Evaluation of episcleral silicone matrix cyclosporine implants for presumed equine immune-mediated keratitis: a...

Immune-mediated keratitis (IMMK) is a chronic inflammatory corneal disease in horses. Long-term topical therapy with cyclosporine is often impractical, highlighting the need for sustained-release alternatives.

To assess clinical response, tolerability, and duration of effect of episcleral silicone matrix cyclosporine implants (ESMC) in horses with presumed IMMK.

Medical records of 12 horses (14 eyes) treated between 2019 and 2023 were retrospectively reviewed. IMMK subtypes were classified as epithelial (n = 3 eyes), anterior stromal (n = 9), or mid-stromal (n = 2). Collected data included treatment success or failure, complications, and duration of therapeutic effect. Statistics were applied with parametric and non-parametric testing.

No local or systemic adverse effects were observed. All epithelial IMMK eyes (3/3) achieved treatment success, with a median duration of therapeutic effect of 698 days (interquartile range - IQR 375). Seven of nine anterior stromal eyes presented successful outcome, with median duration of therapeutical effect of 104 days (IQR 88). Two eyes failed, requiring enucleation or surgical management. Both eyes with mid-stromal IMMK were classified as failure, with a median duration of therapeutic effect of 39 days (IQR 3). Significant differences in the duration of therapeutic effect were detected between epithelial and anterior stromal (p = 0.04) and between epithelial and mid-stromal subtypes (p = 0.03). No correlation was found between the number of implants and the duration of therapeutic effect (p = 0.7).

Episcleral silicone matrix cyclosporine implants were well tolerated in horses with presumed IMMK. The treatment showed high success rates in epithelial and anterior stromal subtypes, but poor outcomes in mid-stromal subtype. The therapeutic effect was longest in epithelial IMMK, suggesting implant efficacy may vary with disease subtype.