Chromatic discrimination in young carriers of red-green colour vision deficiencies
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Purpose: Visual discrimination skills, like discrimination of motion and colour, improve throughout adolescence in normal trichromats. Some adult carriers of red-green colour vision deficiencies exhibit reduced colour discrimination, but little is known about colour discrimination abilities in young carriers. The aim of this study was to assess the colour discrimination abilities of young obligatory carriers. Methods: 100 normal trichromatic females (aged 18.28 (±7.11) years) and 30 obligatory carriers of red-green colour vision deficiencies (8 protan carriers and 22 deutan carriers, aged 32.07 (±15.5) years) were tested with a battery of colour vision tests comprising Ishihara (24 pl. ed.), Hardy-Rand-Rittler 4thed. (HRR 2002), Neitz Test of Color Vision (NTCV), Cambridge Colour Test (CCT), Farnsworth-100-Hue Test (FM100-Hue), HMC anomaloscope (both Rayleigh and Moreland matches) and Medmont C-100. The results are presented for four different age groups (9-12, 18-29, 30-39 and 40+). Results: Carriers aged 9-12 years failed the pseudoisochromatic (PIC) tests more often than their normal trichromatic peers. These tests were failed by 80% of deutan carriers and 50% of protan carriers, but only 20% of normal trichromats in the same age group. These figures decreased to 75%, 20% and 12%, respectively, in the 30-39 year age group. Colour discrimination, as assessed by the FM100-Hue test, improved with age for both groups, but the carriers’ performance was, on average, poorer than that of normal trichromats. Variability in the FM100-Hue error scores was significantly greater for the 9-12 year age group, compared to the three older age groups, both for normal trichromats and for carriers. Protan carriers required, on average, more red and deutan carriers required more green, compared to normal trichromatic females, when tested on the Rayleigh match and the Medmont C-100 tests. However, the Medmont C-100 failed to identify protan and deutan carriers amongst the normal trichromats and the null-point settings of all three groups overlapped considerably. Conclusion: The results imply that some young female carriers may have exacerbated problems with colour discrimination due to the combined effects of being a carrier and having an immature visual system. The improvement in colour discrimination with age seen in normal trichromats is also evident in carriers of red-green colour vision deficiencies. Deutan carriers scored significantly worse on the colour vision tests used, which shows that they have poorer colour vision than protan carriers. The results from the Rayleigh anomaloscope and the Medmont C-100 tests imply that it may be possible to classify known obligate carriers as either protan or deutan carriers.