Nd:YAG Laser Posterior Capsulotomy Does Not Produce Elevation of Intraocular Pressure in Cynomolgus Monkeys

Abstract

The mechanism of the intraocular pressure (IOP) elevation commonly seen in patients following neodymium (Nd):YAG laser posterior capsulotomy is unclear. Substance P, a potent polypeptide that is released into the eye after trigeminal nerve stimulation, may be the cause. In rabbits, topical application of nitrogen mustard causes a rise in IOP which is blocked by capsaicin, a presumed substance P depletor. In the present study, six eyes of three cynomolgus monkeys underwent extracapsular lensectomies. After 2 to 3 months, capsaicin was administered by retrobulbar injection on one side of each animal, and vehicle on the contralateral side. One day later, Nd:YAG laser posterior capsulotomies were performed using 31 mJ (total energy) per eye. Diurnal IOP measurements were made before and after the retrobulbar injections and the capsulotomies. Ten weeks later, laser capsulotomies were repeated using 200 mJ/eye without pretreatment with any potential blockers. None of the six eyes, each undergoing two separate capsulotomies 10 weeks apart, showed a postoperative rise in IOP. These results demonstrate that the cynomolgus monkey is a poor model for studying IOP elevation that often occurs following Nd:YAG laser posterior capsulotomy.