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Richard A Bone, Jorge C Gibert, Anirbaan Mukherjee; Three Characteristics of the Central Macula: Light, AMD, and Macular Carotenoids. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3480.
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To determine the cumulative distribution of light on the retina over extended periods under quasi-natural viewing conditions. Our hypothesis was that the light distribution would peak in the center of the macula, thereby offering a potential explanation for the role of light in age-related macular degeneration as well as the role of macular pigment in providing protection.
An eye-tracker was used to obtain a time record of the spatial distribution of light in the subject's field of view as well as the subject's gaze position. A corresponding time record of the distribution of light on the retina was calculated. Five informed subjects were employed in feasibility tests and 58 naïve subjects participated in 5 experimental phases: 1) Subjects viewed a gray-scale image, 2) they observed a sequence of photographic images, 3) they viewed a video 4) they worked on a computer, 5) they walked around freely. The informed subjects were instructed to gaze at bright objects in the field of view and then at dark objects. Naïve subjects were allowed to gaze freely for all phases.
In Phase 4, light distributions peaked at the fovea for all subjects. Combining the results of the other phases, 74% of subjects showed an overall increase in retinal illuminance at or around the fovea (33% with a sharp increase at the fovea, 41% with a broader distribution) and 26% showed a peak illuminance elsewhere in the retina. Combining all phases, 77% of subjects spent more time viewing brighter objects in the field of view (39% showed a sharp increase in illuminance at the fovea, 38% with a broader distribution around the fovea). Under head-restraint conditions, subjects generally spent more time fixating bright features in the field of view. Under unrestricted conditions (i.e. subjects walking freely), the distribution of light peaked in the inferior retina.
Prior to this study, the distribution of light on the retina was unknown except under unnatural Ganzfeld illumination. Our results partially support our hypothesis that the cumulative light distribution is maximum in the central macula. In particular, using a computer consistently resulted in a peak at the center of the retina. The study has also shown that some individuals spend more time fixating on bright objects in the field of view. In these cases, there may be increased risk of AMD. By screening excessive light, macular pigment may lessen this risk.
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