title: In vivo macular pigment measurements: a comparison of resonance Raman spectroscopy and heterochromatic flicker photometry.
abstract: OBJECTIVE
  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 degrees 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 degrees 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 degrees 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.
authors.affiliation: Department of Ophthalmology, Queen's University Belfast BT12 6BA, UK. r.e.hogg@qub.ac.uk
authors.forename: R E
authors.initials: RE
authors.lastname: Hogg
authors.forename: R S
authors.initials: RS
authors.lastname: Anderson
authors.forename: M R
authors.initials: MR
authors.lastname: Stevenson
authors.forename: M B
authors.initials: MB
authors.lastname: Zlatkova
authors.forename: U
authors.initials: U
authors.lastname: Chakravarthy
mesh_terms: D000328:Adult; D017677:Age Distribution; D000368:Aged; D000375:Aging / Q000502:physiology; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D008266:Macula Lutea / Q000737:chemistry*; D008297:Male; D008875:Middle Aged; D010783:Photometry / Q000379:methods; D015203:Reproducibility of Results; D012168:Retinal Pigments / Q000032:analysis*; D012307:Risk Factors; D013059:Spectrum Analysis, Raman / Q000379:methods
chemical_list: D012168:Retinal Pigments