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W. Gellermann, M. Sharifzadeh; Comparison of Resonance Raman and Autofluorescence Imaging for the Measurement of Human Macular Pigment Distributions. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2130. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Resonance Raman and autofluorescence excitation spectroscopy are two distinctly different optical methods capable of quantifying and imaging the spatial distribution of macular pigment, MP, in the human retina. The purpose of this work is a comparison of the two methods for a group of human volunteer subjects.
Resonance Raman imaging, RRI, is accomplished with a home-built instrument that uses 488 nm laser excitation and CCD camera based detection of Raman light backscattered from the MP molecules lutein and zeaxanthin. The Raman method detects the MP molecules directly and is highly molecule specific but it is influenced, in principle, by potential opacities of the human eye lens. For autofluorescence imaging, AFI, we use a home-built CCD camera based instrument that derives MP levels and distributions via two wavelength autofluorescence excitation spectrospopy. The AFI instrument detects retinal autofluorescence above ~700 nm and compensates for eye lens absorptions via signal normalization to the peripheral retina. Both instruments are capable of non-mydriatic measurements within a fraction of a second. For the comparison we recruited 20 volunteer subjects.
With both instruments we find distinctly differing MP distributions in different individuals, including distributions that are predominantly concentrated in the foveola, distributions that are spatially extended into the perifovea, and distributions with ring-shaped MP patterns. Differences in foveal MP levels are not due to differences in retinal layer thickness. In spite of the completely different spectroscopies involved, the MP distributions measured with both instruments for a given subject are remarkably similar. This includes the relative level of pigment concentration at given locations within the MP distribution, and spatial features such as ring diameters.
RRI and AFI are two objective optical methods suitable for the rapid screening of MP levels and their distributions in human subjects without need for pupil dilation. Both methods yield very similar results for the healthy human retina. The high molecule specificity of the Raman approach is not required in these cases. Therefore, AFI may have an advantage for healthy subjects in terms of simplicity and light exposure levels since AFI does not require expensive laser light sources. However, since Raman signals are not normalized to the retinal periphery, RRI could have an advantage in the detection of MP changes over time caused by nutritional supplementation or retinal pathologies.
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