B R Hammond1, B R Wooten, D M Snodderly. 1. Vision Science Laboratory, College of Arts and Sciences, Arizona State University West, Phoenix 85069-7100, USA.
Abstract
PURPOSE: The authors investigated how individual differences in macular pigment (MP) density are related to loss of visual sensitivity with age. METHODS: Macular pigment and visual sensitivity of 27 healthy older subjects (aged 60-84 years) were compared with data from 10 younger subjects (aged 24-36 years). Macular pigment density was measured psychophysically with a centrally fixated stimulus 1 degree in diameter. Photopic increment sensitivity in the fovea was measured as thresholds for centrally fixated 1 degree stimuli on a bright yellow background. Foveal sensitivity of the pi-1 mechanism driven by the S cones was measured with 440-nm light. Photopic increment thresholds not determined by the pi-1 mechanism were measured with 550-nm light. Sensitivity was specified at the photoreceptor outer segments by individually correcting for psychophysically determined lens density and MP density. Dark-adapted (scotopic) sensitivity of rod-dominated visual mechanisms was measured in the parafovea with 550-nm light at 8 degrees eccentricity. RESULTS: Consistent with past reports, photopic sensitivity declined significantly with age for both 440-nm (P < 0.025) and 550-nm (P < 0.0003) light. For older subjects, photopic sensitivity was positively related to MP density, although more strongly for 440-nm (P < 0.001) than for 550-nm (P < 0.01) light. Parafoveal scotopic sensitivity of the older subjects was also positively related to MP density (P < 0.02). Visual sensitivity of the young subjects was not significantly related to MP density. CONCLUSIONS: For subjects older than 60 years, visual sensitivity of those with high MP density was not significantly different from that of young subjects. Conversely, older subjects with low MP density had lower sensitivity than young subjects. Although this study cannot prove causality, the results show that high MP density was associated with the retention of youthful visual sensitivity, which suggested that MP may retard age-related declines in visual function.
PURPOSE: The authors investigated how individual differences in macular pigment (MP) density are related to loss of visual sensitivity with age. METHODS: Macular pigment and visual sensitivity of 27 healthy older subjects (aged 60-84 years) were compared with data from 10 younger subjects (aged 24-36 years). Macular pigment density was measured psychophysically with a centrally fixated stimulus 1 degree in diameter. Photopic increment sensitivity in the fovea was measured as thresholds for centrally fixated 1 degree stimuli on a bright yellow background. Foveal sensitivity of the pi-1 mechanism driven by the S cones was measured with 440-nm light. Photopic increment thresholds not determined by the pi-1 mechanism were measured with 550-nm light. Sensitivity was specified at the photoreceptor outer segments by individually correcting for psychophysically determined lens density and MP density. Dark-adapted (scotopic) sensitivity of rod-dominated visual mechanisms was measured in the parafovea with 550-nm light at 8 degrees eccentricity. RESULTS: Consistent with past reports, photopic sensitivity declined significantly with age for both 440-nm (P < 0.025) and 550-nm (P < 0.0003) light. For older subjects, photopic sensitivity was positively related to MP density, although more strongly for 440-nm (P < 0.001) than for 550-nm (P < 0.01) light. Parafoveal scotopic sensitivity of the older subjects was also positively related to MP density (P < 0.02). Visual sensitivity of the young subjects was not significantly related to MP density. CONCLUSIONS: For subjects older than 60 years, visual sensitivity of those with high MP density was not significantly different from that of young subjects. Conversely, older subjects with low MP density had lower sensitivity than young subjects. Although this study cannot prove causality, the results show that high MP density was associated with the retention of youthful visual sensitivity, which suggested that MP may retard age-related declines in visual function.
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