Masking Colour Blindness: A Case Report.

Colour vision is an important aspect of visual function that might help individuals in doing daily activities. Some occupations require and test for good colour discrimination. We describe a case of a 20-year-old man who was referred to our centre to establish if he had colour vision deficiency (CVD). He had been tested for this twice as part of his assessment to enter the police force. At the first examination, he had normal colour vision, while the second examination revealed CVD, thus the patient was referred for confirmation. Colour vision tests using the Ishihara plates showed normal results with each eye, while a Roth test revealed an unspecified CVD in the right eye and deuteranopia in the left eye. During the evaluation, we noticed he was using a red-tinted contact lens in the right eye, and was wearing a red mask with transparent red plastic in the upper part. After removal of the contact lens and mask, he was asked to repeat the examinations and it revealed deuteranopia in both eyes. A tinted contact lens is a corrective device that can help to enhance colour discrimination in CVD subjects. However, in this case the tinted contact lens was used inappropriately to manipulate the colour vision examination. We highlight the case to raise awareness that the use of red contact lenses and red filters can mask CVD.