates.
A 40-year-old woman had intermittent pain, redness, photophobia, and decreased vision in her right eye for 1 year. She had trauma with a leaf 1 year before her initial visit to us. Since then, she had been treated irregularly with topical antiviral medication (acyclovir, 3%) by various health care providers.
On examination, her best-corrected visual acuity was 20/70 OD. Slitlamp biomicroscopic examination of the right eye revealed conjunctival congestion, central stromal edema with Descemet folds, and keratic precipitates (Figure, A). Her intraocular pressure was normal. Based on results of the clinical evaluation, a diagnosis of herpetic viral endotheliitis was made. She began treatment with systemic acyclovir, 400 mg 5 times daily, and topical corticosteroid (prednisolone acetate, 1%). Although her visual acuity and clinical picture improved, she revisited us 4.5 months after the initial visit with a decrease in vision, tearing, and pain that had lasted 15 days. She was using topical steroid once every other day. Her visual acuity was light perception with projection OD. There was a 3.8 × 2.7-mm central full-thickness stromal infiltrate. The endothelium showed exudates arranged as a sheet. The corneal scrapings examined in potassium hydroxide and calcofluor white mount (Figure, B) showed multiple oval microsporidial spores. The spores were also seen in Gram staining of the corneal scraping (Figure, C). She began intensive treatment with topical polyhexamethylene biguanide, 0.02%, eyedrops. Owing to progressive thinning and descemetocele formation (Figure, D), she underwent tissue adhesive application 4 days later. After a week with no response to medical therapy, she underwent therapeutic penetrating keratoplasty. Histopathologic examination of the corneal tissue showed multiple microsporidial spores within the stroma as well as in the subendothelial exudates with intact Descemet membrane (Figure, E and F). The postoperative period was uneventful. At the last follow-up, 6 months postoperatively, the graft was clear with visual acuity of 20/200 (Figure, G).
Stromal keratitis due to microsporidium is less common than superficial keratoconjunctivitis. It is frequently misdiagnosed as herpes simplex keratitis. Previous reports have described various clinical pictures of stromal keratitis such as stromal edema with anterior to mid and/or deep stromal involvement with or without endothelial exudates and corneal opacity.1 However, to our knowledge, there are no reports documenting microsporidial spores in the endothelial exudates. The finding of intact Descemet membrane in histopathologic examination suggests that microsporidial spores may indeed pass through Descemet membrane into the anterior chamber, similar to fungi. Recently, microsporidia have been phylogenetically shown to be fungi, and their tissue behavior akin to that of fungi would be expected.4
Our patient had clinical features of herpetic viral endotheliitis at the initial visit, which improved initially with antiviral treatment. There is a possibility that the patient may have had viral keratitis initially and then became secondarily infected with microsporidium. Also, coinfection by microsporidia with herpes cannot be excluded.
Penetrating graft rather than lamellar keratoplasty is recommended for patients with deep stromal involvement to avoid any chance of recurrence in the lamellar bed.5 In our case, the presence of microsporidial spores in the endothelial exudates highlights the possible penetration of microsporidial spores through intact Descemet membrane, thereby emphasizing the need for penetrating keratoplasty in cases of deep stromal involvement, especially with endothelial exudates.
We conclude that endothelial exudates may manifest in microsporidial keratitis, and the spores may be present in the endothelial exudates.
Correspondence: Dr Das, Cornea and Anterior Segment Service, LV Prasad Eye Institute, Patia, Bhubaneswar, Orissa 751024, India (email@example.com).
Financial Disclosure: None reported.
Funding/Support: This work was supported by the Hyderabad Eye Research Foundation.