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V. Diaconu, C. Boisjoly, P. Forcier; Optic Nerve Oxygenation Assessed By Multichannel Spectroreflectometry. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2272.
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© ARVO (1962-2015); The Authors (2016-present)
The goal of this study was to explore the human optic nerve head (ONH) capillaries by the multichannel spectroreflectometry technique, to derive the relative oxyhemoglobin, hemoglobin and capillary blood content as a function of intra ocular pressure (IOP). We compared the effect of oxyhemoglobin change as a function of perfusion pressure in the eye and in a peripheral system, (eg the end of the finger tip when the pressure was applied on the arm). A comparison between these two structures would tell us whether the mechanisms involved in the link between perfusion pressure, oxygenation and blood content are similar throughout the vascular system.
The full spectrum reflectometry measurements were performed with a slightly modified version of the "On line Spectroreflectometry Oxygenation Measurement in the Eye" instrument (OSOME Faubert & Diaconu US Patent # 5,919,132). Based on a model of optical reflectance and absorbance of different biological layers it is possible to derive the relative oxyhemoglobin, hemoglobin and blood content in optic disc capillary and on the finger tip as a function of IOP and arm pressure respectively. Nine young subjects between 19 and 24 years old participated in the experiment. In the first session for each subject was calibrated the IOP according to then pressure applied on the sclera by means of a suction cap. The spectral reflection was then measured on line from the ONH of every subject for two consecutive sessions of ascending and descending sucked pressure varied along a continuum between 0 and 60mm Hg. In the second experiment the spectral reflection was recorded on line from the finger tip for two consecutive ascending and descending sessions of the pressure applied on the arm which varied along a continuum from 0 to 140mmHg in conditions that: a) the arm is vertically positioned above the head. b) the arm is vertically positioned downward.
The results demonstrate a resemblance between the data that describe the blood oxygen variation in the ONH and on the finger tip when the arm is vertically positioned above the head. Both systems seem to present regularization for the blood oxygen content when small (30mmHg) pressure perfusion was applied. However the phenomenon of oxygen content regularization is not present on the finger tip when the arm is vertically positioned downward.
The auto regulation of blood oxygen content on the ONH demonstrated by Ernest (1963) may not be a unique property of the ONH but also may apply to a given vascular system which is positioned higher then the cardiac pump.
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