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James Loughman, Stephen Beatty, Jim Stack, Eithne E. Connolly, John M. Nolan; Comparison Of Macular Pigment Optical Density Measurements Using Customised Heterochromatic Flicker Photometry Versus Reflectance. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3623.
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© ARVO (1962-2015); The Authors (2016-present)
To compare macular pigment optical density (MPOD) values obtained with two different MP measurement devices: the DensitometerTM and the Zeiss Visucam 200.
MPOD was measured on 25 subjects using both devices, and measurements for each subject were performed on the same day. Demographic, vision and lifestyle details were also recorded. The DensitometerTM, using customised heterochromatic flicker photometry (cHFP), is a psychophysical (subjective) technique, and provides data on MPOD and its spatial profile across the retina (i.e. 0.25, 0.5, 1.0, 1.75 and 3 degrees of retinal eccentricity). The Zeiss Visucam 200, using reflectance, is an optical (objective) technique, and provides data on maximum and mean MPOD across the retina.
The reflectance technique, when compared to the cHFP technique, yielded significantly higher readings for central (max) MPOD (mean difference = 0.122, 95% confidence interval 0.038 to 0.206, paired t-test) and significantly lower readings for average MPOD (mean difference = -0.106, 95% confidence interval -0.165 to -0.046, paired t-test). The limits of agreement on the Bland Altman plot are located at 0.4 units from the centre line in the case of central MP, and at 0.28 units in the case of average MP; both plots, therefore, suggest considerable discrepancies in measurements between the two devices for many subjects. In the case of average MP, the Bland Altman plot also conveys that the reflectance technique yields consistently lower estimates for all subjects with macular pigment above 0.3 units.
As the 95% confidence interval for the mean difference does not contain 0, for any of the comparisons made (i.e. central MPOD and average MPOD), we conclude that there is, on average, a significant difference in measurements yielded by the two methods and, therefore, these techniques should not be used interchangeably.
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