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Naveen K. Yadav, Diana P. Ludlam, Kenneth J. Ciuffreda; Effect Of Binasal Occlusion (BNO) On The Visual-Evoked Potential (VEP) In Mild Traumatic Brain Injury (mTBI). Invest. Ophthalmol. Vis. Sci. 2012;53(14):4968.
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To assess the effect of binasal occluders (BNO) on the visually-evoked potential (VEP) amplitude and latency in visually-normal (VN) and in mild traumatic brain injury (mTBI) individuals. In clinical testing of the mTBI population, addition of the BNO to the spectacle lenses frequently reduces their symptom of abnormally-increased visual motion sensitivity (VMS).
Subjects were comprised of adult VN (n=10, mean age 26 years), and mTBI (n=10, mean age 28 years, 1-10 years post-insult) individuals typically with VMS. Conventional full-field VEP testing was employed (64 x 64 checkerboard pattern, 17º H x 15º V stimulus size, 85% contrast, 64 cd/meter square, 1 meter distance, average of 2 trials, binocular viewing with spectacle correction) under two conditions: without BNO, and with opaque BNO which occluded a 5.7º H x 15º V region of space 5.5º lateral to the edge of the test stimulus on either side. Subjective impressions while walking and attempting to grasp near objects were also assessed with and without BNO.
In the VN, the mean VEP amplitude decreased significantly (p ≤ 0.05) (21.60 ±3.72 µV to 17.37 ±3.03 µV) with the BNO in all subjects. In contrast, in the mTBI, the mean VEP amplitude increased significantly (p ≤ 0.05) (19.15 ±2.40 µV to 21.32 ±2.42 µV) with the BNO in all subjects. Latency (P100 ms) was normal and unaffected under all conditions and groups. Repeat testing in 3 subjects from each group revealed similar test-retest results. Visuomotor activities improved, with reduced symptoms (e.g., reduced nausea and decreased disorientation), with the BNO in the mTBI.
The results demonstrated significant, but opposite, directional effects on the VEP amplitude in the two groups. We speculate that mTBI patients habitually suppress visual information in the near retinal periphery to reduce their abnormal VMS. With addition of the BNO in mTBI, suppression is now rendered unnecessary. This leads to the spread of reduced inhibition 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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