Genetic and environmental effects on oculometric traits.

Twenty twin pairs (9 monozygotic and 11 dizygotic) were examined to test the effect of genetic and environmental factors on the etiology of refractive error, axial length of the eyeball, and total astigmatism. The twins pairs were ascertained from the nationwide Finnish Twin Cohort Study (FTCS). The monozygosity was confirmed for nine pairs by a blood group analysis adopted for paternity testing procedures. The mean ages of the monozygotic twin pairs was 69 years and of the dizygotic twin pairs 63 years. Spherical equivalent of refractive error and axial length of the eyeball showed higher intrapair correlations among monozygotic pairs than among dizygotic pairs. This suggests, at least in part, a genetic etiology of these traits. Total astigmatism measured by retinoscopy did not show a significant difference in intrapair correlations between monozygotic and dizygotic twin pairs.