Purchase this article with an account.
T. T. Berendschot, R. L. P. van der Veen, M. Makridaki, D. Carden, I. J. Murray; A Comparison of Psychophysical and Optical Methods for Determining the Spatial Profile of Macular Pigment. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1725.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To investigate the origin of the discrepancies between psychophysical and optical methods of measuring Macular Pigment Optical Density by comparing MPOD at different eccentricities.
MPOD reflectometry estimates were obtained at 0, 1, 2, 4, 6 and 8 degrees eccentricity with the Macular Pigment Reflectometer (MPR), that also allowed separate determination of lutein and zeaxanthin. The Macular Pigment Screener (MPS, called QuantifEYE in the USA) was used to assess MPOD psychophysically at 0, 0.5, 1, 2, 3, 4, 6 and 8 degrees eccentricity. In contrast with the more conventional approach of adjusting a luminance ratio until flicker is eliminated, it employs a new technique for obtaining the minimum flicker point whereby observers press a button when they detect flicker.
Spatial MPOD profiles were compared in 19 healthy individuals aged 26 ± 8 years. We assumed an exponential decay for both the lutein and zeaxanthin distribution and determined these spatial distributions from our MPR data, that measure the average over a 1 degree field. The sum of these resembles the actual MPOD profile. For all eccentricities greater than 1 degree there was very good agreement between these values and the MPOD estimates obtained by the MPS, that employed an 1 degree test field (r = 0.94, p < 0.001). Note that we added the MPOD estimate from the MPR data at 8 degrees eccentricity to all MPS estimates, since in the latter the value at 8 degrees is taken as the reference point. For the 0 and 0.5 degree measurements the agreement was poor. In order to account for the difference between the two techniques at 0 and 0.5 degrees we assumed that on average, observers set flicker thresholds using a point at about 0.4 degrees of the flickering target when the 1 degree target was presented at 0 degrees, and at about 0.9 degrees when the 1 degree target was presented at 0.5 degrees from the centre. After these corrections there was a high correlation between the values obtained with the two techniques. (r = 0.87, p < 0.001).
The psychophysical measurement of MPOD can be corrected by assuming that flicker thresholds are based on observers fixating close to the edge of the flickering target at 0 and 0.5 degrees eccentricity. At other eccentricities, flicker thresholds are not based on this so called edge strategy and resulting MPOD measurements are virtually indistinguishable from those obtained with the optical technique.
This PDF is available to Subscribers Only