Abstract
To investigate the relationships between (i) thickness of the retinal nerve fiber layer, optic nerve head topography, and visual field parameters and (ii) corneal biomechanical properties in normal controls and patients with ocular hypertension and primary open-angle glaucoma. This observational, cross-sectional study included 68 eyes with primary open-angle glaucoma, 99 eyes with ocular hypertension and 133 control eyes. Corneal biomechanical properties, optic nerve head topographic features, retinal nerve fiber layer thickness, and visual fields were assessed in all cases. Corneal biomechanical properties, retinal nerve fiber layer thicknesses, and optic nerve head topographic features were compared among the groups. The associations between structural and functional measures of glaucomatous damage and corneal biomechanical factors were also evaluated. Significantly lower corneal hysteresis and corneal resistance factor values were observed in the primary open-angle glaucoma and ocular hypertension groups as compared with the control group, but there were no significant differences between the primary open-angle glaucoma and ocular hypertension groups. In the ocular hypertension group, no associations were observed between the corneal hysteresis and corneal resistance factor with values and the structural and functional parameters. In the primary open-angle glaucoma group, positive correlations were observed between the corneal hysteresis values and the global retinal nerve fiber layer thickness (p<0.01, r=0.27), mean retinal nerve fiber layer thickness (p<0.01, r=0.33), and mean deviation (p<0.01, r=0.26), and negative correlations were observed between the corneal resistance factor values, and the cup area (p<0.01, r=-0.39), cup-to-disk ratio (p=0.02, r=-0.28), linear cup-to-disk ratio (p=0.02, r=-0.28), and cup shape (p=0.03, r=-0.26). In the control group, weak correlations were detected between the corneal hysteresis and the cup area (p=0.03, r=0.19), cup-to-disk ratio (p=0.01, r=0.21), and linear cup-to-disk ratio (p=0.01, r=0.22). Distinct correlations were identified between the corneal hysteresis and corneal resistance factor values and the functional and structural parameters in the primary open-angle glaucoma and control groups. Corneal hysteresis and corneal resistance factor may have different roles in the pathophysiology of glaucoma.
Highlights
An ocular response analyzer (ORA) is a bidirectional applanation device that is less affected by corneal structure than other devices when estimating corneal biomechanical properties and evaluating intraocular pressure (IOP)(1)
Significantly lower corneal hysteresis and corneal resistance factor values were observed in the primary open-angle glaucoma and ocular hypertension groups as compared with the control group, but there were no significant differences between the primary open-angle glaucoma and ocular hypertension groups
By crude analysis without adjusting for central corneal thickness (CCT), age, IOP, axial length, or the presence of diabetes mellitus (DM), the corneal hysteresis (CH) and corneal resistance factor (CRF) values were higher in the ocular hypertension (OHT) and control groups than in the primary open-angle glaucoma (POAG) group, and there were no significant differences between the OHT and control groups
Summary
An ocular response analyzer (ORA) is a bidirectional applanation device that is less affected by corneal structure than other devices when estimating corneal biomechanical properties and evaluating intraocular pressure (IOP)(1). With the introduction of ORA, in vivo measurements of corneal biomechanical properties, including corneal hysteresis (CH) and the corneal resistance factor (CRF), have become possible for the first time[2]. CRF is a measure of the total viscoelastic resistance of the cornea to deformation[1]. Sclera, and lamina cribrosa are contiguous structures, the probable similarities in the biomechanical behaviors of these structures are the main factor supporting this association. Studies have reported higher CH values in patients with ocular hypertension (OHT) than in those with glaucoma[16,17,18,19]
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