LAUSR

Dear Editor, T he Newborn Eye Screening Test (NEST) study is a prospective cohort study that aims to determine the prevalence of ophthalmic diseases at birth at Lucile Packard Children’s Hospital at Stanford University School of Medicine. Our prior study demonstrated the predominance of brown iris coloration during the first year of the NEST study (Ludwig et al. 2016). Here, we aim to assess the change in iris colour over a 2-year follow-up period. This study was approved by the Institutional Review Board and Ethics Committee at Stanford University. All participants screened during the first year of enrolment, were called and asked to assess their newborns’ eye colour 2 years after hospital discharge. The follow-up iris colour and updated demographic data were compared with the images which had been reviewed by paediatric vitreoretinal specialist (DMM) within the first few days of birth. Of the 202 newborns enrolled in NEST within the first year, 148 (73%) responded at 2-year follow-up. Brown was the most prevalent primary iris colour (52.0%, 77/148, Table 1) and was less likely to change over time compared to non-brown iris colours (brown to brown, 94%, 73/77). There was a higher frequency of change from blue to non-blue iris colours (blue to brown 27%, 11/40, blue to hazel 7.5%, 3/40 and blue to green 5%, 2/40; p value < 0.001). We found no significant difference in the pattern of iris colour change as a function of gender (p = 0.861). Regarding race, at birth, the prevalence of blue irides was significantly higher among White/Caucasian, Native Hawaiian or Pacific Islander indicating a significant difference in distribution of iris colour between races (p < 0.001) (Ludwig et al. 2016). The same significant difference in distribution of iris colours is also seen at 2-year follow-up in the present study (p < 0.001). Our results indicate that iris colour did not change over the 2 years’ follow-up period in most cases (66.9%), and only the iris colour of 3.4% (5/148) of subjects became lighter from brown to hazel/ green, from partial heterochromia to blue and from complete heterochromia to blue. Similarly, the Louisville Twin Study revealed that iris colour stabilizes by 6 years of age in most children. However, they noted that iris colour continues to change throughout adolescence and until adulthood in a subpopulation of 10–20% of twins (Bito et al. 1997). The present study, however, is the first to follow iris colour changes from shortly after birth to 2 years of age. Though a significant association between age and gender on iris colour was seen previously in a large cross-sectional study (Liu et al. 2010), no statistically significant correlations between iris colour, ethnicity, sex, gender, multiplicity and being the first-born child were observed in our study. As predicted, the distribution of iris colour at 2-year follow-up was significantly related to race. While families tend to identify the iris colour of their newborns, physicians should also monitor the iris colour of their patients. Changes in iris colour may reveal signs of pathology such as neurofibromatosis, Down syndrome, herpes simplex, pigment dispersion, albinism or primary melanocytic tumours of the iris (Mackey et al. 2011). To our knowledge, this is the first study to evaluate the frequency of subjective change in iris colour from birth to 2 years of age. Overall, we report a low rate of subjective change in iris colour from birth to 2 years of age among newborns with brown eyes and a slightly higher rate of change among newborns with blue eyes.