Deuteranopia: Green Colour Blindness Explained
Deuteranopia is a form of colour vision deficiency caused by the complete absence of M-cones (medium-wavelength sensitive cone cells). It is classified as red-green colour blindness and is one of the most common forms of CVD. People with deuteranopia are sometimes described as green-blind.
Key Facts
- Prevalence: ~1% of males; under 0.01% of females
- Most common severe form of red-green CVD in males
- Cause: Absence of M-cones; X-linked recessive inheritance
- Key difference from protanopia: Red objects retain normal brightness (no luminosity reduction)
How Deuteranopia Affects Vision
With only L-cones and S-cones functioning, deuteranopes perceive colour along a limited axis. Specifically:
- Red and green appear very similar — both may look brownish, yellowish, or tan
- Red and yellow may be confused with certain shades of green
- Purple appears as blue (since the green component of purple is absent)
- Unlike protanopia, red objects do not appear darker — this is the key clinical distinction
The colours that remain clearly different are those along the blue-yellow axis. Blues and yellows remain relatively distinct, while the red-green portion of the spectrum collapses.
Deuteranopia vs. Deuteranomaly
| Deuteranopia | Deuteranomaly | |
|---|---|---|
| M-cones | Absent | Present, shifted |
| Severity | More severe | Usually mild–moderate |
| Prevalence | ~1% of males | ~5% of males |
| Vision | Dichromacy | Anomalous trichromacy |
Deuteranomaly is the single most common form of colour blindness, affecting ~5% of males. It involves M-cones that are present but shifted in their peak sensitivity toward the L-cone range. The result is reduced but not eliminated ability to distinguish red from green.
Inheritance
Like protanopia, deuteranopia follows an X-linked recessive inheritance pattern. The responsible gene is OPN1MW on the X chromosome.
- Colour-blind father + non-carrier mother → daughters are all carriers; no sons affected
- Carrier mother + unaffected father → 50% of sons colour-blind; 50% of daughters are carriers
Diagnosis
The Ishihara test is effective at screening for deuteranopia. The diagnostic plates in the full 38-plate set include transformation plates that show different numbers depending on whether the deficiency is protan or deutan. For definitive diagnosis, an anomaloscope provides the most accurate classification.
Frequently Asked Questions
Is deuteranopia more common than protanopia? Deuteranomaly (shifted M-cones) is far more common. In terms of complete dichromacy, deuteranopia and protanopia have similar prevalence (~1% each in males).
Can people with deuteranopia drive safely? Yes, in most jurisdictions. Positional cues from traffic lights (top = red, middle = amber, bottom = green) are sufficient. Most countries do not restrict driving licences for standard red-green colour blindness.
Do colour-correcting glasses work for deuteranopia? Some people benefit, though results vary considerably. Filters work by increasing the separation between red and green wavelengths reaching the remaining cones.
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