Heritability of spherical equivalent: a population-based twin study among 63- to 76-year-old female twins.

PURPOSE: To examine the heritability of spherical equivalent (SE) in older women.

DESIGN

Population-based twin study.

PARTICIPANTS

Ninety monozygotic (MZ) and 86 dizygotic (DZ) female twin pairs aged 63 to 76 years who were born from 1924 through 1937.

METHODS

Ocular refraction was measured using an autorefractor and controlled by the subjective method. The contributions of genetic and environmental factors to individual differences in SE were estimated by applying an independent pathway model to twin data.

MAIN OUTCOME MEASURES: Contribution of genetic and environmental effects to the variation in SE.

RESULTS

Mean SE of the study population was 1.68 (standard deviation, ± 1.82) with no differences observed either between the MZ and the DZ individuals or between the left and the right eyes. The pairwise correlations were higher in the MZ sisters (intraclass correlation coefficient [ICC], 0.803 right eye and 0.807 left eye) than DZ sisters (ICC, 0.406 right eye and 0.435 left eye). Quantitative genetic modelling showed that 83% (95% confidence interval, 77%-87%) of the variance in SE could be explained by heritable factors.

CONCLUSIONS

Additive genetic influences explained most of the individual differences in SE among older Finnish women.