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Arthur J Sit, Arash Kazemi, Boran Zhou, Xiaoming Zhang; Comparison of Ocular Biomechanical Properties in Normal and Glaucomatous Eyes Using Ultrasound Surface Wave Elastography. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1218.
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© ARVO (1962-2015); The Authors (2016-present)
Biomechanical properties of the eye are important in understanding glaucoma. However, specific tissues that may be affected are unclear. In this study, we used a novel method to determine wave speed propagation (a measure of tissue elasticity) in the cornea of normal and glaucomatous eyes. We also determined the ocular rigidity coefficient (a global measure of ocular biomechanics) in the same eyes.
Twenty eyes of 10 glaucoma patients and 20 eyes of 10 normal controls, matched for age and IOP, were included. IOP was measured by using pneumatonometry. Ocular rigidity coefficient was calculated from IOP measured in the supine position with and without a 10-gm weight added to the tonometer. Central corneal thickness (CCT) was measured by using Scheimpflug imaging. Wave propagation speed in the cornea was measured by using surface wave elastography. With this technique, a spherical-tipped probe (4 mm diameter) was placed on the closed eyelid and vibrated at 100 Hz for 0.1 second (Figure). Tissue motion from surface waves was recorded by ultrasonography and wave speed was calculated using the phase gradient method. Measurements for normal and glaucoma eyes were compared by using generalized estimating equation models to account for possible correlation between fellow eyes of the same subject.
CoCorneal wave speed was similar between normal and glaucomatous eyes (P=0.4; Table). However, ocular rigidity was significantly lower in glaucomatous eyes (P<0.001) compared with normal eyes. There was no difference in age, IOP, or CCT between the two groups (P>0.3). In our cohort, glaucoma patients had a higher axial length than normal controls (P<0.001).
The lack of difference in corneal wave speed between normal and glaucomatous eyes suggests that any abnormalities in ocular biomechanical properties in glaucoma do not significantly affect corneal tissue. The lower ocular rigidity in glaucomatous eyes suggests that a more compliant ocular shell may predispose to glaucoma. Axial length may be a confounding factor in this cohort of subjects. Future work will need to compare wave speed in sclera between normal and glaucomatous eyes.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
Figure: (A) Selection of corneal points on ultrasound image; (B) Calculation of wave speed based on phase change at each point.
Table: Comparison of Biomechanical Properties for Normal and Glaucoma Eyes
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