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Xiang-Run Huang, Ye Spector, Jianzhong Qiao; Does Axonal F-actin Contribute to Retinal Nerve Fiber Layer Reflectance?. Invest. Ophthalmol. Vis. Sci. 2016;57(12):879.
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© ARVO (1962-2015); The Authors (2016-present)
Clinical assessment of the retinal nerve fiber layer (RNFL) using optical methods relies on measurements of RNFL optical properties, such as reflectance and birefringence. Identifying anatomic bases that underlie these optical properties will improve the interpretation of the assessment. Cylindrical structures in ganglion cell axons are known to contribute to RNFL reflectance. In rodent retinas, axonal microtubules contribute about one half of RNFL reflectance. This study was conducted to evaluate axonal F-actin’s contribution to RNFL reflectance in rodent retinas by using an F-actin depolymerizing agent Cytochalasin D (CD).
Rat retina, isolated free from the pigment epithelium, was measured by means of imaging reflectometry. An experiment consisted of baseline and treatment periods. During baseline, the tissue was perfused with a physiological solution. During the treatment period (60 – 100 min), the solution was switched either to a control solution or a similar solution with 0.3 μM CD. Reflectance images of the retina were taken regularly at 500 nm. Images were also taken at 17 wavelengths between 400 nm and 830 nm over the time course. A background removal algorithm was used to evaluate RNFL reflectance. The temporal change of the reflectance after solution switch was used to evaluate the contribution of F-actin to the RNFL reflectance. After optical measurements, the tissue was fixed for structural evaluation using immunohistological staining and confocal imaging.
Five and seven retinas were used for control and treatment experiments, respectively. In control experiments, F-actin strands were visible within bundles (Fig. A); the reflectance of nerve fiber bundles was approximately stable, declining 2% - 7%. In treated retinas, however, confocal images of F-actin stain showed no apparent F-actin strands running along bundles (Fig. B). The reflectance of the corresponding bundles declined 4% – 17% at 500 nm (Fig. C). The reflectance change was similar at all wavelengths examined.
The effect of 0.3 μM CD suggests that disruption of F-actin strands within bundles resulted in less than 17% decrease of the RNFL reflectance.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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