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X.–R. Huang, R.W. Knighton; Microtubules Contribute to the Birefringence of Retinal Nerve Fiber Layer . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2511.
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The retinal nerve fiber layer (RNFL) exhibits birefringence due to the oriented cylindrical structure of ganglion cell axons. Possible birefringent structures include axonal membranes, microtubules, and neurofilaments. A significant contribution from microtubules is generally assumed, but has not been demonstrated. This study used the microtubule depolymerizing agent colchicine to evaluate the contribution of microtubules to RNFL birefringence.
Rat retina, isolated free from the pigment epithelium, was measured in transmission at 500 nm by means of imaging polarimetry. Retinal nerve fiber bundles were oriented at approximately 45° with respect to two crossed polarizers. Images were taken over an extended period. During baseline, the tissue was perfused with a physiological solution. During a treatment period, the solution was switched either to a control solution identical to the baseline solution or a similar solution containing colchicine. The contrast of nerve fiber bundles was calculated to evaluate change of RNFL birefringence over time.
Viewed between two crossed polarizers, birefringent retinal nerve fiber bundles appeared as bright stripes. The contrast of nerve fiber bundles was stable in control experiments (triangles in Figure). However, in treatment experiments bundles were bright during the baseline period but the contrast of bundles decreased rapidly when the colchicine solution was applied (circles in Figure). After 30 min of treatment bundles were barely visible.
Microtubules make a significant contribution to the RNFL birefringence.
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