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To evaluate the effects of the ChromaGen contact lens (CCL) on best-corrected visual acuity, contrast sensitivity and pseudoisochromatic test plate performance in patients with congenital colour vision deficiency (CVD).CCLs were inserted into 50 eyes of 25 patients with congenital red-green CVD. The patients were tested with the Ishihara and Hardy-Rand-Rittler test plates before and after the insertion of Magenta 2, Magenta 3, and Violet 3 CCLs. The patients' mean numbers of recognised symbols were calculated and the most appropriate CCL was determined for each eye. The best-corrected visual acuity for both far and near vision and contrast sensitivity were evaluated before and after the insertion of the appropriate CCLs, and the results were compared.The mean age of the patients was 26.56 ± 10.30 years. While all CCLs increased the mean numbers of recognised symbols on the Ishihara (p < 0.001 for all), Magenta 3 was observed to be the most useful CCL. On the other hand, while all CCLs increased the mean numbers of recognised symbols on Hardy-Rand-Rittler (p < 0.001 for all), Magenta 2 and Magenta 3 were detected as the most useful CCLs. After insertion of the most appropriate CCL for each eye, the mean best-corrected visual acuity for both far and near vision were decreased (p < 0.001 for both). Statistically significant alterations were also detected at some spatial frequencies of contrast sensitivity measurements.CCLs decrease the far and near best-corrected visual acuity, and static and dynamic contrast sensitivity at some spatial frequencies, and invalidate the pass criteria of pseudoisochromatic test plates by increasing the number of recognised symbols.