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B. Khoobehi, J. Beach, H. Kawano, H.W. Thompson, J. Ning; Evaluation of Relative Oxygen Saturation of Optic Nerve Head (ONH) Tissues in an Acute–Elevated–IOP Model in the Non–human Primate Using Hyperspectral Imaging . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2295.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To use reflectance hyperspectral imaging to evaluate the stimulus relationship between IOP perturbations and oxygen saturation in ONH tissues and retinal artery/vein pairs in normal primate eyes. Methods: Two cynomolgus monkeys were used. To monitor and raise IOP, a 27–guage needle was connected to a bottle of BSS and inserted into the anterior chamber. For each eye, IOP was elevated through a range of IOPs (10, 20, 30, and 45 mm Hg). Spectral information was obtained 10 and 30 minutes after each elevation using a hyperspectral imaging system that viewed the ONH through a fundus camera; three images were obtained at each time point. Each eye was imaged twice, a week apart. Oxygen–dependent changes in hemoglobin reflectance spectra were evaluated from the ONH and overlying retinal vessels. A relative saturation index (RSI), derived from amplitudes of oxy– and deoxyhemoglobin spectra, was employed to map relative saturation over the ONH and vessels, and to follow relative saturation changes resulting from changes in IOP. Factorial analysis of variance was used to detect variability between animals, eyes, days, location, bands, IOPs, and post IOP elevation conditions, with post–hoc testing using protected t–tests with alpha levels adjusted for multiple comparisons using a simulation method. Variance components analysis was used to compare the variances of changes in RSI at each location (retinal artery and vein on the ONH, temporal and nasal area of the ONH, excluding the cup) at different IOPs. Results: The RSI was significantly (p < 0.05) reduced in the retinal artery and vein at IOPs of 30 mmHg and 45 mmHg, respectively. Smaller but not significant reductions were found between 20 and 30 mmHg. No detectable differences were seen between 10 and 20 mmHg. The RSI was significantly reduced in the nasal ONH at an IOP of 45 mmHg; the RSI in the temporal ONH was reduced, but not significantly, at this IOP. At lower IOPs, differences in RSI were not seen in the ONH. At a given IOP, responses from different subjects and responses from the same subject on different days were not significantly different. Conclusions: In retinal vessels, an autoregulatory function is present below 20 mmHg. This function begins to be impaired at IOPs between 20 and 30 mmHg, and is severely impaired at 45 mmHg. In the ONH, the autoregulatory function is preserved up to 30 mmHg. Hyperspectral imaging is capable of monitoring the oxygen saturation response of retinal/ONH structures in a primate model of glaucoma.
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