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Xiang-Run Huang, Ye Zhou, Wei Kong, Robert W. Knighton; Change of Retinal Nerve Fiber Layer Reflectance Correlated with Cytostructural Change in Glaucoma. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2442.
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Reflectance of retinal nerve fiber layer (RNFL) arises from light scattering by cylindrical structures in axons. Change of RNFL reflectance, therefore, indicates change of axonal cytostructure. We have shown that 1) glaucomatous damage alters axonal cytostructure and 2) at early stages of damage RNFL reflectance decreased before thinning of the RNFL. In this study, we investigated the relation between changes of the RNFL reflectance and axonal cytostructure at different stages of glaucomatous damage.
High intraocular pressure (IOP) was induced in the left eyes of rats by laser photocoagulation of trabecular meshwork. The RNFL reflectance spectrum from 400 - 830 nm was measured in an isolated retina. After reflectance measurements, the retina was stained with antibodies to label the axonal cytoskeleton. Cytoskeletal change in treated retinas was graded as normal-looking bundles (1), structural distortion (2) and apparent loss of cytostructure (3). Reflectance spectra were calculated for bundles located in these regions. Mean reflectance (R) in short, medium and long wavelength ranges was calculated and the ratios of short to medium (MS) and long to medium (ML) of reflectances were used to evaluate spectral changes. Spectra were also fitted with a two-mechanism scattering model to predict the proportion of thin and thick cylindrical structures that contribute to the RNFL reflectance.
Fifty-two bundles of 30 control retinas (OD) and 131 bundles of 41 treated retinas (OS) were examined. For Group 1, both MS and ML were similar to control (Table). For Group 2 and 3, MS was significantly lower than the normal. ML of Group 3, however, was higher than that of the control. The spectral fitting showed that the number of thin cylinders significantly decreased in Group 2 and 3 (p<0.001).
Elevation of IOP causes change in the RNFL reflectance spectrum. The change may occur first at short wavelengths. Change in the RNFL reflectance spectrum correlates with change of axonal cytostructure.
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