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 function of the specialist light-sensing cells called cones, which are responsible for our reading vision and colour vision and allow us to see fine detail and in bright light.

What causes achromatopsia

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.

A person with achromatopsia will have limited or no colour vision and may have extreme light sensitivity (photophobia) and reduced central vision. They often prefer dim lighting. They also often have 'nystagmus' - rapid involuntary eye movements.

The severe visual impairment can often affect the ability to carry out everyday activities.

Unfortunately, there’s currently no cure for achromatopsia – and the focus is on managing the symptoms. But clinical trials of cutting-edge gene therapies that offer the potential to reverse the visual problems associated with achromatopsia.

Estimates suggest that achromatopsia affects around 1 in 30,000 people worldwide.

Achromatopsia is different to more common forms of colour blindness, where people can perceive colour but 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 people have no colour vision and, more severely, reduced central vision.
• Incomplete achromatopsia. This is a milder form of the condition associated with residual cone cell function, where limited colour vision is present, and other vision problems, such as photophobia, tend to be less severe.

What causes achromatopsia?

Achromatopsia is an inherited condition where a child is born without functioning cone cells. 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.

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

But there are other disease-causing genes yet to be identified.

Achromatopsia is inherited in an autosomal recessive pattern. In this type of inheritance, both parents are 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.

When faults occur in the genes that cause achromatopsia, the cone cells don’t respond to light correctly. In people with complete achromatopsia, their cone cells do not work at all – causing total colour blindness, severely reduced central vision and light sensitivity.

But people with incomplete achromatopsia will retain some cone function, which means they will have some limited colour vision and their other vision problems tend to be less severe.

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 distinct from inherited forms of achromatopsia.

What are the symptoms of achromatopsia?

As well as colour blindness, a person with achromatopsia may experience some or all the following symptoms:

• Extreme light sensitivity: This can make it very uncomfortable, or even painful, to be in bright light (photophobia). This is sometimes known as day blindness.
• Reduced vision: Central vision is reduced. People may have a blind spot in the centre of their vision – which makes it difficult to see fine details – and a reduced central visual field.

Involuntary rapid eye movements are often present from birth but can become less noticeable over time.

•  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.

How is achromatopsia treated?

Unfortunately, there is currently no cure for achromatopsia. But a variety of aids and adjustments can help people to manage some of the challenges of living with the condition. These include:

• Wearing prescription glasses or contact lenses. Correcting refractive errors may help improve a person’s vision.
• Tinted lenses (spectacles or contact lenses) can help to reduce sensitivity to bright light.
• Special sunglasses. Some people may find wearing dark-tinted or UV-blocking sunglasses helpful, even indoors.

Living with 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. The focus is helping people manage their symptoms, adapt to their surroundings and carry out everyday activities.

A low vision assessment is essential and 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. Using these can help with looking at electronic device displays that may be too bright.
• Vision aid technologies. For example, a handheld scanner or phone app can be used to identify the object’s colour. Such assistive technologies are rapidly helping to improve people’s functional vision.

What’s the latest research 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.

Last updated August 2023
Approved by Prof Michel Michaelides, Moorfields Eye Hospital
and Prof Omar Mahroo, Moorfields Eye Hospital