Protanomaly · protan anomalous trichromacy
Protanomaly (red-weak)
The L cones are present, but their sensitivity is shifted toward M, weakening red-green discrimination and making red look dull and dark.
- Altered cones
- L shifted toward M (L′)
- Inheritance
- X-linked recessive
- Prevalence
- Men ~1.1% · women ~0.03%
- Severity
- From mild to near protanopia
How it works
People with protanomaly have all three cone types, but the L-cone photopigment is shifted toward the wavelengths of the M cones — a form of anomalous trichromacy. It usually stems from a hybrid gene formed when the L and M photopigment genes on the X chromosome mix.
The closer the L and M sensitivity curves are, the smaller the difference between the signals from the two cone types, and the weaker red-green discrimination becomes. Depending on how close the curves are, people range from barely inconvenienced to nearly protanopic.
As in protanopia, brightness sensitivity to long wavelengths tends to drop, so red looks slightly darker and muddier.
What you see
Vivid reds and greens are usually distinguishable, but muted colors (olive, khaki, ochre, yellow-green), small areas, and dim light easily cause confusion.
The table below uses a 60% severity simulation. Actual severity varies from person to person — try changing the severity in the simulator.
| Color | Normal vision | Protanomaly (red-weak) |
|---|---|---|
| Red | #D7263D | #8E543A |
| Orange | #F28C28 | #C29718 |
| Yellow | #F2CD37 | #E8CB26 |
| Green | #2E9E44 | #8D9340 |
| Teal | #1A9E9A | #80979A |
| Blue | #2F6BD8 | #2473DA |
| Purple | #7E3FB2 | #3F56B4 |
| Pink | #E86FA6 | #A586A6 |
| Brown | #8B5A2B | #745E27 |
| Gray | #8C8C8C | #8C8C8C |
Simulation: Machado, Oliveira & Fernandes (2009) matrices at 60% severity. Results may differ from reality depending on your monitor and individual differences.
How common is it?
It is reported in about 1.1% of men and about 0.03% of women of European ancestry (Sharpe et al., 1999).
Dot-plate tests can't reliably separate protanomaly from deuteranomaly. The standard for classifying the type is a test such as the anomaloscope. Test methods compared
Easily confused colors
- Yellow-green ↔ yellow ↔ orange, olive ↔ brown
- Purple ↔ blue, pink ↔ light gray
- Red text ↔ black text (at small sizes)
Everyday tips
- For information defined by position, like traffic lights, make a habit of checking the position first.
- For material coded only by color, like charts or subway maps, zooming in or keeping the legend right beside it cuts down on mistakes.
- Many people with mild color weakness go through daily life without ever knowing it. If it rarely causes problems, there's no need to worry.