Methods: Optical aberrations were measured in 116 eyes corresponding to 58 twins; 27 monozygotic (MZ) and 31 dyzogotic (DZ) pairs (age 54 years, SD 6 years). Corneal aberrations were estimated from the elevation data measured with a corneal topographer and using our own developed ray-tracing procedure to express aberrations in Zernike coefficients. Ocular aberrations were measured using a Hartmann-Shack sensort (AOnEye; Voptica SL, Murcia, Spain). Both procedures used the center of the pupil as a reference so that internal aberrations could be estimated by subtraction of corneal to ocular Zernike coefficients. Intraclass Correlation Coefficients (ICC) were used to estimate how strongly aberrations of twins resemble each other and genetic models were fitted to quantify heritability in the selected phenotypes.
Results: Spherical Aberration (SA) presented the highest value of the ICC in MZ twins (0.71 right eyes; 0.74 left eyes) while for DZ twins correlations were much lower (0.09 right eyes; 0.15 left eyes). The strong difference between MZ and DZ twins suggested a dominant genetic contribution to the variance of the SA. Corneal SA was also highly correlated in MZ twins (0.64 right eyes; 0.71 left eyes) compared to DZ twins (0.03 right eyes; 0.34 left eyes) and nearly at the same level as the crystalline (internal) SA (0.66 and 0.65 for right and left MZ; 0.14 and 0.41 for right and left DZ). In general, other higher order aberrations presented lower correlations than those of SA for both groups of twins but still the ICC of ocular higher order RMS in MZ twins were systematically higher than in DZ (0.36 and 0.40 for right and left MZ; 0.01 and 0.30 for right and left DZ). Model fitting results yielded heritability estimations for SA ranging between .5 and .7.
Conclusions: Variability in the optical aberrations of the components of the eye is far from being randomly generated. Heritability plays an important role to explain a large part of this variance. This is specially the case for SA, while for other aberration terms there was an increase in the contribution of unique random errors and relatively less genetic influence. Whether this genetic basis of the eye’s aberrations is linked or independent to refractive diseases should be subject of further research.