Objective evaluation of binocular function with pattern reversal VER. I. Effect of contrast.

The effect of change of contrast on the pattern reversal monocular VER, binocular VER, and binocular summation (binocular VER amplitude/monocular VER amplitude) was studied in normal subjects. The monocular VER amplitudes showed significant increase until the 0.50 contrast and saturation above that contrast. The largest binocular VER amplitude was observed at 0.20 contrast, and the amplitude tended to decrease with increasing contrast. The value of the binocular summation was highest at 0.20 contrast and decreased significantly with increasing contrast. At high contrast, there was no significant binocular summation. The difference of peak time (phase) between the binocular and the monocular VER was greatest at low contrast and decreased with increasing contrast. These results are explained by the difference of saturation level between the binocular and monocular systems. Our findings lead us to advocate strongly the use of low- to midlevel contrast for evaluating binocular function with pattern reversal VER in clinical ophthalmology.