Q-switched neodymium-YAG laser trabeculopuncture in monkeys
S. Melamed, J. Pei, C. A. Puliafito and D. L. Epstein
In nine cynomolgus monkeys, trabeculopuncture was performed with a
Q-switched neodymium-YAG laser, using a pulse energy of 5 to 7 millijoules
and an exposure time of 14 nanoseconds. A penetration into Schlemm's canal
was successfully achieved with two to four pulses; this penetration was
accompanied by intraocular pressure (IOP) reduction and blood reflux into
the anterior chamber. However, after eight days, IOP returned to baseline
level, while white tissue was observed gonioscopically to fill in the
puncture sites. Histologically, one hour after laser treatment, a blasting
effect on the trabecular meshwork was observed with no signs of necrosis.
Ater eight days, a hypertrophic scar formed, with the corneal endothelium
extending over the scarred surface. At eight weeks and at six months after
laser treatment, further shrinkage of the scar and the formation of a
membrane over it was evident. Attempts to control scar formation by
preventing blood reflux or injecting fluorouracil subconjunctivally for two
weeks were unsuccessful. Scar formation at the trabecular puncture site
severely limits the applicability of this potentially simple glaucoma
treatment.
