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I. Alabboud, III, A. McNaught, D. Mordant, A. R. Harvey; Quantitative Spectral Imaging of the Retina. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2581.
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Hyperspectral imaging of the retina presents a unique opportunity for direct and quantitative mapping of retinal biochemistry - particularly of the vasculature where blood oxymetry is enabled by the strong change of absorption spectra with oxygenation. This is particularly pertinent both to research and to clinical investigation and diagnosis of retinal diseases such as diabetes, glaucoma and age-related macular degeneration. The optimal exploitation of hyperspectral imaging however, presents a set of challenging problems, including; the effects of optical clutter and poorly characterised and controlled optical environment of the retina; the erratic motion of the eye ball; and the compounding effects of the optical sensitivity of the retina and the low numerical aperture of the eye.
We have developed a spectral retinal imaging system and data processing techniques that address these issues: it is based on a conventional fundus camera into which a liquid crystal tuneable filter has been integrated so as to spectrally filter the illumination. We report the development of an automated, calibration-free process and associated algorithms for the quantification of retinal blood vessel oxygenation. The algorithms are based on a physical model for light propagation through the vasculature that includes the best-fit calculation of a range of vascular parameters that includes blood oxygenation.
This technique has enabled oxymetry maps to be rapidly calculated for a comprehensive fraction of the retinal vasculature. Random variations in oxygenation along a blood vessel of assumed constant oxygenation are typically less than 4%. Quantitative examples of retinal blood oxymetry will be presented for healthy and diseased retinas.
Hyperspectral imaging is capable of accurately producing quantitative oximetric map of the retina and monitoring its response to treatment. This holds promise for its application in clinical investigation and diagnosis of retinal diseases.
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