Purpose
To ascertain which retinal vascular features have strong genetic influences. The retinal vascular features examined herein are central retinal artery and vein equivalents (CRAE and CRVE) and arteriolar:venular ratio (AVR).
Methods
Obtained from the Minnesota Study of Twins Reared Apart (MISTRA) registry, color fundus photographs of 66 pairs of monozygotic (MZA) and 40 pairs of dizygotic (DZA) twins reared apart were digitized from film slides at 600 DPI. The images were then graded using the software packages IVAN (Interactive Vessel Analyzer), v1.3 (courtesy of Dr. Nicola Ferrier of the Univ. of Wisconsin - Madison School of Engineering and the Dept. of Ophthalmology and Visual Sciences) and VAMPIRE (Vascular Assessment and Measurement Platform for Images of the Retina, available at vampire.computing.dundee.ac.uk). One grader performed all of the analysis with each software package.
Results
Demographics: A total of 212 eyes from 53 pairs of twins (33 MZA pairs and 20 DZA pairs) were used. Average age (yrs) at imaging (mean ± stdandard deviation) for the included subjects was 38.0±13.8 MZA and 42.2±13.9 for DZA. 69.7% of the MZA and 65.0% of the DZA were female.<br /> Image Analysis: Of the 112 MZA images processed, 2 were ungradeable by IVAN. Of the 180 DZA images processed, 2 were ungradeable by IVAN and 1 by VAMPIRE. IVAN measurements showed no significant difference between MZA and DZA groups for mean CRAE, CRVE, or AVR. Comparison of average intertwin absolute differences in CRAE (MZA: 11.8±7.7, DZA: 20.3±13.5) showed significantly greater concordance between MZA pairs than DZA pairs (p=0.008). The same relationship was evident in a comparison of intertwin AVR differences (MZA: 0.0094±0.023, DZA: 0.052±0.047). The same comparison for CRVE (MZA: 10.8±9.5, DZA: 12.7±13.0) was nonsignificant between MZA and DZA pairs (p=0.29).
Conclusions
In a unique cohort of twins reared apart, there is greater concordance between MZA twins than DZA twins for CRAE and AVR, but not CRVE. This suggests that CRAE and apparent AVR are more heritable than CRVE.