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Journal of Biomedical Optics

Stimulus edge effects in the measurement of macular pigment using heterochromatic flicker photometry
Author(s): William E. Smollon; Billy R. Wooten; Billy R. Hammond
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Paper Abstract

Heterochromatic flicker photometry (HFP) is the most common technique of measuring macular pigment optical density (MPOD). Some data strongly suggest that HFP samples MPOD specifically at the edge of center-fixated circular stimuli. Other data have led to the conclusion that HFP samples over the entire area of the stimulus. To resolve this disparity, MPOD was measured using HFP and a series of solid discs of varying radii (0.25 to 2.0 deg) and with thin annuli corresponding to the edge of those discs. MPOD assessed with the two methods yielded excellent correspondence and linearity: Y=0.01+0.98X, r=0.96. A second set of experiments showed that if a disc stimulus is adjusted for no-flicker (the standard procedure) and simply reduced in size, no flicker is observed despite the higher level of MPOD in the smaller area. Taken together, these results confirm that MPOD is determined at the edge of the measuring stimulus when using stimulus sizes in the range that is in dispute (up to a radius of 0.75 deg). The basis for this edge effect can be explained by quantitative differences in the spatial-temporal properties of the visual field as a function of angular distance from the fixation point.

Paper Details

Date Published: 12 November 2015
PDF: 13 pages
J. Biomed. Opt. 20(11) 115004 doi: 10.1117/1.JBO.20.11.115004
Published in: Journal of Biomedical Optics Volume 20, Issue 11
Show Author Affiliations
William E. Smollon, Brown Univ. (United States)
Billy R. Wooten, Brown Univ. (United States)
Billy R. Hammond, The Univ. of Georgia (United States)


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