Table 1 displays the demographic characteristics and macular thicknesses of the study participants at each subfield. Average macular thickness was lowest at the fovea and highest at the inner superior subfield. Overall, macular thickness was higher at the inner subfields compared with the outer subfields.
Table 2 shows the estimated heritability of macular thickness at each subfield and the intraclass correlations of macular thickness within monozygotic twin pairs, parent–child pairs, and sibling pairs. The intraclass correlations of macular thickness within the monozygotic twin pairs were more than twice those of parent–child pairs and sibling pairs at most subfields, with the exceptions of the outer nasal and outer temporal areas. Age, sex, and axial length accounted for 2–20% of the variations in macular thickness.
Heritability of macular thickness at each subfield after adjusting for age, sex, and axial length were 0.76, 0.73, 0.70, 0.56, 0.67, 0.70, 0.73, 0.29, and 0.36 at the fovea, inner superior area, inner inferior area, inner nasal area, inner temporal area, outer superior area, outer inferior area, outer nasal area, and outer temporal area, respectively.