EYE COLOR CHANGES PAST EARLY-CHILDHOOD - THE LOUISVILLE TWIN STUDY

Objective: To determine whether eye color changes after 6 years of age . Design: Longitudinal data on eye color were obtained from the Louisv ille Twin Study, Louisville, Ky. Twins (n = 1513 [individuals]) were a ssessed at least once and most twins (n = 1386) were examined on 2 or more occasions. Parents of twins were also examined at the study incep tion, 128 of whom were assessed again from February 1989 to October 19 93. Main Outcome Measure: Eye color was assessed at each examination b y matching the iridial coloration of the subject to 1 of 15 painted gl ass eye anterior segments, similar to those in artificial eyes, mounte d on a circular disk. The spectrum ranged from light blue (1) to dark brown (15). Results: Among whites (n = 1359), the eye color of 3.8% to 8.6% of the sample twins became 2 U or more darker or 2 U or more lig hter during 3- to 9-year intervals between 6 years of age and adulthoo d (> 18 years, < 24 years). Among identical (monozygotic) twin pairs, there was a high degree of concordance in eye color (r = 0.98 [P < .00 1]), while in fraternal (dizygotic) twin pairs, the concordance was le ss pronounced (r = 0.49) and decreased with age (r = 0.07). Among the sample of the mothers of twins, 9% had irides that lightened by 2 U or more during the follow-up period. Conclusion: Most individuals achiev e stable eye color by 6 years of age. However, a subpopulation of 10% to 15% of white subjects have changes in eye color throughout adolesce nce and adulthood in the eye color range that can be expected to refle ct changes in iridial melanin content or distribution. These data also suggest that such changes in eye color, or the propensity to such cha nges, may be genetically determined.