Retinal oximeter for the blue-green oximetry technique

Retinal oximetry offers potential for noninvasive assessment of central venous oxyhemoglobin saturation (SO2) via the retinal vessels but requires a calibrated accuracy of +/- 3% saturation in order to be clinically useful. Prior oximeter designs have been hampered by poor saturation calibration accuracy. We demonstrate that the blue-green oximetry (BGO) technique can provide accuracy within +/- 3% in swine when multiply scattered light from blood within a retinal vessel is isolated. A noninvasive on-axis scanning retinal oximeter (ROx-3) is constructed that generates a multiwavelength image in the range required for BGO. A field stop in the detection pathway is used in conjunction with an anticonfocal bisecting wire to remove specular vessel reflections and isolate multiply backscattered light from the blood column within a retinal vessel. This design is tested on an enucleated swine eye vessel and a retinal vein in a human volunteer with retinal SO2 measurements of similar to 1 and similar to 65%, respectively. These saturations, calculated using the calibration line from earlier work, are internally consistent with a standard error of the mean of +/- 2% SO2. The absolute measures are well within the expected saturation range for the site (-1 and 63%). This is the first demonstration of noninvasive on-axis BGO retinal oximetry. (C) 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.3638134]