The effect of reduced contrast sensitivity on colour vision testing.

To assess the effect of reduced contrast sensitivity on three commonly used colour vision tests in order to establish key discrepancies that may be relevant for clinical practice. A prospective non-interventional clinical study of colour vision testing using three commonly used devices: Ishihara and Hardy-Rand-Rittler (H-R-R) pseudoisocochromatic plate tests, and Farnsworth D-15 arrangement test performed under progressively reduced contrast sensitivity conditions achieved with a neutral density filter bar. The Pelli-Robson contrast sensitivity (PRCS) at which 5% of the population should first experience a 10% reduction in colour vision testing from baseline was calculated for each of the three colour vision devices: Farnsworth D-15 test: 1.81 log contrast sensitivity (CS), H-R-R test: 1.69 log CS, and Ishihara test: 1.34 log CS. Single factor repeated measures analyses, conducted separately at each contrast sensitivity level, revealed no difference between the colour vision testing devices at PRCS ≥1.80 log CS (P ≥ 0.367). However, in all PRCS ≤1.65 log CS, the differences were statistically significant (all P ≤ 0.004), demonstrating a significantly lower percentage of errors in the Ishihara test compared with both the Farnsworth D-15 (P < 0.023) and H-R-R (P < 0.035) tests. At high contrast sensitivities, all colour vision tests function almost equally; however, at decreased levels of contrast sensitivity, H-R-R and Farnsworth D-15 are more greatly affected.