In vivo macular pigment measurements: a comparison of resonance Raman spectroscopy and heterochromatic flicker photometry

Aim: To investigate whether two methods of measuring macular pigment-namely, heterochromatic flicker photometry (HFP) and resonance Raman spectroscopy (RRS)-yield comparable data. Methods: Macular pigment was measured using HFP and RRS in the right eye of 107 participants aged 20 79 years. Correlations between methods were sought and regression models generated. RRS was recorded as Raman counts and HFP as macular pigment optical density (MPOD). The average of the top three of five Raman counts was compared with MPOD obtained at 0.5 eccentricity, and an integrated measure (spatial profile; MPODsp) computed from four stimulus sizes on HFP. Results: The coefficient of variation was 12.0% for MPODsp and 13.5% for Raman counts. MPODsp exhibited significant correlations with Raman counts (r=0.260, p=0.012), whereas MPOD at 0.5 did not correlate significantly (r=0.163, p=0.118). MPODsp was not significantly correlated with age (p=0.062), whereas MPOD at 0.5 was positively correlated (p=0.011). Raman counts showed a significant decrease with age (p=0.002) and were significantly lower when pupil size was smaller (p=0.015). Conclusions: Despite a statistically significant correlation, the correlations were weak, with those in excess of 90% of the variance between MPODsp and Raman counts remaining unexplained, meriting further research.