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H. Kawano, J. Beach, J. Ning, M. Lanoue, B. Khoobehi; Measurement of Oxyhemoglobin Saturation in the Optic Nerve Head and Retinal Vessels Using Hyperspectral Image Analysis . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2587.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To use a reflectance hyperspectral image technique to evaluate the oxyhemoglobin saturation of the optic nerve head (ONH) and overlying retinal vessels in monkeys under conditions of perturbed oxy–deoxyhemoglobin content resulting from breathing room air or pure oxygen. Methods: The hyperspectral images of the ONH and overlying retinal vessels in the eyes of cynomolgus monkeys were obtained using a fundus camera with an imaging spectrograph coupled to a CCD camera. Two conditions were observed: breathing room air (2 time points) and 100% oxygen (5 time points). Reflectance spectra were evaluated for changes in the amplitudes of the absorption bands known for oxy– and deoxyhemoglobin, using isosbestic wavelengths to separate the bands. Relative oxyhemoglobin saturation of the retinal artery and vein on the ONH and temporal and nasal area of the ONH, excluding the cup, was assessed from changes in reflectance spectra. This analysis was applied to produce pixel maps of saturation changes on the ONH and to evaluate saturation changes averaged from vessels and across regions of the ONH. Results: Under room air (RA) conditions, the oxyhemoglobin spectrum was present in retinal vessels (RSIartery–RA = 0.261 ± 0.007, RSIvein–RA = 0.159 ± 0.001) and in the ONH responses (RSItemporal–RA = 0.137 ± 0.007, RSInasal–RA = 0.142 ± 0.013). Pure oxygen (O2) markedly increased oxygen saturation in veins (RSIvein–O2 = 0.256 ± 0.009); increases in arteries (RSIartery–O2 = 0.312 ± 0.002) and the ONH (RSItemporal–O2 = 0.151 ± 0.004, RSInasal–O2 = 0.180 ± 0.007) were smaller. Saturation maps showed increases in both arteries and veins, and distinctly demonstrated the saturation changes in the ONH. Conclusions: Relative increases in blood oxygen saturation in retinal vessels and the ONH were detected by hyperspectral imaging. Breathing pure oxygen increased the venous saturation to levels comparable with arterial saturation during normal room air breathing. Smaller changes in oxygen saturation in the ONH may indicate a more active autoregulatory function in this tissue.
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