Abstract
AIM: To compare the Ishihara test errors scores of colour vision deficiency (CVD) subjects when wearing four different types of red-tinted contact lenses (RCL) that differ in their transmittance as determined using a spectrophotometer. METHODS: Six congenital CVD subjects volunteered to participate in this study. Ishihara plates were used to determine the colour vision errors made, whereas Farnsworth-Munsell 100 Hue test was conducted to determine the total error scores (TES) and type of CVD. Four types of RCL (Types A, B, C and D) were inserted in the non-dominant eye and tested in a randomised manner by a masked operator. Errors scores in Ishihara test were determined at baseline without any contact lens and after wearing the four different RCL. The subjects were then divided into two groups based on the mean TES. RESULTS: Repeated measures ANOVA with Greenhouse-Geisser corrections showed that there was a highly significant effect of RCL type on Ishihara error score [F(2.056, 10.282)=30.214, P<0.001]. Error scores with RCL Type B were significantly lower than errors made when no lens was worn, and with RCL Type C and Type D (all P<0.001). Error scores with RCL Type B were also lower than those made with RCL Type A, however, they were not significantly different. For subjects with TES values less than 180, RCL type B showed the largest improvement in Ishihara error score (50%) compared to the other three RCLs. RCL type A showed the best performance in TES value of more than 180, with an improvement of 80% in Ishihara score. RCL Type A has the lowest transmittance at the confusion wavelength (450-568 nm), followed by RCL Types B, D and C. CONCLUSION: This study shows that RCL can improve Ishihara error scores. RCL with lower transmission at 450-568 nm and 90% transmittance beyond 637 nm are the most effective. Lenses which could block more light between 550-580 nm are more effective for colour defectives with more severe colour defects.