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Naveen Yadav, Kenneth Ciuffreda; Optimization of Check Size and Contrast on the Visual-Evoked Potential (VEP) in Visually-Normal Individuals. Invest. Ophthalmol. Vis. Sci. 2013;54(15):6140.
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The literature results are equivocal regarding the effect of check size (CS) and contrast (C) on the amplitude and latency of the visually-evoked potential (VEP) in the visually-normal (VN) adult population. Thus, the purpose of this study was to assess the effect of these two parameters on the VEP response in this population to develop optimized test parameters.
Subjects were comprised of VN adults (n=20, mean age 27 years, 8 male and 12 female). Conventional full-field VEP testing was employed using the DIOPSYS NOVA-TR system (17 H x 15 V degrees stimulus size, 64 cd/square meter, 1 Hz temporal frequency, 1 meter distance, binocular viewing with spectacle correction) with three different CSs (10', 20', and 40') and at two C levels (20 and 85%). The average of four trials for each of the 6 test conditions was used in the analysis. All 6 test conditions were counterbalanced. Test duration was 20 seconds for each trial.
A two-way, repeated-measures ANOVA was performed for the two stimulus parameters. There was a significant effect of CS (p ≤ 0.05) and C (p ≤ 0.05) on the VEP amplitude. The 20' CS produced the greatest amplitude at both contrast levels (i.e., at 20% = 10.98 µV and 85% = 19.85 µV), which were significantly different (p ≤ 0.05). Similarly, there was a significant effect of CS (p ≤ 0.05) and C (p ≤ 0.05) on VEP latency (P100 ms). The 40' CS produced the consistently shortest latency at both C levels ((i.e., at 20% = 104 ms and 85% = 103 ms), which were not significantly different (p ≥ 0.05).
At both C levels, use of the 20' CS would be optimal for amplitude-sensitive conditions, such as amblyopia and macular degeneration, in which reduced amplitude would be expected at both contrast levels, which likely reflects a parvocellular deficit. In contrast, the 40' CS would be optimal for latency-sensitive conditions, such as glaucoma, in which a larger low contrast stimulus would result in delayed and abnormal latency, which likely reflects a magnocellular deficit. The present findings are consistent with psychophysical and neurophysiological findings with respect to high and low spatial frequency and contrast processes of the dual visual systems.
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