Macular pigment assessment by motion photometry

A Moreland anomaloscope was modified to measure macular pigment optical density (MPOD) profiles by motion photometry. A grating (spatial frequency 0.38 c deg−1), whose alternate bars were filled, respectively, with 460 nm (maximum MP absorption) and 580 nm (zero MP absorption) lights, drifted steadily at 37° s−1. The subject adjusted the 580 nm radiance to minimise perceived motion (equiluminance between 460 and 580 nm). Five or more settings were made for two foveal fields (0.9° and 2.2° diameter) and 11 extrafoveal annular fields (0.8°–7.5° eccentricity). Twenty subjects made measurements for both eyes: some with replications. MPOD profiles varied in scale (0.18–0.75 for the 0.9° foveal field) and in shape. A mean profile was derived. Foveal data were optimally aligned with annular data in that profile when plotted at 0.71 of the foveal field radius. Factors that limit precision were identified, such as fixation errors foveally and Troxler’s effect parafoveally.