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O.M. O' Donovan, J. Nolan, K. Neelam, S. Beatty; Measurement of Macular Pigment: Raman Spectroscopy versus Heterochromatic Flicker Photometry . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1783.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: There are several techniques for measuring macular pigment (MP) in vivo, of which Raman spectroscopy (RS) is a recently developed objective method. This study reports Raman MP readings in terms of their reproducibility and test–retest variability, and in terms of their validity by comparing them with heterochromatic flicker photometry (HFP). Methods: MP was measured in 120 healthy subjects using HFP and RS, and the latter technique was also used on 2 separate occasions in a sample of 20 subjects in order to investigate inter–sessional variability of readings. Intra–sessional reproducibility of Raman MP measurements was also calculated. In addition, serum concentrations of lutein (L) and zeaxanthin (Z) were measured, and correlated with both RS and HFP MP readings. Results: Mean (± SD) MP for the right eye was 0.279 ± 0.145 and 0.319 ± 0.155 with RS and HFP, respectively. The differences between corresponding MP readings taken on RS and HFP lay within the Bland–Altman 95% limits of agreement for the two instruments in 93.6% and 94.4% of cases for right and left eyes, respectively. Intra–sessional reproducibility of Raman readings, expressed in terms of the coefficient of variation, was 8.42 ± 7.12 %. Ninety–five percent of MP readings taken with RS on two separate occasions lay within the 95% limits of agreement for the two sessions. A positive, but insignificant, relationship was observed between Raman (and HFP) MP values and serum concentrations of L (and Z) (RS: p = 0.356; HFP: p = 0.540). Conclusions: Raman spectroscopy, an objective method of measuring MP levels in vivo, exhibits acceptable reproducibility and test–retest variability. We have demonstrated good correlation between RS and HFP readings of MP, thus authenticating Raman spectroscopy against a validated psychophysical technique of measuring MP. However, investigators should use only one of these instruments for the duration of any given study because of differences in the scientific rationale, and the factors that influence RS and HFP measurements of MP.
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