Purpose : Appropriate dimensions and geometry (angles) of the eye are required to form high quality retinal images. We evaluated the relative contribution of genetic and environmental factors to the variance of the thickness of ocular structures and angle kappa.
Methods : A group of 46 twins were included in the study: 21 monozygotic (MZ) pairs (age: 54.1 years, SD=7.4) and 25 dizygotic (DZ) pairs (age 55.5 years, SD=6.5). A complete ophthalmological exam was performed for all subjects to exclude all those having ocular pathologies, previous ocular surgery or moderate visual impairment. Ocular biometry (Lenstar LS900; Haag-Streit AG, Köniz, Switzerland) was used for measuring central corneal thickness (CCT), lens thickness (LT), eye axial length (AL), anterior chamber depth (ACD), posterior chamber depth (PCD) and white-to-white (WW). A research prototype based in the recording and analysis of Purkinje images was used to measure the angle kappa (k). Only data from the left eye was compared. Intraclass Correlation Coefficients (ICC) were used as a descriptive statistics of twin resemblance and genetic models were fitted to estimate heritability.
Results : After adjusting for age and gender, all the evaluated parameters showed much higher ICCs between siblings for MZ twins (>0.9) than for DZ twins (<0.6). The ICC for angle kappa was 0.62 in MZ and 0.38 in DZ twins.All the models represented a major impact of genetics (AE; h>0.8) on ocular dimensions, although for angle kappa was a slightly lower (h=0.67).
Conclusions : Correlations of the estimation of ocular dimensions and kappa angle were much higher in the groups of identical twins. These results confirm that the variance of ocular dimensions and geometrical parameters are mainly genetically driven,including the natural deviation of the ocular optics of healthy eyes in middle-aged adults.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.