To compare contrast sensitivity with transient visual evoked potential (VEP) and Freiburg (Fr) psychophysical test in normal adults.

33 emetropic volunteers aged 18 - 28, mean ± SD 21.7 ± 0.4 and corrected visual acuity of 20/20 or better, participated in this study. In Fr test, the contrast thresholds were obtained at spatial frequencies (SFs) of 1 and 5 cycles per degree and then logarithmic units of contrast sensitivity were calculated based on the obtained contrast thresholds. The amplitude and latency of VEPs were obtained at the same frequency with four different levels of contrast (5, 25, 50 and 100%) and then logarithmic contrast sensitivities were extrapolated based on these data. The findings of the two tests were compared with Bland - Altman agreement, relevant maps and correlation methods.

The mean differences between VEP based on amplitude and latency findings with Freiburg were 0.32 ± 1.15 and -0.18 ± 0.77 log unit at 1 cpd and -0.25 ± 1.56 and -0.12 ± 0.83 log unit at 5 cpd respectively. The 95% limits of agreement between two methods in the same sequence were ±2.25 and ±1.5 log unit at 1 cpd and ±3.05 and ±1.62 log unit at 5 cpd. Also, the mean differences based on the area under the curve of contrast sensitivity function were -0.13 ± 2.40 and -0.65 ± 1.33 in comparison of VEP amplitude and latency respectively. The 95% limits of agreement in the same sequence were ±4.7 and ±2.6. There were high and significant correlation between “difference between the two methods” and “the average of the two methods” based on the area under the curve of contrast sensitivity function, amplitude at 1 and 5 cpd, and latency only at 5 cpd (0.81 < r < 0.98, P = 0.000).

In the range of the SFs of present study which are the low and medium frequencies of the visual system, in the higher contrast sensitivity, VEP overestimates contrast sensitivity compared to Fr psychophysical test and in the lower contrast sensitivity; Fr test overestimates contrast sensitivity compared to the VEP.