Iris colour and age-related macular maculopathy in the EUREYE study

Purpose: To investigate the association of iris colour with grade and type of age-related maculopathy (ARM). Methods: Randomly sampled people (N=4760) aged 65 and over, participated in an eye examination and risk factor assessment in seven study centres across Europe (Norway, Estonia, UK, France, Italy, Greece and Spain). Two non-simultaneous 350stereoscopic colour fundus images centred were taken for each eye and graded at a single reading centre using the International ARM Epidemiological Study Group classification based on the grading of ARM in five mutually exclusive stages in the worst eye. Iris colour was documented by a picture with the same fundus camera focused on the iris and graded as blue, intermediate or brown according to standard images. Multinomial logistic regression models were used to examine the association between iris colour and ARM. Results: Blue iris colour was the predominant type (53%); 38% were brown and 9% intermediate (grey/green). Brown eyes were more common in southern Europe. There were no differences between men and women in eye colour distribution; the older age groups tended to have slightly higher proportions of blue eyed people in both men and women and in all countries. Unadjusted results showed a small excess of intermediate eye colour in the earliest stage of ARM (stage 1) (RRR=1.23, 95% CI 1.03 to 1.47) while brown iris colour showed a non significant protective association with stage 3 (RRR= 0.62, 95% CI 0.37 to 1.02). There was no association of iris colour with neovascular AMD but brown iris colour was significantly associated with Geographic AMD (RRR= 0.52, 95% CI 0.26 to 0.88). The magnitude of these associations was not altered by adjustment for age, sex, country or smoking. Conclusions: In this older European white population, brown iris colour appeared to significantly protect against atrophic AMD. We cannot exclude the possibility of uncontrolled confounding by other factors associated with iris colour.