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Harry A Quigley, Thao D Nguyen, Sahar Bedrood, Dan Midgett; Biomechanical Responses of Sclera and Lamina Cribrosa to IOP Change Assessed by Optical Coherence Tomography in Glaucoma Eyes. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3156.
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© ARVO (1962-2015); The Authors (2016-present)
To measure change in scleral curvature and anterior lamina cribrosa depth (ALD) globally and regionally in glaucoma eyes at different IOPs
Glaucoma eyes undergoing procedures to lower IOP were imaged by optical coherence tomography (OCT) and the position and curvature of the inner sclera and the ALD were compared at the different IOP levels in 34 eyes. OCT imaging was performed in a 6 mm square area centered on the fovea with 19 horizontal scans and at the optic nerve head with 6 radial scans. Models of scleral curvature and ALD were generated from manually marked positions on each scan image and compared to IOP level, stage of glaucoma damage in optic disc, nerve fiber layer and visual field both overall and by regional quadrant and clock hour.
Choroidal thickness significantly increased with IOP lowering (p = 0.002). Change in scleral curvature per mm Hg IOP decrease was more convex toward the cornea, but the mean change was not statistically significant (p = 0.48). Mean ALD was significantly deeper with larger cup/disc ratio, thinner rim area, and larger cup volume (p = 0.005, 0.006, and <0.0001), with thinner central corneal thickness, in men, and in non-white persons (p = 0.02, 0.02, 0.05, respectively). Mean change in ALD was either posteriorly and anteriorly, with overall mean = 27 + 142 µm (p = 0.3). Change in ALD was related to the lower IOP level of paired comparisons (p=0.006), but not to the IOP difference between image sessions (p=0.94). Eyes with no change in ALD had somewhat worse visual field damage than those with significant anterior ALD change (p=0.07). Regions within each optic nerve head corresponding to zones with thicker nerve fiber layer had greater ALD deepening (p = 0.0007).
The lamina moves either anteriorly or posteriorly with IOP increase, with greater displacement at lower levels of IOP. Glaucoma eyes and regions within glaucoma eyes associated with greater glaucoma damage exhibited stiffer responses. ALD change should be studied prospectively as a biomarker for glaucoma susceptibility.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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