SummaryThe purpose of this study was to determine the efficacy and duration of effect of a subscleral cyclosporine A implant in horses with immune-mediated keratitis (IMMK). The study at hand describes the cases of fifteen horses with mature IMMK that were presented to the Tierklinik Hochmoor for further treatment. In theses horses, a cyclosporine A drug delivery device was placed subsclerally adjacent to the suprachoroidal space under general anesthesia. Follow-up was evaluated for up to 53 months duration after implant placement. Objective assessment showed an improvement in 66.7% of patients. Four of the patients suffered a recurrence of symptoms. This study yields promising results for the long-term treatment of IMMK in horses. Sport horses and patients suffering from frequently recurring episodes of IMMK could benefit greatly from this alternative treatment method.