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. 2014 Mar 25;55(3):1805-9.
doi: 10.1167/iovs.13-13264.

IOP elevation reduces Schlemm's canal cross-sectional area

Larry Kagemann  1 , Bo Wang, Gadi Wollstein, Hiroshi Ishikawa, Jessica E Nevins, Zach Nadler, Ian A Sigal, Richard A Bilonick, Joel S Schuman
Affiliations

IOP elevation reduces Schlemm's canal cross-sectional area

Larry Kagemann et al. Invest Ophthalmol Vis Sci. .

Abstract

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.

Keywords: ophthalmodynamometer; optical coherence tomography; outflow tract imaging.

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Figures

Figure 1
Figure 1
Radial optical coherence tomography images of the limbus (upper left) include a portion of the anterior chamber and iris (lower right), as well as the peripheral cornea and sclera.
Figure 2
Figure 2
B-scans of Schlemm's canal (top) at baseline (top left) and during acute IOP elevation (top right) matched based upon vascular landmarks (yellow arrows). Magnification reveals a decrease in Schlemm's canal cross-sectional area from baseline (bottom left) to high IOP (bottom right). Scale bars: 500 μm (scans have an anisotropic aspect ratio, and for that reason the horizontal and vertical scale bars are of different lengths).
Figure 3
Figure 3
Box plot showing the distribution of SC-CSAs at baseline and during acute IOP elevation.
Figure 4
Figure 4
Box plot showing the distribution of scan-to-scan SC-CSA difference at baseline and during acute IOP elevation.
See this image and copyright information in PMC

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