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J. Moreland, A.G. Robson, G.E. Holder, F.W. Fitzke; Physical and Biological Calibration of the Scanning Laser Ophthalmoscope: Measurement of Macular Pigment From Autofluorescence Images . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1782.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To validate optical density (OD) measurements of macular pigment made by single–wavelength fundus autofluorescence (AF) by comparison with those made by motion photometry. Methods: Macular pigment optical density was measured at 12 retinal locations in 10 subjects using minimum motion photometry comparing 460nm with 580nm. Relative OD was calculated as log (Rref/R), where Rref is the mean radiance of the 580nm comparison stimulus for the three most eccentric locations (5.4°, 6.6° and 7.4°) and R is the radiance setting at any location. AF images were obtained through a high–pass barrier filter (measured transmittance of 0.01 at 488nm) using a modified scanning laser ophthalmoscope. Grey–scale values of AF were calibrated in terms of OD over a stimulus range of approximately 2 log units for a fluorescent standard (SFS 225). The calibration was repeated using the human eye as a biological standard. OD was computed from mean calibrated grey scale values for a central circular area and for annular segments, topographically identical to areas tested psychophysically. Results: Physical and biological calibrations were in close agreement. Mean relative OD values obtained using the psychophysical and calibrated imaging methods were linearly related and gave peak values of between 0.2 and 0.8 (slope = 0.98, r2=0.97). A plot of the difference against the average (Bland and Altman, 1986) of the 120 individual AF and minimum motion measurements revealed a small consistent bias (mean difference = 0.02, S.D. = 0.052). This offset indicates that AF estimates require a mean downward correction of 0.02 to equate them with psychophysically obtained values; the limits of agreement (95% confidence levels) lie between –0.08 and 0.12 of minimum motion measurements. Conclusions: Assessment of MP optical density using single–wavelength fundus autofluorescence imaging correlates well with psychophysically derived values for topographically identical retinal locations.
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