Morphological changes and potential mechanisms of intraocular pressure reduction after micropulse transscleral cyclophotocoagulation in rabbits.

INTRODUCTION Micropulse transscleral cyclophotocoagulation (MP-TSCPC) is a method for intraocular pressure (IOP) reduction in patients with glaucoma; however, the specific mechanisms underlying its ability to reduce IOP remain unclear. We therefore investigated the morphological changes and mechanisms of intraocular pressure (IOP) reduction after MP-TSCPC. METHODS The right eyes of four pigmented rabbits were treated with MP-TSCPC with power setting corresponding to those used in glaucoma patients (1 power: 2,000 mW; time: 160 sec; duty cycle: 31.3%). Power settings of 1, 1/8, 1/16, and 1/32 power were applied to the right eyes. The left eyes were used as controls. A light microscope and electron microscope were used to observe morphological findings after 1 week of MP-TSCPC. IOP and IOP reduction rate were compared before and after MP-TSCPC application on days 1, 3, and 5, and at 1 week. RESULTS In the pre-MP-TSCPC, IOP was 16.7 ± 0.6 mmHg. The IOP of rabbit treated with the 1 power was 3 mmHg, with an IOP reduction rate of 80%; however, the eyes developed phthisis bulbi. The IOP was 7.0 ± 0.0 mmHg 1 week after MP-TSCPC (IOP reduction rate: 59%) in rabbit treated with the 1/8 power. Reduction in IOP was observed, but there was significant tissue invasion to the ciliary body. The IOP was 10.3 ± 0.6 mmHg (IOP reduction rate: 40%) 1 week after MP-TSCPC in rabbit treated with the 1/16 power, which was more effective to reduce IOP than that with the 1/8 power. Tissue invasion to the ciliary body was negligible, nonpigmented epithelial cells of the pars plicata were damaged, basal infoldings were destroyed, and repair was accompanied by proliferating tissue. No IOP reduction or tissue change was observed in rabbit treated with the 1/32 power. CONCLUSION A potential mechanism for IOP reduction in pigmented rabbits is aqueous humor transport dysfunction due to damage to the nonpigmented epithelial cells of the pars plicata and destruction of basal infoldings. The power of MP-TSCPC was consistent with both morphological changes and IOP reduction.