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Raman detection of carotenoid pigments in the human retina

We have used resonant Raman scattering as a novel, non- invasive, in-vivo optical technique to measure the concentration of macular carotenoid pigments in the living human retina of young and elderly adults. Using a backscattering geometry and resonant molecular excitation in the visible, we measure the Raman peaks originating from the single- and double-bond stretch vibrations of the (pi) - electron conjugated molecule's carbon backbone. The Raman signals scale linearly with carotenoid content while the required laser excitation is well below safety limits for macular exposure. Measured macular pigment levels decline significantly with increasing age. The Raman technique is objective and quantitative and may lead to a new method for rapid screening of carotenoid pigment levels in large populations at risk for vision loss from age-related macular degeneration, the leading cause of blindness in the elderly in the United States.