The long‐term effects of semiconductor diode laser transscleral cyclophotocoagulation on the normal equine eye and intraocular pressurea

Abstract

To describe the long-term histologic and intraocular pressure (IOP) lowering effects of diode laser transscleral cyclophotocoagulation (TSCP) on the normal equine eye. Eight normal adult horses. TSCP was performed in one randomly assigned eye. Sixty spots were treated at settings of 1500 ms and 1500 mW. Two horses were randomly selected for euthanasia at 2, 4, 12, or 24 weeks post-TSCP. Both eyes were enucleated and histologically evaluated. Intraocular pressure was measured by applanation tonometry prior to TSCP, immediately post-TSCP, twice daily for 7 days post-TSCP and then monthly until study conclusion. A longitudinal model estimated the average IOP values for the treated and untreated eyes at 1 week, 1, 3, and 6 months post-TSCP. All treated eyes at all time periods exhibited four characteristic histologic lesions: scleral collagen hyalinization, ciliary body pigment dispersion and clumping, focal disruption of the ciliary body epithelium, and focal ciliary process atrophy. After TSCP, there were no significant changes in IOP from baseline for the control eyes, while the IOP in treated eyes was significantly decreased from baseline (P < 0.05) at all time periods. The estimated decrease in IOP in the treated eyes compared to baseline IOP at 6 months was -3.76 mmHg for an average decrease in IOP of 20% from baseline. Diode laser TSCP produces histologic lesions in the equine ciliary body that result in a significant and sustained decrease in IOP. TSCP may be an effective management for equine glaucoma.