What does dichromat mean?
A dichromat is a person whose eyes contain only two working types of cone cell instead of the three that produce ordinary colour vision. Because human colour perception normally depends on comparing signals from long-, medium-, and short-wavelength cones, a dichromat — missing one of these channels — cannot distinguish certain colours that others see as clearly different, most commonly shades of red and green, and occasionally blue and yellow. The condition is usually inherited on the X chromosome, which is why it affects far more men than women. The noun belongs chiefly to the vocabulary of optometry, psychology, and vision science, alongside related terms such as 'trichromat' for someone with normal colour vision and 'monochromat' for someone who perceives almost none at all. In everyday conversation, speakers are far likelier to say simply 'colour-blind', but 'dichromat' offers a scientifically exact way to name this specific kind of visual difference.
nounA person who has dichromatic vision — that is, whose retina contains only two functioning types of cone cell rather than the normal three, causing colour-blindness.
- A person with dichromatic vision, having two functional types of retinal cone cell and consequently a form of colour-vision deficiency.
"As a dichromat, he could not distinguish red from green at the traffic light without memorising their positions."
"Tests revealed that the artist was a dichromat who had learned to compensate by relying on tone and texture rather than hue."
"For a dichromat, the Ishihara plate shows no number where most readers can clearly make one out."
Standard regular English plural.
"Dichromats often develop strategies for navigating a world designed around trichromatic vision."
Roughly one man in twelve is a dichromat — yet most reach adulthood without ever realising the world looks different to them than to everyone else.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of dichromat
The word 'dichromat' combines the Greek prefix 'di-' meaning 'two' with 'chroma' meaning 'colour'. It arose within nineteenth-century scientific writing on colour vision, when researchers first classified colour deficiencies by the number of spectral sensations an observer could perceive. Its relatives from the same Greek root include 'chromatic', 'chromosome', and 'polychrome'; its direct counterparts are 'trichromat' and 'monochromat', formed with the prefixes for 'three' and 'one'.
Related word forms
How dichromat is actually used
A technical term used mainly in optometry, ophthalmology, psychology, and scientific writing about vision; it is precise but uncommon in everyday speech, where 'colour-blind' or 'colour-deficient' is more typical.
Easily confused with dichromat
A trichromat has normal three-cone colour vision, whereas a dichromat has only two functioning cone types and is therefore colour-deficient.
A monochromat has only one functional cone type and perceives essentially no colour at all, while a dichromat retains limited two-colour perception.