Ocular biomechanics and glaucoma

Abstract

Glaucoma is the leading cause of irreversible blindness worldwide. Ocular biomechanical properties have been implicated in glaucoma pathogenesis, but existing commercial devices cannot determine changes in specific tissues. We recently performed a study to compare corneal wave speed (a measure of corneal elasticity) and ocular rigidity (a whole eye measurement of ocular biomechanics) between glaucomatous and normal eyes. Twenty glaucomatous eyes from 10 patients and 20 normal eyes from 13 controls, matched for age, intraocular pressure (IOP), and axial length were included. Ocular rigidity was calculated based on the difference in supine IOP by pneumatonometry with and without a 10-g weight. Corneal wave speed was determined by ultrasound surface wave elastography in which a small, 0.1 s harmonic vibration at 100 Hz was generated through the closed eyelids. Wave propagation was captured by an ultrasound transducer, and wave speed was determined from the phase change with distance. No significant differences in corneal wave speed between glaucomatous and normal eyes were detected (P = 0.17). However, ocular rigidity was significantly lower in glaucomatous eyes (0.0218 ± 0.0033 vs 0.0252 ± 0.0050 μl−1, P = 0.01). While lower ocular rigidity is consistent with altered biomechanics in glaucoma, the lack of a difference in corneal wave speed suggests that corneal tissue may not be significantly affected, and scleral changes likely play a more important role.