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

Overview

• This study evaluated the safety, effectiveness, and duration of episcleral silicone matrix cyclosporine implants (ESMC) for treating immune-mediated keratitis (IMMK), a chronic corneal inflammation in horses.
• The researchers retrospectively analyzed treatment outcomes in 14 eyes from 12 horses with different IMMK subtypes to determine implant efficacy and tolerability.

Background

• Immune-Mediated Keratitis (IMMK): A chronic inflammatory condition affecting the cornea of horses.
• Current Treatment Challenges: Topical cyclosporine applied over the long term is often impractical in horses due to difficulties in administration and compliance.
• Need for Alternative: Sustained-release drug delivery systems may offer improved treatment adherence and consistent therapeutic levels.

Research Objective

• To assess the clinical response, safety parameters, and duration of therapeutic effect of episcleral silicone matrix cyclosporine implants in horses diagnosed with presumed IMMK.

Methodology

• Study Design: Retrospective analysis of medical records from 2019 to 2023.
• Sample: 12 horses contributing 14 affected eyes.
• IMMK Subtype Classification:
  • Epithelial IMMK: 3 eyes
  • Anterior stromal IMMK: 9 eyes
  • Mid-stromal IMMK: 2 eyes
• Parameters Recorded:
  • Success or failure of treatment
  • Any local or systemic complications
  • Duration of therapeutic effect post-implantation
• Statistical Analysis: Non-parametric testing was used to compare effectiveness across subtypes and correlate implant number with duration of effect.

Key Findings

• Safety: No local or systemic adverse effects were noted across all treated horses and eyes.
• Epithelial IMMK:
  • All 3 eyes showed treatment success (100% success rate).
  • Median duration of therapeutic effect was 698 days (approximately 1.9 years), with interquartile range (IQR) of 375 days.
• Anterior Stromal IMMK:
  • 7 out of 9 eyes were successfully treated (~78% success rate).
  • Median duration of effect was 104 days (around 3.5 months), IQR 88 days.
  • 2 eyes failed treatment, requiring more invasive interventions (enucleation or surgery).
• Mid-Stromal IMMK:
  • Both cases failed treatment (0% success rate).
  • Median therapeutic effect lasted 39 days (just over 1 month), IQR 3 days.
• Statistical Significance:
  • Difference in duration of therapeutic effect between epithelial and anterior stromal subtypes was statistically significant (p = 0.04).
  • Difference between epithelial and mid-stromal subtypes was also significant (p = 0.03).
  • No significant correlation was found between the number of implants placed and the length of therapeutic effect (p = 0.7).

Conclusions and Implications

• Effectiveness: Episcleral silicone matrix cyclosporine implants are a well-tolerated treatment option for horses with IMMK, especially effective in epithelial and anterior stromal subtypes.
• Subtype-Specific Response: The implant’s duration and success appear to depend on the IMMK subtype, with best results in epithelial IMMK and poor outcomes in mid-stromal IMMK cases.
• Clinical Relevance: This sustained-release implant offers a promising alternative to frequent topical cyclosporine, improving long-term management feasibility for equine patients.
• Future Directions: Additional prospective studies could optimize implant use, assess long-term effects, and explore alternative treatments for mid-stromal IMMK cases.