Sensitivity of screening tests for S-cone discrimination

Abstract

We evaluated tritan screening tests in color normals by producing S-cone discrimination loss with reduced illumination. The Tokyo Medical College plates, the Rabkin plates, the Velhagen plates, and the Minimalist test were compared to the Standard Pseudoisochromatic Plates, Part 2 (SPP-2) for which we have previously reported data. We used six light levels ranging from 0.1 to 63 lux. Seventeen observers with normal color vision served in the experiment; seven older observers (median age 49) and ten younger observers (median age 28). All performed all tests correctly at 63 lux. There were statistically significant differences between the younger and older groups on all tests. For pseudoisochromatic plates, the Rabkin plates were the least sensitive to reduced illumination while the Tokyo Medical College plates showed high sensitivity. The four plates of the Velhagen test, showed differing sensitivity. The error scores on the Minimalist test increased with decreasing illumination level. The error scores of the tritan series were always greater than those of the protan and the deutan series. The Velhagen and the Minimalist test allow estimation of graded sensitivity loss comparable to the SPP-2.