A form of colour-blindness caused by a defect in the functioning of one of the three visual pigments in the cones of the retina, leading to a form of colour vision in which only two of the three primary colours (1) can be perceived and therefore any spectral hue can be matched by only two primary colours, the most common form being deuteranopia. Also called anomalous dichromasy, anomalous dichromatism, anomalous dichromatopsia, anomalous dichromopsia. See also protanopia, tritanopia. Compare anomalous trichromacy. anomalous dichromat n. A person with anomalous dichromacy.