Long-term effect on the equine eye of an intravitreal device used for sustained release of cyclosporine A.

The study investigates the long-term effects of intravitreous cyclosporinee A (CsA) implantation in horses, specifically looking at potential toxicity. The procedure generally had no significant complications, but some instances of inflammation were recorded.

Study Methodology

• The researchers carefully selected ten adult horses with normal ophthalmic features to minimize possible external factors that could affect the study’s results.
• The procedure involved implanting a CsA device in one eye for four horses, while six horses had the right eye implanted with a CsA-containing device and the left eye with a device without the drug (serving as a control).
• The locations for implant were the vitreous of the eye through a sclerotomy, a purposeful cut or puncture, a centimeter posterior to the limbus in the dorso-temporal quadrant.
• The researchers performed Scotopic electroretinograms (ERGs) – tests to measure the effect of the implant on eye function – before the procedure and at regular intervals (1 week, 1 month, 3 months, 6 months, 9 months, and 12 months) after surgery.
• Depending on which interval they were at, some horses were euthanized to allow for a thorough examination of the eye structures and devices.

Findings

• Most of the implants (14 out of 16 eyes) were well-received by the horses’ bodies with little to no inflammation recorded after the procedure. In these cases, the eyes regained their normal appearance within a week.
• In two instances, severe inflammation occurred resulting in phthisis bulbi – a shrinking or atrophy of the eyeball – by 28 days. One of these instances was suspected to be bacterial endophthalmitis – an eye infection – and the other resulted from trauma to the lens during implantation.
• Regarding the ERGs, no significant changes were observed in the results from before the procedure, indicating that eye function remained stable.
• The CsA levels in the eye fluids and peripheral blood were found to be below the detection limit, suggesting limited if any systemic absorption of the drug.
• Most histologic findings showed only very minor cellular infiltrate, further supporting the low inflammation response to the implant.

Conclusions

• The CsA devices were generally well tolerated, with no long-term complications arising directly from the implants themselves.
• The only notable complications were due to inadvertent surgical trauma or contamination during the procedure, highlighting the importance of surgical carefulness when implanting these devices.
• Overall, the study suggests that the implantation of CsA devices could be a safe, long-term solution for the treatment of equine recurrent uveitis, a common eye disease in horses.