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J.M. Stringham, B.R. Hammond, B.R. Wooten, D.M. Snodderly; Compensation for Light Loss Due to Filtering by Macular Pigment . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1780.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Macular pigment (MP) lies anterior to the photoreceptors and filters short–wave light. At peak absorbance, this filtering can range from almost complete transmission to a low of about 3%. Due to the uneven topographical distribution of MP, variation in filtering would result in perceptual discontinuity if the visual system did not compensate for filtering differences across the central retina. This study describes that effect. Methods: 15 young subjects with widely varying MP density were assessed. For 10 subjects, increment thresholds were measured at 440 and 500 nm (using conditions chosen to isolate the π–1 mechanism) in the center of the fovea and at 6° eccentricity. For 5 subjects, increment thresholds were obtained for 440 nm light at 0, 1, 1.75 and 7° eccentricity. Yellow (575 nm)–blue (440 nm) cancellation functions were obtained for these same 5 subjects at the same eccentricities. MP spatial profiles were measured using HFP. Results: When considering the central versus peripheral loci, increment thresholds at 440 nm did not differ across sites (n =15, log relative sensitivity = 2.23 and 2.3, respectively) despite MP densities ranging from 0.02–1.0 log units. Hue cancellation values (the amount of yellow needed to cancel blue) also did not vary across test sites (n = 5). Conclusions: Despite large between–and– within subject–differences in the transmission of short–wave light by MP, short–wave sensitivity across the central retina was relatively constant. For example, one subject’s MP density declined from a central peak of 0.99 to near zero at 7° (near 95% transmission difference) yet color appearance (determined by hue cancellation) did not change. These results suggest that the visual system may increase gain to the short–wave system in order to offset light losses due to MP.
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