Limitation of standard pseudoisochromatic plates in identifying colour vision deficiencies when compared with genetic testing

Abstract

Purpose: The Ishihara pseudoisochromatic (PIC) plate test is the most used test for identifying red-green colour-deficient individuals, but it is not known how the Ishihara results compare with that of genetics testing. Here, the outcome of genotype analysis of OPN1LW and OPN1MW was compared with that of the Ishihara (24-plate ed., 1964) and the Hardy-Rand-Rittler (4th ed. 2002) PIC plate tests.

Methods: Healthy participants with normal habitual visual acuity (n = 454, 16-24 years; 193 males; logMAR ≤ 0.00) gave saliva samples for opsin gene analysis and performed the two PIC plate tests as part of a cross-sectional study. The criteria for failing the PIC tests were according to manufacturers' instructions. DNA was extracted and used in genotyping assays of OPN1LW and OPN1MW genes from each participant using the Agena MassArray genotyping system.

Results: Ten male (5.2%) and 3 (1.1%) female participants were identified as red-green colour deficient based on PIC tests alone. The combination of MassArray and PIC test results identified 10.4% of male and 0.8% of female participants to be colour deficient (males: 0.5% protan and 9.9% deutan; females: 0.8% deutan). Hardy-Weinberg calculations based on male frequencies from combining the MassArray and the PIC test results gave female frequency estimates of colour deficiency and carriers closely matching measured frequencies.

Conclusions: MassArray identified twice as many colour-deficient males as identified from PIC tests alone. Combining results from MassArray and the PIC tests proves to be more reliable than any single test at correctly identifying red-green colour-deficient individuals and carriers.

Keywords: Hardy-Rand-Rittler test; Ishihara test; colour vision deficiency; colour vision testing; genetic testing; opsin genes.