Identifying Genetic Components of Visual Function - A Classical Twin Study

Abstract

Purpose:: This study sought to assess the relative genetic contribution of various aspects of visual function using a classical twin study.

Methods:: Monozygotic (MZ) and dizygotic (DZ) twin pairs without evidence of manifest eye disease and corrected visual acuity better than 6/7.5 were recruited from a sample of population-based volunteer twins. In each subject contrast thresholds (luminous flicker and isoluminant Red and Blue color) were measured on a background that produced >1100 Troland to evaluate aspects of cone visual function under steady state conditions. Dark adaptation dynamics were determined from the rod-cone break (RCB) returned from a tracking method following bleach of 30% photopigment.

Results:: Sixteen MZ and 16 DZ twin pairs were recruited and examined in this twin study. The mean age of subjects was 67 ± 5 years (range 53-77 years). Inter-pair correlations [2.5% to 95% CL] for all steady state conditions were significantly greater (p<0.05) between MZ twin pairs than they were for the DZ pairs (spatiotemporal: 4HZ rMZ=0.81 [0.48 to 0.91] vs rDZ=0.00 [-.53 to 0.53]:14Hz rMz=0.81 [0.51 to 0.93] vs rDz=-0.26 [-.68 to 0.29], Red threshold rMz=0.60 [0.12 to 0.85] vs rDZ=0.07 [-0.48 to 0.58], Blue threshold rMZ=0.58 [0.09 to 0.84] vs rDZ=0.10 [-.45 to 0.61]). Inter-pair correlations of the RCB were not significantly greater between MZ twin pairs than between DZ pairs (rMZ=0.68 [.0.14 to 0.91] vs rDZ0.54 [-0.26 to 0.90]). Inter-pair variability was significantly (p<0.05) greater between DZ observers compared with MZ pairs (F-ratio >3.8) in all cases except for the RCB (F-ratio=0.90, p=0.58).

Conclusions:: This study indicates that visual processes mediated by cones have a genetic predisposition. However, processes underlying dark adaptation are less dependent on genetic predisposition and more able to be influenced by environmental factors. These findings have implications for our understanding of pathogenic mechanisms and influences in macular diseases.

Keywords: genetics • aging: visual performance