Biphasic intraocular pressure response to laser irradiation of the iris in rabbits

The possibility of an acute increase in intraocular pressure (IOP) following laser iridotomy is well known. However, little attention has been paid to the hypotony after laser irradiation of the iris. We performed this study to evaluate the effect of laser irradiation of the iris on the IOP in pigmented rabbits. IOP, aqueous flare values, and aqueous prostaglandin E₂ levels were measured before and 1,4, 12, and 24 h after argon laser treatment. The IOP showed a prolonged reduction for 24 h following an initial transient increase. Flare values and aqueous prostaglandin E₂ levels reached a peak 1 h after laser treatment, followed by a progressive reduction. Argon laser peripheral iridoplasty that can separate the iris from the trabecular meshwork by the mechanical force resulting from a contraction burn is used sometimes in treating angle-closure glaucoma. Our results showed that the laser irradiation of the iris itself can cause ocular hypotony, so that this phenomenon may be another explanation of the IOP response after peripheral iridoplasty.