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Arash Kazemi, Jay W McLaren, Christopher M Pruet, Shuai-Chun Lin, Xiaoming Zhang, Arthur J Sit; The Relationships between Corneal Elasticity Measured by Surface Wave Elastography and other Ocular Variables. Invest. Ophthalmol. Vis. Sci. 2016;57(12):3552.
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© ARVO (1962-2015); The Authors (2016-present)
Biomechanical properties of the eye are important for understanding the risk of glaucoma. The relationships between corneal elasticity and other ocular variables are unknown. In this study we determined Young’s modulus of elasticity in corneas of normal subjects by using a novel non-invasive technique based on surface wave elastography and determined relationships between corneal elasticity and corneal hysteresis (CH), corneal resistance factor (CRF), the ocular rigidity coefficient, and other ocular parameters.
In 28 eyes of 14 healthy participants (ages 25-63; mean 34.3 years) intraocular pressure (IOP) was measured by using Goldmann applanation tonometry (GAT) and pneumatonometry. The 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 from Scheimpflug images (Pentacam HR, Oculus). CH and CRF were measured by using the Ocular Response Analyzer (ORA, Reichert).The elasticity of the cornea was then determined by surface wave elastography. A spherical-tipped probe (4 mm diameter) was placed on the closed eyelid and vibrated at 100 Hz for 0.1 second. Surface waves were recorded by ultrasonography as they propagated around the eye and Young’s modulus was calculated from the measured speed of wave propagation. Associations between variables were explored by Pearson correlation and significances were determined by using generalized estimating equation models to account for possible correlation between fellow eyes of the same subject.
Young’s modulus of elasticity was strongly correlated with IOP (r=0.65, p<0.001 from GAT, and r=0.58, p<0.001 from pneumatonometry) but not with CRF (r=0.44, p=0.18), CH (r=0.25, p=0.57), or the ocular rigidity coefficient (r=-0.05, p=0.69).
Young’s modulus of elasticity in normal eyes increases as IOP increases, consistent with published in-vitro studies. The lack of correlations of CRF and the ocular rigidity coefficient with Young’s modulus suggest that these variables may not be surrogate measures of corneal elasticity. Further work is required to determine if elasticity is altered in glaucoma patients.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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