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J. C. Ramella-Roman, P. Lemaillet, D. Duncan, M. Ibrahim, Q. Nguyen; Imaging System for Oxygen Saturation and Blood Flow Measurement in the Retina. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5964.
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Measurements of oxygen saturation and flow in retinal vessels have proven to be an important factor in monitoring diabetic retinopathy (DR). Measurement of retinal oximetry can be complicated due to saccadic eye movements, a difficulty that can be circumvented with spectroscopic snapshot imaging. Oxygen saturation (SO2) measurements in the eye rely on the hemoglobin absorbance spectrum to calculate the oxygen content. Flow measurements can be achieved by following the motion of red blood cells in retinal vessels.
We present a retinal imaging system based on a commercially available fundus ophthalmoscope capable of measuring both blood flow and oxygen saturation in the retina. The velocimetry component of the setup uses a green illumination and a fast acquisition camera to track red blood cells. The oxygen saturation measurement portion is composed of a lenslet array combined with a filter array that projects nine wavelength-sensitive sub-images on a large format CCD (please write out when used for the first time). Calibration of the flow measurement employs an eye phantom with micro-tube mimicking the vessel, with controlled input blood flow, whereas calibration of the oxygen saturation aspect of the setup relies on a set of epoxy phantoms mimicking the optical properties of the retina.
Quantitative assessment of oxygen saturation and velocity measurements are demonstrated in vitro and in vivo. Oxygen maps built with our system can determine not only values of SO2 on the retinal vessels but also in the surrounding choroidal area. The nine wavelength system results are compared with a higher resolution two-wavelengths system.
The combined oximeter and flow system is capable of quantifying oxygenation and red blood cells velocity in retinal vessels. The system that has been developed could be an important tool in the assessment of early stages of DR , which may affect approaches to management.
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