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Kevin Willeford, Naveen Yadav, Kenneth Ciuffreda; Effect of Test Duration on the Visual-Evoked Potential (VEP) and Alpha Wave Responses. Invest. Ophthalmol. Vis. Sci. 2013;54(15):6143.
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The visual-evoked potential (VEP) and a subcomponent, the attentionally-related alpha wave, are often not included in clinical vision testing due to claims of having high variability (i.e., poor repeatability). There is no standardized test duration for either electrophysiological phenomenon, which may be a cause of the posited variability. Thus, the purpose of this study was to assess the effect of test duration on the visual-evoked potential and alpha responses.
16 visually-normal, young-adult subjects (ages 22 to 25 years) participated in the experiment. The DiopsysTM NOVA-TR system was used to obtain the visual-evoked potential (VEP) amplitude and latency measurements, as well as the alpha-wave with its power spectrum (8-13 Hz). Four different test durations were used in a counterbalanced manner: 10, 20, 45, and 60 seconds. Two test conditions were used: (1) eyes open, to obtain the VEP and alpha wave responses, and (2) eyes closed, to obtain the maximum alpha wave response. The stimulus for the binocular eyes-open condition consisted of a black-and-white, alternating checkerboard pattern (17° H x 15° V, 64 cd/m2, 85% contrast, 1 Hz temporal frequency) tested at 1 meter with full refractive correction. Five trials were performed for each of the 8 conditions during one session.
Regarding the VEP parameters, only variability [i.e., coefficient of variation (CV)] of the VEP amplitude changed significantly with test duration (p < 0.0001): it decreased with increasing test duration (group mean CV=0.195 for 10 seconds to 0.098 for 60 seconds). The 45 and 60 second trials showed similarly low variability (group mean CV= 0.096 and 0.098, respectively). Mean amplitude and latency did not change. Regarding the alpha responses, test duration did not have a significant effect on either the mean alpha power or its variability (p > 0.05)
The findings demonstrate that a 45 second test duration is sufficient to minimize variability of the VEP amplitude measurements, whereas a 10 second test durations is sufficient for accurate measurement of the alpha wave. Optimization of test duration allows for repeatable measures with less total test time. This is especially important for special clinical populations (e.g., ADHD), where short test sessions are critical to obtain repeatable, valid measures.
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