A 49-year-old white man was seen in August 2009 with foreign-body sensation, blurred vision, and redness of his right eye for 2 weeks. Medical history was significant for metastatic thyroid cancer. His chemotherapy was discontinued because of neutropenia 1 month earlier and his white blood cell count had subsequently normalized. His best-corrected visual acuity (BCVA) was 20/25 OD and 20/15 OS. Right eye slitlamp examination demonstrated 20 to 25 raised epithelial opacities diffusely throughout the cornea with subepithelial infiltrates (Figure 1A). Follicles were present on the palpebral conjunctiva. Examination was otherwise normal in the right eye. Slitlamp examination of the left eye was normal. The clinical diagnosis was viral conjunctivitis, and treatment was started with topical prednisolone acetate, 1%, 3 times daily. At 1 week, the epithelial opacities and subepithelial infiltrates were improved, so corticosteroid use was tapered and discontinued. Three weeks later, the symptoms and signs returned, and BCVA worsened to 20/30 OD. Microsporidial keratitis was suspected based on clinical appearance and time course. Microscopic examination of a diagnostic epithelial scraping revealed aggregates of intracellular organisms in the cytoplasm of epithelial cells consistent with microsporidia (Figure 2A). Steroid use was discontinued, and treatment was begun with topical voriconazole, 1%, every 2 hours. After 8 days, BCVA was 20/25 OD with improved symptoms and signs. Voriconazole use was tapered over 4 weeks. The patient had resolution of symptoms and signs at his visit after the taper. Final BCVA was 20/15 OD.