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Vanessa Fimreite, Naveen K Yadav, Kenneth J Ciuffreda; Effect of Luminance on the Visual Evoked Potential (VEP) in Visually-Normal and Mild Traumatic Brain Injury (mTBI) Populations. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3497.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the effect of luminance on VEP amplitude and latency in the visually-normal (VN) and in the mild traumatic brain injury (mTBI) adult populations; the findings are equivocal in the former, and have never been tested in the latter, populations.
VN individuals (n=20, mean = 23 years) and those with mTBI (n=12, mean = 27 years; 2 months to 10 years post-injury) were tested. Pattern VEP testing was employed using the DIOPSYSTM NOVA-TR system (17 H x 15 V degree field size, 20' check size, 74 cd/m2 luminance, 1 Hz temporal frequency, 20 second trials, 1 meter distance, binocular viewing with spectacle correction), which served as the baseline condition. Luminance levels were then reduced with five different neutral density filters (ND) (0.5, 1.0, 1.5, 2.0, and 2.5), presented in a counterbalanced manner, with all compared to baseline. Luminance levels were reduced to 23.6, 7.4, 2.2, 0.5, and 0.2 cd/m2, respectively, with the ND filters. Four trials were averaged for each test condition.
In both groups, the mean VEP amplitude significantly reduced beyond 2.2 cd/m2 (1.5 ND) (p<0.05). At each luminance level, the mean VEP amplitude was significantly lower in mTBI than in VN (p<0.05). In contrast, in both groups, the mean VEP latency increased progressively and significantly with luminance decrease (p<0.05). At each luminance level, however the mean VEP latency was significantly higher in mTBI than in VN (p<0.05). Mean latency variability was significantly higher (~30-300%) in mTBI than in VN (p<0.05).
The VEP amplitude was robust to large reductions in luminance in both groups. In contrast, the VEP latency was more sensitive to luminance reduction in both groups. However, the differential latency increase and its related increased variability with luminance reduction, in the mTBI population as compared to VN, suggests a magnocellular pathway deficit, perhaps reflecting increased neural noise consequent to the brain injury.
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