Objective Measurement of the Chromatic Contrast Sensitivity Using VEP: Studies on Normals and Color Vision Defectives

Abstract

Abstract: : Purpose: To develop a practical and rapid method of determining the chromatic contrast sensitivity function (CCSF) which will be useful for testing both normals and color defective individuals. Methods: The swept parameter VEP technique (Norcia AM and Tyler CW, 1985) was modified to determine the chromatic contrast sensitivity function (CCSF). Both eyes were stimulated simultaneously by vertical sinusoidal iso-luminant chromatic gratings presented on a color monitor. The visual angle of the stimulus was 10 x 8 deg, and the two colors of the gratings were selected from the colors on the dichromatic iso-chromatic lines. Steady-state VEPs were recorded during a continuous decrease of chromatic contrast at 10% per second from 100% to 0%. The amplitudes of the VEP component at twice of the temporal frequency of the stimulus were evaluated, and their changes as the contrast decreased were determined as the CCSF. VEPs elicited by 6, 8, and 10 Hz temporal frequencies, and 0.5, 1, and 2 c/deg spatial frequencies were recorded from two deuteranopes and seven normal volunteers. Results: The CCSF to one color stimulation was successfully determined within 15 seconds in all subjects and was reproducible within a subject. The CCSF for tritanopic iso-chromatic colors decreased with a decrease of chromatic contrast in both normals and deuteranopes. Relatively small and flat CCSF were observed at 40% and higher contrast range in two deuteranopes compared with those of normals. Large amplitudes and clear curves were extracted from the VEPs at 2 c/deg and 6 Hz. The VEP amplitudes decreased and the differences between subjects were increased with an increase of both spatial and temporal frequencies. This method was also confirmed to be an objective measure of spatial/temporal frequency characteristics (MTF) of the human color vision system. Conclusion: Large amplitude and reproducible CCSF curves can be obtained by a modified sweep parameter technique within 15 sec. Relatively small amplitudes of CCSF were obtained in deuteranopes indicating that this technique is probably an objective measure of the color vision.

Keywords: color vision • electrophysiology: non-clinical