Barrio-Barrio and associates, using spectral-domain optical coherence tomography (SD OCT) thickness data from their study of prepubertal children, report that male subjects are more likely than female subjects to have thicker retinas, leading them to conclude that genetic and not sex-hormonal differences may explain our finding of thicker retinas on SD OCT in older male compared to female adults. The notion of genetic factors explaining thicker central retina as determined by OCT is supported by a heritability estimate of 0.90 in a study using monozygotic and dizygotic female twin pairs. A different study of macular thickness found thicker retinas in younger persons, which led the authors to suggest that the differences between the sexes were due, in part, to gonadal hormone levels. The role of genes and environmental factors that determine retinal thickness remain to be further elucidated.