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Cord Huchzermeyer, Juliane Schlomberg, Ulrich Welge-Lüssen, Tos TJM Berendschot, Jan Kremers; Heterochromatic Modulation Photometry can be used to measure Macular Pigment Optical Density. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4066.
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© ARVO (1962-2015); The Authors (2016-present)
Macular pigment optical density (MPOD) can be measured psychophysically by comparing the luminance ratio between a short-wavelength and a long-wavelength light at a central and a peripheral retinal locus using heterochromatic flicker photometry (HFP). Heterochromatic modulation photometry (HMP) is a psychophysical test that uses, in contrast to HFP, test fields with constant mean luminance and chromaticity. To study whether HMP is suitable for measuring MPOD, we compared a custom made HMP protocol with measurements using HFP and macular pigment reflectometry (MPR).
We developed a protocol for the measurement of MPOD using a Maxwellian view LED stimulator. Two lights (B: 460nm and R:660nm, retinal illuminance of 21 phot Td each) were modulated in counterphase in a 2° center-field surrounded by a 12° white background (587 phot Td). Flicker detection threshold contrasts were determined for 9 different contrast ratios (B/R) of the two lights, varying between 10-1 and 101. Thresholds were determined using two randomly interleaved staircases and a 2AFC (flicker/no flicker) procedure. The measurements were repeated with central and with 6° nasal fixation. For comparison, MPOD was also measured using an HFP-based Macular Densitometer (Macular Metrics, USA) and the Macular Pigment Reflectometer (Maastricht Instruments bv, The Netherlands). The right eyes of 14 normal subjects were measured.
Log sensitivity (1/threshold) vs log B/R can be described by a V-shaped curve with a minimum at log B/R = 0 for the standard observer with Vλ-like spectral luminosity. A horizontal shift (along the log B/R axis) of the minimum represents a deviation from the Vλ. The difference of the positions of the minima measured at central and 6°nasal fixation were used to estimate the MPOD. MPOD measurements using HMP correlated with HFP (n=12, r=0.79, p<0.01) and MPR (n=13, r=0.69, p<0.05). Bland-Altman plots showed a marked systematic difference: HMP yielded 0.27±0.19 lower values than MPR. Agreement with HFP was much better (difference 0.02±0.13). HFP measured higher values in eyes with low MPOD and lower values in eyes with high MPOD.
HMP measurements agree well with HFP, but HMP has the advantage of using constant mean luminances and chromaticities. HMP also correlates with MPR, but there are systematic differences. This pilot study showed that the HMP method can be used to measure MPOD.
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