title: Investigation of the effect of simulated lens yellowing, transparency loss and refractive error on in vivo resonance Raman spectroscopy.
abstract: OBJECTIVE
  To separately investigate the impact of simulated age-related lens yellowing, transparency loss and refractive error on measurements of macular pigment (MP) using resonance Raman spectroscopy.
  
  
  METHODS
  Two healthy young subjects with clear media underwent Raman spectroscopy under the following conditions: age-related lens yellowing was simulated using seven broad-band yellow filters with transmittance at 488 nm ranging from 0.54 to 0.90; cataract was simulated using five white filters of increasing opacity (scatter filters), the transmittance of which ranged from 0.42 to 0.86, each of which reduced peak contrast sensitivity by approximately 0.1 log units over the previous filter. Refractive error up to +6.25 D was achieved using soft contact lenses.
  
  
  RESULTS
  The Raman signal declined steadily to an average value of 43% of the starting value with the densest yellow filter in place. The white scatter filters produced a progressive linear reduction in signal resulting in almost complete signal loss with the densest filter. Refractive error resulted in an initial slight improvement in Raman count up to a value of +2.00 D followed by a decline thereafter.
  
  
  CONCLUSIONS
  These results imply that lens yellowing and increasing scatter has an influence on the Raman signal and suggest that studies using this technology to estimate MP levels in older populations should carefully account for the status of the lens.
authors.affiliation: Department of Ophthalmology and Vision Science, Queen's University, Belfast, UK. r.e.hogg@qub.ac.uk
authors.forename: R E
authors.initials: RE
authors.lastname: Hogg
authors.forename: M B
authors.initials: MB
authors.lastname: Zlatkova
authors.forename: U
authors.initials: U
authors.lastname: Chakravarthy
authors.forename: R S
authors.initials: RS
authors.lastname: Anderson
mesh_terms: D000328:Adult; D000375:Aging / Q000502:physiology*; D006801:Humans; D007908:Lens, Crystalline / Q000502:physiology*; D014975:Lutein; D008268:Macular Degeneration; D012029:Refraction, Ocular / Q000502:physiology*; D013059:Spectrum Analysis, Raman; D024341:Xanthophylls; D065146:Zeaxanthins
chemical_list: D024341:Xanthophylls; D065146:Zeaxanthins; D014975:Lutein