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Erschienen in:
01.12.2006 | Clinical Investigation
Macular pigment optical density measurement in autofluorescence imaging: comparison of one- and two-wavelength methods
Erschienen in: Graefe's Archive for Clinical and Experimental Ophthalmology | Ausgabe 12/2006
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Background
Measurement of macular pigment (MP) can be performed by analysis of autofluorescence (AF) images. These can be obtained by standard 488-nm argon-imaging alone (one wavelength, 1-Λ) or with additional digital subtraction of a second image at 514 nm (two wavelengths, 2-Λ). The analyses are easy to perform, and we present a comparison of both methods and investigate their reliability and repeatability.
Methods
Inter-individual variability of MP optical density (MPOD) measurements was assessed in single eyes of 120 subjects with a modified Heidelberg retina angiograph (HRA). MPOD values obtained with one (488 nm) Λ (MPOD1Λ) were compared with those obtained with two (488 nm and 514 nm) Λ (MPOD2Λ). To test the repeatability of the two methods, 20 subjects were subjected to five repeated measurements.
Results
Among 120 individuals, mean MPOD1Λ at 0.5° eccentricity was 0.59 (range 0.06–1.32), mean MPOD2Λ was 0.5 (range 0.01–1.21). Apart from this systematic difference, 1-Λ and 2-Λ measurements at 0.5° agreed well across the range of MPOD values (β=0.964, 95% CI 0.891–1.096; R=0.83). At 2° around the fovea, a systematic difference (0.11) was accompanied by declining agreement at higher MPOD values (β=0.669, 95% CI 0.519–0.844; R=0.48). Among 20 subjects with five repeated measurements, the reliability ratio was 0.97 for 1-Λ and 0.94 for 2-Λ at 0.5° and 0.93 and 0.94, respectively, at a distance of 2°.
Conclusions
Both methods showed a high repeatability with little influence of measurement error. They agree well at the fovea centre in terms of ranking individuals according to their MPOD, but provide increasingly deviating results at a distance of 2° around the fovea, probably because the 1-Λ method, in contrast to the 2-Λ method, cannot compensate for disruptive influences and for heterogeneous distributions of the lipofuscin fluorophores. The 1-Λ method can be performed by standard HRA and could therefore be used for screening in multicentre studies, but only approaches the actual amounts of MP. The 2-Λ method remains the more precise method for MPOD measurement in autofluorescence imaging.