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W. H. Ridder, III, A. Tong; Sweep Visual Evoked Potential (sVEP) Acuity Extrapolation Techniques. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5884.
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© ARVO (1962-2015); The Authors (2016-present)
sVEPs are generally used to rapidly obtain visual acuity. The most common method of determining visual acuity with sVEPs is to employ a linear regression on the high spatial frequency data and extrapolate this line to the X-axis. A recent study (Zhou et al., 2008) has suggested that by plotting the data as response amplitude vs the log of stimulus visual angle (later referred to as logVA) instead of against the stimulus spatial frequency in cycles per degree (later referred to as CPD), yields a more accurate measure of visual acuity. The aim of this study was to make a direct comparison between these two methods.
Ten normal subjects took part in this project. Stimulus production and data analysis was done with an Enfant 4010. Standard VEP recording techniques were employed. The stimulus was a horizontal-oriented, sine wave grating. Sweeps were repeated until the confidence intervals for the data were no longer decreasing. The response amplitude of the VEP was plotted against 1. the CPD or 2. the logVA. A line was fit to the high spatial frequency data and extrapolated to an amplitude of zero microvolts to determine the visual acuity. The Bailey Lovie logMAR chart was used to determine visual acuity.
The average logMAR acuity for all of the subjects was -0.06 ± 0.070 (SD). The average sVEP acuity estimates were -0.01 ± 0.134 and -0.14 ± 0.243 with the CPD and logVA techniques, respectively. Paired t-tests demonstrated that both the CPD (p = 0.29) and logVA (p = 0.27) techniques were equally good at predicting Bailey Lovie logMAR acuity. The average difference between the logMAR acuity and the CPD and logVA extrapolated acuities were -0.05 ± 0.139 and 0.09 ± 0.239, respectively. A paired t-test between the CPD and logVA data indicates that the logVA technique resulted in higher visual acuity estimates (p = 0.01).
Since both the logVA and CPD techniques of extrapolating visual acuity from the sVEP are not significantly different from the Bailey Lovie logMAR acuity, either technique can be used to determine acuity.
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