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Alistair J. Barber, Melissa A. Bridi, Wade A. Edris, Sumathi Shanmugam, Cheng-Mao Lin, David A. Antonetti, Steven F. Abcouwer; Comparison Of Electrophysiological And Optokinetic Measures Of Visual Function After Retinal Ischemia In Brown-norway Rats. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2447.
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The aim of this project was to compare the effect of mild retinal ischemia reperfusion (IR) injury on the electroretinogram (ERG) and optokinetic measures of visual function in Brown-Norway rats. Both approaches can been used to assess visual function in animals but their comparative sensitivities to retinal ischemia have not been studied.
Male Brown-Norway rats were subjected to retinal IR in one eye by raising the intraocular pressure to 110 mmHg for 45 min using a needle placed into the anterior chamber, connected to a syringe pump with sterile saline. The opposing eye was used as a sham control. At various times following reperfusion, the effects of IR on cell death and plexiform layer loss were determined by evaluating DNA fragmentation (TUNEL and Cell Death ELISA™) and retinal-layer thinning (H&E). To evaluate the effects on retinal function, ERG responses (Espion2, Diagnosys) were quantified and spatial frequency and contrast sensitivity thresholds were measured by optokinetics (Optomotry™, Cerebral Mechanics).
TUNEL analysis and cell death ELISA confirmed a significant increase in neuronal apoptosis in the IR retinas compared to opposing sham control (p<0.05). The ratio of thickness of the inner plexiform to outer plexiform layers was significantly reduced by IR (p<0.01). ERG recordings yielded the classic wave forms with intact a-, b- and oscillatory potential components, with the amplitude of the b-wave significantly reduced by IR (55% of control, p<0.002). IR also significantly reduced the spatial frequency threshold (48% of control, p<0.001), but almost completely abolished the contrast sensitivity response (6% of control, p<0.0015).
The results demonstrate that the optokinetic contrast sensitivity response is much more affected by ischemic damage than the spatial frequency threshold or ERG b-wave amplitude. These data suggest that the greatest impact of IR is on the inner retina, responsible for contrast sensitivity, and that there is a lesser impact on the other parts of the retina responsible for the ERG b-wave and spatial frequency threshold. The relative differences in sensitivity of these measurements of visual function may be useful in identifying layer-specific retinal pathology in animal models of degenerative retinal diseases.
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