Achromatopsia · Rod monochromacy
Achromatopsia (rod monochromacy)
With almost no working cones, the world is seen only through differences in brightness. Reduced visual acuity, severe glare sensitivity, and nystagmus come with it.
- Working cells
- Rods only
- Inheritance
- Autosomal recessive
- Prevalence
- ~1 in 30,000
- Associated symptoms
- Low vision, glare, nystagmus
How it works
In achromatopsia, none of the three cone types works properly, and vision relies mainly on the rods — the cells used in dim light. Variants in CNGA3 and CNGB3 are the most common causes; GNAT2, PDE6C, PDE6H, and ATF6 are among the others.
Rods saturate in bright light, so daylight is intensely dazzling, and because the cone-rich fovea can't be used properly, visual acuity is greatly reduced (usually around 0.1 on the decimal scale, roughly 20/200).
It is inherited in an autosomal recessive pattern: a person must inherit one variant from each parent.
What you see
Colors can barely be distinguished; objects are seen only by brightness (light and dark). A red and a green of the same brightness look like the same gray.
The table below is an approximation that removes color and keeps only luminance. In reality, rods have a different spectral sensitivity, so greens and blues feel relatively bright and reds feel dark.
| Color | Normal vision | Achromatopsia (rod monochromacy) |
|---|---|---|
| Red | #D7263D | #707070 |
| Orange | #F28C28 | #A5A5A5 |
| Yellow | #F2CD37 | #D0D0D0 |
| Green | #2E9E44 | #8A8A8A |
| Teal | #1A9E9A | #8E8E8E |
| Blue | #2F6BD8 | #707070 |
| Purple | #7E3FB2 | #5E5E5E |
| Pink | #E86FA6 | #989898 |
| Brown | #8B5A2B | #656565 |
| Gray | #8C8C8C | #8C8C8C |
Simulation: an approximation that removes color and keeps only luminance (Rec.709). Actual vision may vary with lighting and the individual.
How common is it?
It is estimated to affect about 1 in 30,000 people worldwide (MedlinePlus Genetics).
In some places, such as Pingelap Atoll in the Pacific, several percent of residents have achromatopsia — explained by a past event that drastically shrank the population (the founder effect).
Easily confused colors
- All colors of equal brightness (red ↔ green ↔ gray, etc.)
- Dark red ↔ black
Everyday tips
- Dark sunglasses or red-tinted filter lenses are commonly used to reduce glare. Consult a low vision clinic when choosing lenses.
- Low vision aids such as magnifiers, screen zoom, and high-contrast modes help.
- Gene therapy clinical trials have been carried out, but there is no standard treatment yet.