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Michael Engles, Billy R. Hammond, Billy R. Wooten; Macular pigment and contrast sensitivity: Testing the acuity hypothesis. Journal of Vision 2008;8(17):14. doi: 10.1167/8.17.14.
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© ARVO (1962-2015); The Authors (2016-present)
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 long-wave light. Previous tests of this hypothesis have an insufficient number of subjects (typically only two), have neglected to measure MP optical density, or have only tested the highest spatial frequencies of the greater contrast sensitivity function (CSF). To adequately test the Acuity Hypothesis, a specially designed optical apparatus was constructed and a rigorous psychophysical procedure was used. Complete CSFs could be obtained in broadband achromatic light (unfiltered xenon; attenuated by the MP) and in shortwave-deficient light (bandpass filter with a 550nm cutoff; not attenuated by MP). The results of this study do not support the predictions of the Acuity Hypothesis, and our findings are in agreement with those of previous studies. This is not to say that the MP does not influence visual function in other contexts (e.g. the visibility of distant targets as viewed through Earth's atmosphere). To this end, measuring CSFs in the presence of simulated blue haze carefully matched to sky light is already underway.
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