Eye color changes past early childhood. The Louisville Twin Study
L. Z. Bito, A. Matheny, K. J. Cruickshanks, D. M. Nondahl and O. B. Carino
Department of Ophthalmology, Columbia University, New York, NY, USA.
OBJECTIVE: To determine whether eye color changes after 6 years of age.
DESIGN: Longitudinal data on eye color were obtained from the Louisville
Twin Study, Louisville, Ky. Twins (n = 1513 [individuals]) were assessed at
least once and most twins (n = 1386) were examined on 2 or more occasions.
Parents of twins were also examined at the study inception, 128 of whom
were assessed again from February 1989 to October 1993. MAIN OUTCOME
MEASURE: Eye color was assessed at each examination by matching the iridial
coloration of the subject to 1 of 15 painted glass eye anterior segments,
similar to those in artificial eyes, mounted 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 lighter during 3- to 9-year intervals
between 6 years of age and adulthood (> 18 years, < 24 years). Among
identical (monozygotic) twin pairs, there was a high degree of concordance
in eye color (r = 0.98 [P < .001]), while in fraternal (dizygotic) twin
pairs, the concordance was less 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 achieve stable eye color by 6 years of age. However, a
subpopulation of 10% to 15% of white subjects have changes in eye color
throughout adolescence and adulthood in the eye color range that can be
expected to reflect changes in iridial melanin content or distribution.
These data also suggest that such changes in eye color, or the propensity
to such changes, may be genetically determined.
