dikromat

Dikromat is a person with dichromatic color vision, in which only two of the three cone photoreceptor types in the retina are functional. Most commonly this means protanopia (absence of L-cones) or deuteranopia (absence of M-cones), together referred to as red–green dichromacy. A rarer form is tritanopia (absence of S-cones), a blue–yellow dichromacy. Because only two cone types operate, dichromats perceive a more limited color palette than trichromats and rely more on brightness and context to distinguish objects.

Causes and inheritance: Protanopia and deuteranopia are usually inherited in an X-linked recessive pattern, so males are disproportionately affected; females are typically carriers. Tritanopia is much rarer and can be inherited in an autosomal way or occur sporadically.

Phenotype and color perception: Dichromats may confuse certain hues, especially reds and greens, or blues and yellows, though they can often identify color by cues other than hue. In daily life, many people adapt and perform tasks with little difficulty, but color-critical activities (e.g., color-based labeling or signaling) may require accommodations.

Diagnosis: Diagnosis relies on color vision testing. Ishihara plates are used to screen red–green defects; anomaloscopy provides precise classification of the dichromatic type; other tests include Cambridge Colour Test.

Prevalence: Red–green dichromacy is more common in men; overall prevalence varies by population but is on the order of a few percent for men of European ancestry and is less common in women; tritanopia is rare.

Management: There is no cure. People may use color-correcting spectacles or contact lenses designed to enhance color discrimination, though benefits vary; technology and apps can aid color identification; workplaces can use noncolor cues to convey information.