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Max Snodderly, James Stringham; Macular Pigment Reduces Visual discomfort. Journal of Vision 2010;10(7):413. doi: 10.1167/10.7.413.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To determine the effect of macular pigment (MP) on the threshold of visual discomfort in young subjects Methods: A Maxwellian-view optical system was used. Six young (<35 yrs.), normal subjects with a wide range of MP densities (0.10-0.71 at 30' eccentricity) viewed monochromatic disks of light centrally, and parafoveally (7′ temporal retina). The psychophysical method of ascending limits was employed to determine discomfort thresholds at each wavelength. After extensive training, subjects were instructed to determine the point at which the intensity of the stimulus produced discomfort sufficient to make it difficult to view the light without an aversive response (e.g., squinting or averting the eyes). Discomfort thresholds were also obtained for xenon-white light (partially absorbed by MP), and a broadband yellow (outside the absorption band of MP).Spatial profiles of MP were measured psychophysically using heterochromatic flicker photometry (HFP).Individual lens densities were determined by subtracting subjects' scotopic sensitivity to lights of 410, 440, and 560 nm from the corresponding rhodopsin extinction coefficients. Results: For the central viewing condition, MP significantly reduced visual discomfort thresholds for short wavelengths (440-500 nm), compared to the parafoveal viewing condition. This reduction was commensurate with a subject's MP level. For the parafovea, a monotonic increase in discomfort sensitivity (1 / threshold) with decreasing wavelength was found for all subjects. In a linear fashion, subjects with higher MP levels were shown to tolerate more xenon-white relative to broadband yellow before reaching discomfort threshold. Conclusions: Short-wave lights produced the greatest visual discomfort, and centrally-viewed light was roughly twice as uncomfortable as light imaged on the parafovea. MP strongly attenuates visual discomfort. The spectral absorption and spatial distribution of MP increase the range of comfortable visual operation for the central retina, thereby facilitating visual performance as well as reducing risk of light damage.
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