Laser peripheral iridoplasty (LPI) is widely used in the treatment of glaucoma by flattening the iris and widening angle of anterior chamber (AA). However, no evidence suggests the optimal site of LPI in iris.

This study was to compare the therapeutic effects of LPI at different sites of iris for glaucoma.

Glaucoma models were established in the right eyes of 40 healthy adult male pigment rabbits by intrachamber injection of 0.1 ml compound carbomer solution with 0.3% carbomer and 0.025% dexamethasone.The models were randomly divided into model control group, corneoscleral limbus group, one spot from corneoscleral limbus group and two spots from corneoscleral limbus group.LPI was performed at corresponding site of iris by 532 nm argon laser with the spot diameter 500 μm, energy 300 mW, exposure time 0.3 seconds and laser number 24 spots, and the rabbits in the model control group did not receive LPI.Intraocular pressure (IOP), coefficient of outflow facility (C value) were measured and calculated with Schiötz tonometer before LPI and 2, 4, 7, 14 and 30 days after LPI, and anterior chamber depth (ACD), AA, anterior chamber angle opening distance within 500 μm radius from scleral spur (AOD500) were measured with ultrasound biomicroscope (UBM). The eyeballs were extracted 30 days after LPI, and the chamber angle were observed under the optical microscope after hematoxylin and eosin staining.The use and care of the animals complied with the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health.

UBM showed that compared with the model control group, the anterior chamber angle was evidently widened in all the LPI groups, with the best effectiveness in the one spot from corneoscleral limbus group and the worst one in the two spots from corneoscleral limbus group.Compared with the model control group, the IOP was evidently reduced, and C values, AA and AOD500 were significantly increased in the corneoscleral limbus group, one spot from corneoscleral limbus group and two spots from corneoscleral limbus group after LPI, showing significant differences among the four groups (IOP: F_group=16.848, P<0.01; C value: F_group=9.629, P<0.01; AA: F_group=62.336, P<0.01; AOD500: F_group=77.779, P<0.01). IOP was reduced and C value, AA and AOD500 were increased in 2, 4, 7, 14 and 30 days after LPI as compared with before LPI, with significant differences over time (IOP: F_time=3.041, P=0.011; C value: F_time=4.311, P<0.01; AA: F_time=14.627, P<0.01; AOD500: F_time=20.378, P<0.01). Compared with the model control group, the ACD was significantly increased in the corneoscleral limbus group and one spot from corneoscleral limbus group, and that in the two spots from corneoscleral limbus group was significantly reduced, and the ACD was insignificantly increased over time after LPI (F_group=18.017, P<0.01; F_time=0.022, P=1.000). Hematoxylin and eosin staining showed that the trabecular meshwork and adhesion of tissure were reopened and the anterior chamber angle was widened after LPI.

LPI can widen anterior chamber angle and lower the IOP.The best therapeutic outcome for glaucoma is displayed when LPI is performed at the iris site corresponding to one spot from the corneoscleral limbus.

Glaucoma/surgery; Iris/surgery; Laser therapy; Intraocular pressure; Anterior chamber angle; Treatment outcome; Laser peripheral iridoplasty; Rabbits, pigment