IOP elevation reduces Schlemm's canal cross-sectional area.

PURPOSE Previously, we demonstrated reduced Schlemm's canal cross-sectional area (SC-CSA) with increased perfusion pressure in a cadaveric flow model. The purpose of the present study was to determine the effect of acute IOP elevation on SC-CSA in living human eyes. METHODS The temporal limbus of 27 eyes of 14 healthy subjects (10 male, 4 female, age 36 ± 13 years) was imaged by spectral-domain optical coherence tomography at baseline and with IOP elevation (ophthalmodynamometer set at 30-g force). Intraocular pressure was measured at baseline and with IOP elevation by Goldmann applanation tonometry. Vascular landmarks were used to identify corresponding locations in baseline and IOP elevation scan volumes. Schlemm's canal CSA at five locations within a 1-mm length of SC was measured in ImageJ as described previously. A linear mixed-effects model quantified the effect of IOP elevation on SC-CSA. RESULTS The mean IOP increase was 189%, and the mean SC-CSA decrease was 32% (P < 0.001). The estimate (95% confidence interval) for SC-CSA response to IOP change was -66.6 (-80.6 to -52.7) μm(2)/mm Hg. CONCLUSIONS Acute IOP elevation significantly reduces SC-CSA in healthy eyes. Acute dynamic response to IOP elevation may be a useful future characterization of ocular health in the management of glaucoma.