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Francis Carbonaro, Samantha Fahy, Margarida C. Lopes, Piro G. Hysi, Tim D. Spector, Christopher J. Hammond; Relationships Between Corneal Hysteresis And Ocular And Non-ocular Parameters In An Unselected Twin Cohort. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6262.
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Corneal hysteresis is a measure of the viscoelasticity of the cornea. Lack of scleral elasticity may be associated with glaucoma, and corneal hysteresis has been associated with progression of glaucoma. The purposes of this study was to measure corneal hysteresis in a large population-representative sample, to determine causes of variation in the normal population and associations with ocular and non-ocular parameters in particular weight and age.
2532 unselected individuals (mean age: 57.9 years, SD:10.3 years, range 19 -83 years) from 1266 twin pairs from the TwinsUK Adult Twin Registry were examined. Corneal hysteresis, intraocular pressure (IOP), and central corneal thickness (CCT) measurements were obtained with the Ocular Response Analyser (Reichert®, Buffalo, USA). Weight and height, together with blood pressure (BP), were assessed using standardised methodology. Spherical equivalent was calculated from autorefraction data. Data handling and preliminary analysis were undertaken using STATA
Data from 2501 right eyes were available for analysis. The mean corneal hysteresis was 10.3mmHg (SD 1.4mmHg). Corneal hysteresis was found to be significantly negatively correlated with age (r=-0.21, P<0.0005) and systolic BP(r=-0.08, P<0.05) and positively correlated with CCT (r=0.42, P<0.0005). There was no significant correlation found between corneal hysteresis and BMI (r=-0.02,P=0.52). When analysed individually, weight (r=-0.02, P=0.47) and height (r=-0.03, P=0.41) separately were still not related to corneal hysteresis. There was also no significant correlation between corneal hysteresis and IOP (r=0.04, P=0.33), Diastolic BP (r=-.004, P=0.24), or spherical equivalent (r=0.03, P=0.46). Results were unchanged if one of each pair of twins was selected randomly for inclusion.
In this large sample of a population-representative healthy population, corneal hysteresis appears to reduce with age and there was a small negative correlation with systolic BP, but not diastolic BP. Hysteresis does not appear to be associated with refractive error, or height or weight. As it is well known that glaucoma risk increases with age; could this study point to a hypothesis that reduced elasticity of the eye is in part responsible for increased susceptibility to optic nerve damage? Longitudinal data would be of interest to further understand the relationship between corneal hysteresis and these various parameters.
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