Achromatopsia

What is achromatopsia?

Achromatopsia is a rare inherited condition that causes problems in the retina, the light-sensitive tissue at the back of the eye. It affects the specialist light-sensing cells called cones, which are responsible for reading vision and colour vision and allow us to see fine detail and in bright light.

It's different to more common forms of colour blindness, where people have difficulty distinguishing between certain colours, such as red and green, but have otherwise normal vision.

What are the different types of achromatopsia?

There are two forms of achromatopsia, with differing symptoms:

• Complete achromatopsia: No cone cell function at all, so you have reduced central vision and no colour vision.
• Incomplete achromatopsia: A milder form of the condition where there is still some cone cell function, so you have limited colour vision. Other vision problems, such as light sensitivity, tend to be less severe than with complete achromatopsia.

What causes achromatopsia?

Achromatopsia is almost always an inherited condition. It is caused by changes in one of several genes that contain the instructions to make proteins that play an important role in healthy cone cell function.

Light entering the eye stimulates the cone cells, which convert this into electrical signals sent to the brain, where they are interpreted. But in a child born with achromatopsia, the cone cells do not work properly, interfering with the transmission of visual signals from the eye to the brain – causing visual problems.

The most common genes involved are CNGB3 and CNGA3, which together account for around three out of four cases. Genetic changes in other genes called GNAT2, PDE6C, PDE6H and ATF6 can also cause achromatopsia.

There are other disease-causing genes still to be identified.

Achromatopsia is inherited in an autosomal recessive pattern. In this type of inheritance, both parents are usually unaffected carriers – meaning they each carry one copy of the faulty gene and one healthy copy but do not have any symptoms. Each of their children has a one in four chance of having achromatopsia by inheriting a copy of the faulty gene from both parents.

In very rare cases, achromatopsia can be caused by damage to the brain – for example, due to a stroke. This is known as ‘acquired achromatopsia’ (cerebral achromatopsia) and is different from inherited  achromatopsia.

What are the signs and symptoms of achromatopsia?

If you or your child have achromatopsia, you or they may have some or all of these symptoms: 

• partial or complete colour blindness
• extreme light sensitivity (known as photophobia, or day blindness) - this means that bright light can be uncomfortable or even painful
• reduced central vision, for example a blind spot in the centre of your vision
• rapid involuntary eye movements (nystagmus)
• refractive errors: This could be farsightedness (blurry vision when looking at close-up objects) or myopia, also known as near-sightedness, where it is difficult to see distant objects.

Achromatopsia is often noticed in the first few months of life because the child is very sensitive to light. But other symptoms, such as poor vision and colour blindness, may not be noticeable until they are a bit older. Involuntary rapid eye movements are often present from birth but can become less noticeable over time.

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Is achromatopsia serious?

Achromatopsia can cause severe visual impairment, especially if it's complete achromatopsia. It can often affect the ability to carry out everyday activities. 

How is achromatopsia diagnosed?

Achromatopsia is usually diagnosed based on the symptoms you or your child have been experiencing, as well as an eye examination, and the results of eye tests including tests for colour vision. You may also have scans of the eye. Genetic testing can help to confirm the diagnosis. 

What are the treatments for hemianopia?

First, the cause of hemianopia, such as stroke, tumour or head injury, is treated. This may help restore some function of the visual pathway in the brain. Sometimes your vision will improve over time without any treatment, but in many cases it doesn't. 

An eye clinician may recommend different strategies to help with your vision, such as:

• Visual scanning exercises - involve looking to the left and right side systematically to help improve your awareness of the visual field loss and remind you to look into your blind side. For example, you could practice keeping your head still and moving your gaze around to your affected side of vision. Or using puzzles and word search games to improve your visual detection skills.
• Prismatic correction glasses - can help widen your field of view in some circumstances. The prism is worn on the side of the visual field loss, creating a blurred, overlapping image that you can see on your 'good' side. This acts as a prompt to look towards the blind side.
• Visual restorative treatment for hemianopia - Different strategies are available that aim to help you to interpret visual information by building awareness of moving images in your blind field of vision.

There are also practical things you can do to help you to cope with vision problems (see What can help hemaniopia, below).

What can help achromatopsia?

Living with achromatopsia can be challenging, but with the right support, it’s possible to lead an independent life and achieve professional and personal ambitions. 

It's important to get a low vision assessment (at a specialist clinic). This should focus on helping you or your child manage symptoms, adapt to surroundings and carry out everyday activities. It may recommend the use of resources such as:

• Simple visual aids - for example, a magnifying device may make it easier to see details when reading
• Screen readers - so you don't need to look at electronic device displays that may be too bright
• Vision aid technologies - for example, there are handheld scanners and phone apps which can tell you what colour an object is. Technology like this can make a real difference.

What research is there into achromatopsia?

Achromatopsia research is focused on developing cutting-edge gene therapies that aim to deliver a correct copy of the faulty gene into the patient’s cone cells, restoring their function. This approach has only become possible since researchers have identified some of the faulty genes behind the condition.

But there are still more genes that cause achromatopsia to be found. Identifying these genes would mean more people could receive an accurate diagnosis, enabling access to better genetic counselling about how the condition might affect themselves and their families.

See our research projects