Effect of iris pigmentation of blue and brown eyed individuals with European ancestry on ability to see in low light conditions after a short-term dark adaption period

Abstract

The effect of iris depigmentation on ability to see in low light conditions has not been thoroughly investigated as an adaptive advantage that could have contributed to the evolution and persistence of blue eyes in Europe. In this study 40 participants took part in a simple eye test in increasing luminance to examine if there was a difference in capacity to see in low light conditions between blue and brown-eyed individuals after a brief adaptation period. Blue eyed individuals were identified to have significantly better ability to see in lower lighting after a short adaption period than brown eyed individuals making it likely depigmented irises provide an adaptive advantage (p=0.046). Superior ability to see in low light conditions could be the result of increased straylight in depigmented irises, which in light luminance is disadvantageous but in low light conditions may provide an advantage. More research is needed to determine the specific association between melanin content and low-light visual acuity. Furthermore, more research is needed to establish that the improved capacity of blue-eyed individuals to see in low light settings seen in this study is attributable to iris pigmentation rather than corresponding pigmentation elsewhere.