Retinal oximeter for the blue-green oximetry technique

Abstract

Abstract. Retinal oximetry offers potential for noninvasive assessment of central venous oxyhemoglobin saturation (SO 2 ) 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 bluegreen 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 SO 2 measurements of ∼1 and ∼65%, respectively. These saturations, calculated using the calibration line from earlier work, are internally consistent with a standard error of the mean of ± 2% SO 2 . 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).

Retinal Vessel Oxygen Saturation in Healthy Individuals

“…Crittin et al used similar optical approach in developing their two-wavelength oximetry system, 9 while Hammer et al developed an oximetry instrument that also captured two fundus images simultaneously with two wavelengths of light, but with a different optical approach. 10 Other groups using diverse approaches also have contributed to the field of retinal oximetry, such as Denninghoff et al, who developed a multiwavelength oximetry system, 11,12 Ramella-Roman et al who introduced a multiaperture camera system for retinal oxygen saturation measurement, 13 Kagemann et al who used Fourier domain optical coherence tomography to assess spectral oximetry, 14 Li et al who used an adaptive optics confocal scanning laser ophthalmoscope to measure oxygen saturation in small retinal vessels, 15 Khoobehi et al who developed a hyperspectral system that has been used mainly for oxygen saturation measurements of optic nerve heads in monkeys, 16,17 Harvey et al who developed a hyperspectral instrument for measuring retinal oxygen saturation in vivo and in a model eye, [18][19][20] and Humayun's group who developed different hyperspectral system for measuring oxygen saturation within retinal vessels. 21,22 For review see the report of Harris et al 23 Modern spectrophotometric retinal oximetry takes advantage of the great development of digital cameras and computer technology that has taken place in the last few decades.…”

Accuracy of retinal oximetry: a Monte Carlo investigation

“…Despite the efforts to develop and improve retinal oximetry, many limitations still exist. 7 The accuracy of retinal oximetry is affected by factors such as variations in vessel size 15 and pigmentation, 6 multiple light paths 16,17 and vessel wall thickness, 7 and others. Variations in vessel size and pigmentation are considered to have a major impact on the accuracy of sO 2 measurement.…”

Retinal Oximetry With a Scanning Laser Ophthalmoscope

“…Oxygen saturation was found to be 101% to 102% and 65% in the retinal arteries and veins, respectively, suggesting that the EOX is sensitive to retinal oxygen saturation. In 2011, Denninghoff et al 14 reported on the use of a new modified confocal SLO (ROx-3) for blue-green oximetry in both swine and human subjects. Results on retinal oxygen saturation were in the same range as reported by other research groups.…”