What Is Achromatopsia

Achromatopsia is a rare hereditary vision disorder affecting the cone photoreceptor cells, resulting in an absence of colour vision along with additional visual problems. There are two main types of cells in the retina responsible for capturing the visual field; the rod cells and the cone cells. We use our rod cells at night time and in low light, but they are not sensitive to colour and do not provide detailed vision. We use our cone cells in bright light. They are responsible for our colour vision and for our central, reading vision. Genetic changes or mutations in genes that function in cone cells are responsible for achromatopsia. Individuals with achromatopsia have reduced visual acuity and are completely or almost fully colour blind; however the condition is not progressive and it does not lead to blindness.

What are the symptoms of achromatopsia?

The condition is often first noticed in a young child by their parents, as children with achromatopsia may dislike bright lights and often avoid the daylight (known as photophobia). Nystagmus is another symptom of the condition, where their eyes may involuntary move and “dance”. Judging from their behaviour some parents may notice that their child’s vision may be reduced or blurred. However, most children with achromatopsia have no problem with mobility or getting around.

What is the cause of achromatopsia and how is it inherited?

To date, mutations in one of five genes are known to cause achromatopsia. The condition is inherited in an autosomal recessive manner, which means that an affected individual inherits a mutated copy of an achromatopsia-linked gene from both parents. Most often, the parents of an individual with achromatopsia each carry one copy of the mutated gene, but do not show signs and symptoms of the condition. 

What treatments are available?

The vision of people with achromatopsia decreases as the levels of light increase. In regular home lighting indoors, or outdoors just after dawn or just before dusk, some people with achromatopsia adapt to their reduced level of visual function without resorting to tinted lenses. Instead, they use visual strategies such as squinting or shielding their eyes or they position themselves in favourable light. Others sometimes wear medium tinted lenses in such settings. However, in full sunlight outdoors, or in very bright indoor spaces, almost all people with achromatopsia use very dark tinted lenses in order to function with a reasonable amount of vision, since they do not possess functioning cone photoreceptors needed in order to see well in these types of settings. Two of the most common genes linked to the condition (CNGB3 and CNGA3) account for 75% of achromatopsia cases, making this condition potentially amenable to gene therapy. Based on a number of successful results in animal models of achromatopsia, a number of groups have initiated human gene therapy clinical trials. These trials plan to deliver a “normal” copy of the mutated gene back to retina, in theory restoring cone function and visual function.

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