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X.-R. Huang, R. W. Knighton, L. N. Cavuoto; Damage to Distribution of the Retinal Nerve Fiber Layer in a Rat Model of Glaucoma. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3345.
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The retinal nerve fiber layer (RNFL), which consists of axons of retinal ganglion cells, is damaged in glaucoma. Actin filaments (AF), a major component of the cytoskeleton, provide mechanical support for the axons. We used phalloidin labeling of F-actin to study structural changes of the RNFL during the development of glaucoma in a rat model.
Experimental glaucoma was induced in the left eyes of Wistar rats by translimbal laser photocoagulation (532nm diode laser, 500mW power, 0.5 second duration, 50µm diameter spot size). The intraocular pressure (IOP) in both eyes was measured before and after treatment. After the IOP of treated eyes was elevated at least 6 mmHg higher than the control and maintained for at least 2 weeks, the retina was isolated free from the pigment epithelium and stained with phalloidin to label F-actin and DAPI fluorescence to counterstain ganglion cell bodies. The flat-mounted retina was examined by confocal laser scanning microscopy. Both en-face images and cross-sectional images of the RNFL were taken. Retinal regions around the optical nerve head (ONH) and at different eccentricities were examined.
In the en-face image of the normal retinas, nerve fiber bundles identified by phalloidin labeled F-actin appeared as bright stripes. The cross-sectional images showed that the bundles were uniformly stained and the RNFL was separated from deeper layers by a layer of ganglion cells. For the treated retinas, RNFL damage was most frequently found in the dorsal retina. In some cases the damage appeared to start near the ONH and propagate along the bundles to the peripheral RNFL. Different degrees of RNFL damage were observed in cross-sectional images: 1) the staining of the bundles became less uniform than that of normal bundles; 2) the RNFL thickness was reduced; or 3) the bundles totally disappeared.
Elevation of IOP causes non-uniform damage to the RNFL as revealed by phalloidin staining of the actin cytoskeleton. The damage usually occurs first in the dorsal retina. The degree of damage varies from distortions of the AF staining to the total disappearance of the RNFL.
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