Macular Pigment: Testing the Acuity and Visibility Hypotheses

by MICHAEL ENGLES (Under the Direction of Billy R. Hammond, Jr.) ABSTRACT The macular pigment (MP) is composed of diet-derived carotenoids that screen blue light and are concentrated in and around the fovea. Several functions for the MP have been proposed. The earliest hypothesis, termed the Acuity Hypothesis, predicts that increased MP optical density should improve spatial vision by reducing the deleterious effects of chromatic aberration, an optical phenomenon whereby short-wave light is blurred to a much greater extent than longwave light. In light of the fact that the atmosphere preferentially scatters short-wave light, termed blue haze, Wooten & Hammond (2002) proposed the Visibility Hypothesis. They assert that increased MP optical density should improve distance vision by selectively reducing the veiling effects of short-wave veiling light such as “blue haze.” These two hypotheses have been tested using a specially designed optical device and a rigorous psychophysical procedure. The results do not support the Acuity Hypothesis, however our results do support the Visibility Hypothesis. Future testing should work toward establishing a causal relation between MP optical density and CS by supplementing subjects with lutein and zeaxanthin.