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What Is Achromatopsia?

Achromatopsia (also called rod monochromacy or total color blindness) is a condition in which all cone cells in the retina are absent or completely non-functional. Since cones are responsible for all color vision and fine-detail sharp vision (especially in daylight), people with achromatopsia see the world entirely in shades of grey similar to an old black-and-white photograph.

Achromatopsia is extremely rare, affecting approximately 1 in 30,000 people worldwide. Unlike other forms of color blindness, it affects men and women equally it is not X-linked.

Types of Achromatopsia

There are two main categories:

• Rod monochromacy (complete achromatopsia) All cones are absent or non-functional. Vision relies entirely on rod cells. Very low visual acuity (typically 20/200 or worse), severe light sensitivity (photophobia), and nystagmus (involuntary eye movements) are common.
• Cone monochromacy (incomplete achromatopsia) Only one type of cone (e.g., S-cones) is functional. Color discrimination is absent because no two cone types are available for comparison. Visual acuity and light sensitivity may be closer to normal.

Symptoms of Achromatopsia

• No color perception everything appears in black, white, and grey
• Severe light sensitivity (hemeralopia) bright light is painful
• Reduced visual acuity fine details are blurred
• Nystagmus rhythmic, involuntary eye movements
• Normal or near-normal vision in low light

Causes of Achromatopsia

Complete achromatopsia is a genetic condition, most commonly caused by mutations in the CNGB3 or CNGA3 genes encoding cyclic nucleotide-gated channels in cone photoreceptors. It follows an autosomal recessive inheritance pattern both copies of the gene must be affected for the condition to manifest.

How Is Achromatopsia Detected?

Standard Ishihara plates designed primarily for red-green color blindness can reveal achromatopsia when a person fails all colored number plates, as no color distinctions are possible. A comprehensive color vision assessment may also use the Hardy-Rand-Rittler (HRR) test or electroretinography (ERG) for clinical confirmation.

Our 18-plate online test includes achromatopsia detection. If you cannot read any of the Ishihara numbers, achromatopsia or severe CVD of another type may be present.

Designing for Achromatopsia

Designing for achromatopsia is the most demanding accessibility scenario: if your design works for achromatopsia, it works for all other CVD types too. Key guidelines:

• Ensure all information is conveyed through structure, text labels, or icons never color alone
• Use high-contrast black-and-white patterns to differentiate chart elements
• Avoid low-contrast greyscale combinations light grey on white is invisible
• Test your design under Achromatopsia mode in the simulator to see the full greyscale version
• Meet WCAG AAA (7:1) contrast requirements wherever possible