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Daniel Shedd, Brittany Coats, Developmental Head Injury Biomechanics Laboratory; Visual Dysfunction Following Low Level Blast Exposure in Rats. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4799.
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© ARVO (1962-2015); The Authors (2016-present)
Blast exposure is a leading cause of eye injury for the US Army. Closed globe trauma may not be detected right away, and little is known about the time course of visual dysfunction following blast exposure. To better understand the mechanisms behind blast induced vision loss, a rodent model was developed and used to characterize the time-dependent changes in visual acuity after blast exposure using behavioral vision testing and optical coherence tomography (OCT).
Anesthetized Long-Evans rats (300-350g, n=26) were exposed to 230 kPa pressure waves using a 6 inch diameter compressed-air blast tube. Animals were evaluated at 1 day post-blast and weekly up to 8 weeks post-blast. A custom vision behavior device was built to measure the visual acuity threshold using the optokinetic nystagmus reflex. Test animals were placed in the center of the device and a cylindrical sine wave grating was displayed on four surrounding computer monitors. The grating rotated around the animal, which caused the animal to reflexively track the grating motion. The contrast of the grating at which the direction of drift was tracked by the animal represented the level of functional visual acuity. Three trials were completed for each animal at each time point. A two-tailed matched-pair test with p=.05 was used to find significant vision changes. OCT imaging (Bioptigen Envisu™ R2200) with an ultra-high resolution (UHR) light source was used to identify changes in retinal thickness in 8 regions around the optic nerve.
There was a significant reduction in visual acuity in all rats 1 day after blast exposure (Figure 1). This reduction was sustained for the duration of the study. The visual acuity in control animals (n=26) increased after day one and remained stable up to 8 weeks. Retinal thickness was normalized to baseline values and compared with controls. Several regions of the posterior retina thickened slightly (~8%) at week 2, but was resolved by week 8.
Low level blast exposure results in an acute decrease in visual function that was sustained up to 8 weeks. The blast also resulted in delayed changes in retinal thickness which resolved over a month. Additional studies are underway to evaluate the electrical physiology of the retina to support theh findings of decreased functional visual acuity.
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