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From: Tony (
Subject:         Re: Eye color
Date: July 10, 2014 at 11:21 pm PST

In Reply to: Eye color posted by Dejan on July 10, 2014 at 6:35 pm:

Eye Color Changes Past Early Childhood
The Louisville Twin Study
Laszlo Z. Bito, PhD; Adam Matheny, PhD; Karen J.
Cruickshanks, PhD; David M. Nondahl, MS; Olivia B.
Carino, OD
Arch Ophthalmol. 1997;115(5):659-663.
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 through-out 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.


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