Rationale: Infectious keratopathy is an ocular emergency with the potential to cause irreversible blindness.Patient's concerns: A 63-year-old diabetic man presented with a 3-day history of painful red right eye. He had a history of multiple ocular surgeries in the affected eye without recent ocular trauma. Diagnosis: Infective crystalline keratopathy secondary to Citrobacter koseri. Interventions: Topical corticosteroids were discontinued, and dual topical antibiotic therapy of moxifloxacin 5％ and gentamycin 0.3％ were applied. Outcomes: Twelve hours after the start of treatment, the crystalline nature of the infiltrate disappeared, with enlargement of the epithelial defect. The antibiotic regime was continued and the lesion healed within a week of presentation with residual scarring. Lessons: Infective crystalline keratopathy classically presents with intrastromal branching fern-like opacities and minimal anterior segment inflammation in an immunosuppressed eye. The mainstay of management is corticosteroid discontinuation and the administration of empirical antibiotics until the results of the culture and sensitivity are available. In Citrobacter-related cases, treatment may result in a suppurative appearance before healing of the lesion.