Purpose: To assess the Medmont C100 test as a colour vision screening tool. Methods: One hundred and seventeen young male adults were screened with the Medmont C100, Ishihara plates, and the screening mode of the Oculus Anomaloscope tests. All subjects were tested under constant room illumination, namely that of a day light fluorescent lamp at 200 lux. Inclusion criteria were visual acuities (VA) of 20/20 or better with or without correction and absence of known ocular pathologies. Aided and unaided visual acuities were measured with the Snellen VA chart. Results: Five out of the 117 subjects, were found to have red-green colour vision deficiency (CVD) with Ishihara and anomaloscope tests indicating a 4.7% CVD prevalence, while the Medmont C100 test yielded 33 cases ofred-green deficiency indicating CVD prevalence of 28%. With the Ishihara test, all five subjects were identified as deutans, while the anomaloscope revealed three as deutans and two as pro-tans, and the Medmont C100 test identified all 33 cases as protans. Conclusion: The Medmont C100 test yielded significantly higher prevalence of protan CVD compared with the Ishihara platesand Anomaloscope tests. These findings suggest that caution should be taken when using Medmont C100 test for colour vision screening as it tends to give more false positive results with bias for pro-tans. (S Afr Optom 2011 70(1) 14-20)

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