Also known as “total colour blindness,” achromatopsia (ACHM) is a genetic syndrome characterized by the inability to perceive colour. Though experiences of colour sensations vary, many with the condition can only see black, white, and shades of grey—this is often called “complete achromatopsia,” and differs from the more common forms of colour blindness involving difficulty distinguishing between certain colours. Others can see some additional colours and shades under certain conditions but still within a limited spectrum (sometimes called “dyschromatopsia”), and still, others have difficulty seeing clearly in high-light environments—outside during a sunny day, for instance—or are extremely sensitive to such light (photophobia). The syndrome affects approximately 1 in 30,000 people, and its symptoms are usually noticed during the first few months of life.
The genetics of achromatopsia are varied, involving one of five genes: CNGA3 and CNGB3 are associated with the vast majority of cases, and the genes GNAT2, PDE6C, and PDE6H underlie the rest. Gradual deterioration of the retina’s cone and rod photoreceptors is the mechanism underlying vision loss in retinitis pigmentosa (RP) and similar retinal diseases. With achromatopsia, it is primarily the cone photoreceptors that are affected, disrupting their ability to transmit visual information to the brain. Since it is the cones that are responsible for colour vision, their reduction or complete loss has a predictable effect: a loss of the ability to perceive colour. Cone photoreceptors are responsible for central, high-acuity vision as well, which is why many with the disorder live with a severe impairment of central vision. In patients with complete achromatopsia, all cone photoreceptors have died as a result of the mutation.
The term “achromatopsia” became widely used after the publication of Oliver Sacks’ 1997 book The Island of the Colorblind, where he recounts his time living among a community of achromatopes inhabiting the island of Pingelap in the South Pacific. Sacks describes in detail the accounts of achromatopic vision provided by the Pingelapese.
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Updated on August 23, 2018.
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