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P. Sauvageau, V. Diaconu; Stationary Retinal Light Illumination Induces Changes in Optic Nerve Head Blood Content. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2091.
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It is generally accepted that an autoregulation process of blood flow takes place in the optic nerve head in order to keep the local blood flow constant. It is important to note that the presence of this process does not regulate the blood flow in a tissue at all times. Many previous studies have tried to determine the limits of the autoregulation process in order to prematurely detect abnormalities of the retinal vascular system which is the cause of numerous eye diseases. The purpose of the present study was to record, continuously and in real time, changes regarding both the blood flow and the concentration of oxygen in the optic nerve head capillaries during stationary and uniform retinal illumination using a new technique of multichannel spectroreflectometry.
7 subjects in good health (4 females, 3 males) aged between 20 and 28 participated in this experiment. The relative blood optical density at the optic nerve head (RBODonh) and the relative oxygen concentration at the optic nerve head (ROConh) were recorded online by full spectrum reflectometry (430 - 650nm) using a 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, the oxyhemoglobin and hemoglobin optical densities of the optic nerve head capillaries were computed during 300 seconds with a white retinal illumination light at 60 degrees.
The results demonstrate that stationary and uniform retinal illumination induced changes in both the RBODonh and the ROConh. All subjects showed an instantaneous and constant decrease in optical reflectivity associated with a constant increase of RBODonh and ROConh. These increases could last, depending on the subject, between 30 to 60 s. Thereafter, a constant reduction of RBODonh and ROConh, equivalent to the previous increase, was observed. This thus permitted the RBODonh and the ROConh to return to normal and stable values with a plateau state at 60 to 120 s after the beginning of the stimulation.
By using a multichannel spectroreflectometry technique, it is possible to detect changes in the blood content of the optic nerve head capillaries during a stationary and uniform retinal illumination. This finding can be important in order to establish early vascular deficiencies in the retina.
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