Intraocular Pressure (IOP) Elevation Reduces Schlemm’s Canal Cross-Sectional Area (SC-CSA) in Living Human Eyes

Abstract

 

Purpose

 

Previously, we demonstrated reduced 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) was imaged by spectral-domain optical coherence tomography (Cirrus HD-OCT, Carl Zeiss Meditec, USA) at baseline and with IOP elevation (ophthalmodynamometer set at 30 Grms force). IOP 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. SC-CSA at 5 locations within a 1 mm length of SC was measured in ImageJ as described previously (IOVS 2010; 51(8): 4054-4059). The effect of IOP elevation on SC-CSA was quantified by linear mixed-effects model.

 

Results

 

Mean IOP increase was 189% (Table). Mean SC-CSA was decreased 32% (p < 0.001; Figure, Table). The estimate (95% confidence interval) for SC-CSA response to IOP change was -66.6 (-80.6 to -52.7) μm²/mmHg.

 

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.

 

 

IOP and Schlemm’s canal cross-sectional area (SC-CSA) at baseline and elevated pressure. Mean (Standard deviation) are presented.

 

 

Numerous vascular landmarks (yellow arrows) were used to identify the same location for measurement at 2 pressures (top). Schlemm’s canal was visibly compressed at high IOP (bottom).

 

Keywords: 550 imaging/image analysis: clinical • 568 intraocular pressure