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Variance of peripheral refraction in young twins

Purpose: Ocular aberrations in the fovea are more similar between Monozygotic (MZ) than Dizygotic (DZ) twins [Tabernero et al. Invest Ophthalmol Vis Sci. 2017 Apr 1;58(4):1964-1970]. This suggests a greater genetic influence on the foveal optics variance. Here, we extended the study to compare peripheral refractive error between MZ and DZ twins.

Methods: 41 MZ and 32 DZ couples of young university students (age range: 18 to 36 years) with normal vision were included in this study from the Murcia Twin Registry, Spain. We used an open-view peripheral Hartmann-Shack wave-front sensor (VPR, Voptica SL, Murcia, Spain) for measuring peripheral aberrations in the horizontal meridian (from 35° nasal up to 35° temporal retina). The relative peripheral spherical equivalent (SE) was obtained by subtracting each data point from the line of sight. A reference peripheral profile was obtained by averaging the data for each angle from the whole sample (OD; n=146 eyes). Then for each subject, the root mean square error (RMSE) was calculated as a metrics to describe the difference between the actual profile and the reference one.

Results: The foveal SE was -1.67±1.77 D (range: +2.60 to -5.50 D) for MZ and -2.47±2.00 D (range: +0.08 to -7.20 D) for DZ couples, with a similar intraclass correlation coefficient (ICC) for both twin groups (ICCMZ : 0.83; ICCDZ : 0.72). This suggests an environmental impact in this group of young university students. However, while comparing the peripheral metrics (RMSE), ICC was much higher for MZ twins (0.80) than DZ twins (0.15). On the other hand, there was no correlation (ICC = 0.04) between SE at the line of sight and the RMSE across all subjects.

Conclusions: Refractive error was similarly correlated for this set of MZ and DZ young university twin couples. But MZ siblings showed higher resemblance in peripheral refractive error than DZ couples. Higher similarity of the peripheral profiles among MZ couples could be explained by more comparable ocular optics and eye length.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 – May 2, 2019.

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