The heritability of corneal hysteresis and ocular pulse amplitude - A twin study

Purpose: To examine the roles of genetic and environmental factors in corneal hysteresis and ocular pulse amplitude by performing a classic twin study. Design: Cross-sectional twin study. Participants and/or Controls: Two hundred sixty-four twin pairs: 135 monozygotic (MZ) and 129 dizygotic (DZ). Methods: Corneal hysteresis was measured using the Reichert Ocular Response Analyzer (ORA; Reichert, Buffalo, NY), and ocular pulse amplitude was measured using the Pascal Dynamic Contour Tonometer (DCT; Swiss Microtechnology AG, Port, Switzerland). Main Outcome Measures: Contribution of genetic and environmental effects on corneal hysteresis and OPA among MZ and DZ twins. Results: The mean corneal hysteresis was of 10.24 +/- 1.54 mmHg and the mean ocular pulse amplitude was 2.88 +/- 0.97 mmHg. The MZ correlations were higher than DZ for both corneal hysteresis and ocular pulse amplitude (correlation coefficients, 0.75:0.42 and 0.59:0.32 for MZ:DZ twins, respectively). Modeling suggested heritability of corneal hysteresis of 0.77 (95% confidence interval [CI], 0.70-0.82), with the remaining proportion of variance because of individual environmental effects of 0.23 (95% CI, 0.18-0.30). For ocular pulse amplitude, the heritability was 0.62 (95% CI, 0.51-0.70), with the remaining proportion of variance the result of individual environmental effects of 0.38 (95% CI, 0.30-0.49). Conclusions: This study demonstrated that additive genetic influences explained most of the individual differences in corneal hysteresis and ocular pulse amplitude among these twins.