What does deuteranopia mean?
Deuteranopia is a specific type of colour vision deficiency in which the retina's medium-wavelength cone cells — those responsible for perceiving green light — are missing or do not function properly. The result is a reduced ability to distinguish between shades of green, red, yellow, and brown, since the affected person must judge colours using only two working cone types instead of the usual three. Deuteranopia is inherited, linked primarily to the X chromosome, and therefore affects men far more frequently than women; it is the most common form of complete red-green colour blindness. The word appears mainly in medical, scientific, and design contexts — for example, when discussing genetic testing, diagnosing vision problems, or ensuring that websites and signage remain legible to colour-blind users. Related terms include deuteranope, meaning a person who has the condition, and deuteranopic, its adjectival form. Understanding deuteranopia matters both clinically and practically, since even small design choices can determine whether someone can read a chart or distinguish a warning signal.
nounA form of red-green colour blindness caused by the absence or malfunction of the medium-wavelength (green-sensitive) cone cells in the retina, resulting in reduced sensitivity to green light and difficulty distinguishing greens from reds.
- A hereditary deficiency of medium-wavelength (M-) cone photoreceptors in the retina, producing red-green colour confusion; the most common form of dichromatic colour vision deficiency in humans.
"Because of his deuteranopia, he could not tell the ripe tomatoes from the unripe ones by colour alone."
"The ophthalmologist's tests confirmed that his colour confusion stemmed from deuteranopia rather than any disease of the eye."
"Designers increasingly check interfaces against deuteranopia to ensure that red and green indicators remain distinguishable to all users."
Rarely used; deuteranopia normally functions as an uncountable noun referring to the condition generally. A plural may appear when discussing multiple individual cases or degrees of severity.
"The study compared mild and severe deuteranopias across several family lineages."
Roughly one in twelve men has deuteranopia, yet many never discover it until a routine eye test — because their brains quietly learned to compensate.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of deuteranopia
Deuteranopia derives from Greek roots: 'deuteros', meaning 'second', combined with '-anopia', from 'an-' (without) and 'ōps' (eye), so literally 'second-sight-blindness' — referring to the second of the three cone systems. The term was coined in the late nineteenth century as part of the systematic classification of colour vision defects developed by researchers such as John William Strutt (Lord Rayleigh). It shares its 'deuteros' root with words such as deuterium, Deuteronomy, and deuteragonist, while its '-opia' element connects it to other visual terms like myopia and hyperopia.
Word family
Usage notes
A technical term used chiefly in optometry, ophthalmology, genetics, and accessibility contexts. It is countable when referring to individual cases ('a mild deuteranopia') but is more often used as an uncountable mass noun. In everyday speech, people usually say 'colour blindness' or 'red-green colour blindness' rather than 'deuteranopia'. British English typically spells the related adjective form with '-colour-' compounds (e.g. 'red-green colour blindness'), while American English uses 'color'.
Don't confuse with
Protanopia results from a defect in the long-wavelength (red-sensitive) cones, whereas deuteranopia results from a defect in the medium-wavelength (green-sensitive) cones.
Tritanopia is an extremely rare blue-yellow colour blindness affecting short-wavelength (blue) cones, whereas deuteranopia is a far more common red-green defect.