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Naveen K Yadav, Kenneth J Ciuffreda; Effect of Binasal Occlusion and Base-In Prisms on the Visual-Evoked Potential (VEP) in the Visually-Normal and Mild Traumatic Brain Injury Populations. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3498.
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To assess the effect, and relative contribution, of binasal occlusion (BNO) and base-in prisms (BI) on the visually-evoked potential (VEP) amplitude and latency in the visually-normal (VN) and in the mild traumatic brain injury (mTBI) populations. Clinically, BNO, at times in conjunction with BI prisms, is added to the spectacle prescription of individuals with mTBI to reduce their abnormally-increased visual motion sensitivity (VMS).
Subjects were comprised of VN adults (n=20, mean age 25 years), and adults having mTBI (n=11, mean age 34 years, 1-10 years post-insult) and abnormally-increased VMS. There were 4 test conditions: 1) pattern VEP (64 x 64 checkerboard pattern, 17H x 15V degree field size, 1 Hz temporal frequency, 85% contrast, 74 cd/meter square, 20 second trial duration, 1 meter test distance, binocular viewing with spectacle correction), which served as the baseline comparison condition; 2) pattern VEP with BNO; 3) pattern VEP with 2 pd base-in (BI) prisms before each eye; and 4) pattern VEP with the combination of the above BNO and BI prisms, with the last 3 conditions counterbalanced. Four trials were averaged for each test condition. Figure 1.
In VN, the mean VEP amplitude decreased significantly (p<0.05) (~3 µV) with BNO in all subjects, as well as with the combination of BNO and BI prisms. There was no effect of BI prisms only. In contrast, in mTBI, the mean VEP amplitude increased significantly (p<0.05) (~3 µV) in all subjects with BNO only. In both groups, latency remained normal.
Only BNO alone demonstrated significant, but opposite, directional effects on the VEP amplitude, in both groups. Therefore, BNO alone can be used clinically for the objective differential diagnosis of suspected mTBI with VMS. We speculate that mTBI patients habitually attempt to suppress visual information in the near retinal periphery to reduce their abnormal VMS. With addition of the BNO in mTBI, the attempted motion suppression is now rendered unnecessary. This leads to the spread of reduced inhibition, thus producing enhanced central visual field responsivity. In contrast, in VN, it may reflect reduction of normal excitation over the same spatial regions, thus reducing central visual field responsivity.
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