Analysis wave speed of optic nerve and optic nerve head for assessing normal tension glaucoma by using vibro-elastography technique

Background: This research aims to evaluate wave speed and viscoelasticity of ocular tissues including the optic nerve and optic nerve head of human eyes between normal tension glaucoma patients and healthy controls by using vibro-elastography techniques. Methods: Participants included 12 patients and 12 controls. Wave speed was measured at the optic nerve and optic nerve head in each subject and viscoelasticity was estimated by using Voigt model. Wave speed and viscoelasticity of the optic nerve and optic nerve head were compared between patients and controls by linear mixed models via a restricted maximum likelihood method. The correlation between intraocular pressure and wave speed, elasticity, and viscosity of patients was performed using the Pearson correlation coefficient. Findings: Significant differences in wave speed (p < 0.0005), elasticity (p = 0.0001) and viscosity p < 0.0001) between patients and controls at the optic nerve head. There was a moderate negative correlation (r = -0.50, p < 0.05) between wave speed and elasticity and intraocular pressure at the optic nerve of patients but no correlation (p > 0.05) between wave speed, elasticity, and viscosity and intraocular pressure at the optic nerve head of patients. No significant difference and correlation among wave speed, elasticity, and viscosity vs. intraocular pressure of the control group at the optic nerve and optic nerve head. Interpretation: Ultrasound vibro-elastography is useful for noninvasive measurement of viscoelasticity of ocular structures. The glaucoma patient is associated with biomechanical property changes in the optic nerve and optic nerve head, suggesting another way to assess glaucoma focusing on the optic nerve and optic nerve head.