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).