Race, iris color, and age-related macular degeneration

While most observers agree that age-related macular degeneration (AMD) is much more common in white persons than in persons of black African ancestry, the influence of iris color has been more controversial. We reexamined relationships between race, iris color, and AMD in a series of patients from our retina clinic.

We evaluated, in masked fashion, stereoscopic photographs of the retinas and irides in 306 sequential patients 60 years of age or older from our retina clinics. Four readers judged whether AMD was present, absent, or questionable in the retinal photographs and labeled iris color as blue, hazel, or brown. Presence or absence of AMD and presence and severity of the various macular lesions were determined by "majority vote" of the readers. We evaluated inter-rater agreement using the kappa statistic. We compared the prevalence of AMD and of specific AMD lesions as a function of race, sex, and iris color by contingency table analysis.

The kappa statistic showed good inter-observer agreement, being 0.466 (P < 10(-6)) for definite or questionable AMD and ranging from 0.185 to 0.522 (P = 0.0047 to P < 10(-6)) for most lesions. We found significantly more AMD in white patients than in black patients (X2 = 27.54, P < 10(-4)). There was no significant difference in AMD prevalence by sex. In white patients, AMD was significantly more prevalent in individuals with blue or hazel irides than in those with brown irides (X2 = 15.04, P = .02).

We confirm previous findings of a higher prevalence of AMD in white persons than in black persons. We also agree with those observers who claim that white subjects with light-colored irides have a higher prevalence of AMD than those with dark-colored irides. We suggest that differences in the association between iris pigmentation and AMD in different studies using different research methods may reflect genetic difference in the groups being studied.