Ultrasound biomicroscopic analysis of the effect of pilocarpine on the anterior chamber angle

Background: This study was carried out to determine the effects of pilocarpine on the anterior chamber angle in healthy volunteers. Methods: We measured changes in anterior chamber depth (ACD), trabecular-iris angle (TIA), angle opening distance at 250 and 500 mu m from the scleral spur (AOD250 and AOD500), and iris thickness using ultrasound biomicroscopy in 48 eyes of 48 normal volunteers (ages 18-57 years, mean 34.8 years) before and 1 h after instillation of 2% pilocarpine. Results: Pilocarpine altered the TIA by -18.6 degrees to +10.5 degrees (mean -4.16 degrees), and change in the TIA increased significantly and linearly in relation with decrease in the pretreatment TIA (r = 0.929). Pilocarpine altered AOD250 change by -136 to +94 mu m (mean -38 mu m) and AOD500 by -151 to +157 mu m (mean -42 mu m); changes in the AOD250 and AOD500 were significantly correlated to the pretreatment AOD250 and AOD500 values, respectively (r = 0.923 and r = 0.896, respectively). The pilocarpine-induced change in the ACD showed a linear relationship to the pretreatment ACD (r = 0.887). The changes in the TIA, AOD250 and AOD500 showed greater increases in association with lower pretreatment ACD (r = 0.848, r = 0.891, r = 0.842) and smaller change in the ACD (r = 0.834, r = 0.839, r = 0.812). Conclusions: The response of the anterior chamber angle to pilocarpine narrowing Or widening, depended on its pretreatment state. The ability to predict the pilocarpine-induced change in the angle before the instillation of pilocarpine would be helpful in treating patients with glaucoma.