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 microns 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 microns (mean -38 microns) and AOD500 by -151 to +157 microns (mean -42 microns); 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.