Long-term effects of Q-switched ruby laser on monkey anterior chamber angle

In an attempt to clarify whether pulsed lasers might be able to cause permanent fistulas from the anterior chamber to the interior of the canal of Schlemm, slightly suprathreshold, low energy, small diameter Q-switched ruby laser pulses were applied to the trabecular meshwork of nine eyes of six rhesus monkeys. Clinical examinations during the next 2 months disclosed no adverse effect on the cornea, iris, lens, or retina. There was transient mild inflammation in five eyes. Intraocular pressure was not changed significantly; the facility determined by perfusion of the anterior chambers at 2 months was normal. Light microscopy and scanning electron microscopy show localized trabecular lesions; some are slightly indented, but there is no persistent penetration to Schlemm's canal. Endothelial cells, confluent with those of the cornea, cover the inner (anterior chamber) surface of the lesions. Cross-sections through the center of a lesion show that trabecular meshwork and Schlemm's canal have been obliterated by the treatment and healing; these changes are similar to those previously seen after argon laser monkey trabecular treatment. In the untreated areas, between pulsed laser application sites, trabecular meshwork and Schlemm's canal are normal by light microscopic and scanning electron microscopic examination. Any effect on IOP from this particular type of pulsed laser treatment of the trabecular meshwork is probably not due to trabeculopuncture and flow of fluid through the fistula.