BACKGROUND/AIMS: Keratitis, especially when long-standing and unresponsive to common antimicrobial treatment, leads to a suspicion of fungal aetiology. METHODS: Photographically documented case report. RESULTS: A 65-year-old man with diabetes was referred for corneal abscess unresponsive to antibiotic and antifungal treatment lasting 6 weeks. Corneal biopsy was performed following a 72-hour washout for identification of bacteria and fungi. Previously administered drops were withdrawn and only preservative-free artificial tears were maintained. Neither bacteria nor fungi were cultured. After 2 weeks, the clinical situation had conspicuously improved. CONCLUSION: Over-treatment of corneal affections fearing mycosis may lead to toxic keratopathy.