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Xiang-Run Huang, Ye Zhou, Siobhan Williams, XiaoPeng Zhao, Robert W. Knighton; Does Reflectance Speckle of Retinal Nerve Fiber Layer Relate to Axonal Activity?. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1746.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal nerve fiber layer (RNFL) consists of axons of retinal ganglion cells. In high resolution images, RNFL reflectance shows a speckled texture. Change of the speckle pattern with time suggests temporal change of the scattering structures. Neuronal axons are dynamic structures; their contents move continuously with axonal transport. In this study, we tested the hypothesis that temporal change of RNFL speckle is associated with axonal dynamic activity.
Isolated rat retinas were perfused in a warm oxygenated physiologic solution. A series of reflectance images were collected every five seconds by an imaging reflectometer. Areas were defined on bundles to sample reflectance speckles (box in Fig. A). The temporal change of speckle was described by the time course of correlation between speckle patterns, that is, the correlation was calculated between the first image and each consecutive image in the image series. The time course was then fitted with an exponential function, the time constant of which was used as a measure of the dynamic change of speckle. Change of RNFL speckle was measured in normal living retinas, retinas fixed with paraformaldehyde and retinas with microtubules depolymerized by colchicine.
In living retinas, the speckled texture of RNFL reflectance changed over time. The correlation decreased rapidly at the beginning and then flattened (Fig. B). In fixed retinas, the speckled texture of nerve fiber bundles was stationary with high correlation between images. In retinas with depolymerized microtubules, the decrease of correlation was slower than that of normal living retinas (Fig. C), suggesting slower axonal activity.
Temporal change of RNFL reflectance speckle is associated with axonal dynamic activity. Measurement of RNFL speckle change may provide a new means to detect axonal degeneration.
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