Primate foveas have a distinctive yellow macular pigment that is one of their recognized specializations. The long-term objectives of this application are to test two major nonexclusive hypotheses about the functional roles of the macular pigment. The first hypothesis states that the macular pigment aids in visual resolution in the fovea by absorbing scattered or poorly focussed blue light. A parallel series of experiments will be done with monkeys and humans to examine the relationship of the foveal pigmentation to visual resolution. Monkey retinas will be studied by densitometry, microscopy and image analysis. The macular pigment density distribution, and other foveal features will be characterized. These data will be used to refine monochromatic fundus photography for measuring the macular pigment density in vivo. Humans with high and low amounts of macular pigment measured by the in vivo technique will be compared on a demanding test of visual acuity. The test stimulus will be placed precisely at closely spaced intervals within the foveal avascular zone by image stabilization. An accurate profile of visual acuity in the fovea will be determined. If the resolution hypothesis is correct, humans with higher amounts of macular pigment should have better visual resolving power. The second hypothesis states that the macular pigment protects the fovea from damage by light and oxygen. Protection could occur by absorption of light, quenching of radicals, or breaking chain reactions leading to lipid oxidation. Absorption of light will be measured optically by microdensitometry and image analysis. In the same retinas the concentrations of lutein and zeaxanthin, the carotenoids that comprise the macular pigment, will be measured by high performance liquid chromatography. Serum and other tissues of the same individuals will also be analyzed for carotenoid concentrations. Retinas of monkeys with high and low amount of macular pigment will be assayed for lipid oxidation products. If macular pigment is protective, the retinas low in macular pigment should be subject to more oxidative damage and be higher in lipid peroxides. Two health-related results are expected. One is a description of visual acuity in the avascular zone of the fovea. This may be useful for establishing treatment criteria for mascular disease. The other outcome will be better understanding of one of the key factors that is thought to protect the macula from damage.
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