Description

Achromatopsia is a rare (1:30,000) inherited retinal degeneration. It is recognised as either a partial or complete absence of colour vision, along with additional visual problems.

This condition is caused by cone photoreceptor cells which do not function properly. Cone photoreceptor cells are one of the two main types of cells in the retina responsible for capturing the visual field. We typically use these cells in bright light conditions and they are important for colour vision, central vision and for reading. This condition leads to either partial or complete colour blindness and reduced visual acuity (clarity of vision). Most individuals with achromatopsia have no problem with mobility or getting around.

People who have partial colour blindness can have a small degree of colour discrimination, whereas those who have complete colour blindness are only able to distinguish between black, white, shades of grey and often variations in contrast.

Symptoms

The condition is often first noticed in a young child by their parents. Children with achromatopsia may dislike bright lights and often avoid the daylight (known as photophobia). Judging from their behaviour, some parents may notice that their child’s vision may be reduced or blurred. Nystagmus is another symptom of the condition, characterised as involuntary rhythmic eye movements. Symptoms of the condition may be less severe where there is partial recognition of colours.

Causes

Achromatopsia is a genetic condition. Genetic changes or mutations in genes that function in cone cells are responsible for Achromatopsia. To date, mutations in one of five genes are known to cause achromatopsia (CNGA3, CNGB3, GNAT2, ATF6 and NBAS). Of these, two of the most common genes linked to the condition (CNGA3 and CNGB3) account for 75% of achromatopsia cases.

The condition is inherited in an autosomal recessive manner, meaning both copies of a gene don’t work correctly. In this case, the individual’s mother and father have both passed on a mutation in a gene causing Achromatopsia to develop in their child. 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.

Diagnosis

Achromatopsia is diagnosed through a number of tests which are important for providing the correct diagnosis.

The eye doctor will ask about a person’s medical history, including any family history of eye conditions. Individuals will receive a clinical eye examination where they may be asked to read letters off a chart (Snellen chart). They may also check intraocular pressure and examine visual field and visual acuity. Tests for colour vision may also be performed.

An individual may receive a number of imaging tests. Information about the condition may be identified using colour or wide-field fundus photography (which essentially takes photos of the back of the eye). Fundus autofluorescence may be used to identify stress or damage to the retinal pigment epithelium. Optical coherence tomography (OCT) can also be used to assess the various layers at the back of the eye.

An individual may also have an electroretinogram (known as an ERG), which is used to evaluate the functioning of the different types of photoreceptor cells (rods and cones).

A genetic test is also an important component of testing, to ensure the correct condition is diagnosed. In Ireland, this can be performed through the Target 5000 programme.

Genetic Diagnosis

It’s often impossible to tell which type of retinal disease a person has just by looking into the eye. As such, a genetic test may be necessary to confirm the diagnosis.

The Target 5000 programme provides free genetic and clinical testing to all individuals living in Ireland with a genetic retinal degeneration, including Achromatopsia. Through genetic screening of the person awaiting diagnosis and their family members, the Target 5000 programme will provide more detailed information about the nature and inheritance pattern of the condition.

As gene-specific clinical trials and treatments become available, knowing the genetic mutation associated with a genetic retinal degeneration will become even more important. Taking part in this programme ensures participants are included on a national registry from which participants can be identified for clinical trials and treatments and from which further information about each of the genetic retinal degenerations can be defined. For further information on the Target 5000 programme, please contact the Research Department on 01 6789004 or email research@fightingblindness.ie.

Treatment

At present, there is no treatment available for Achromatopsia, however there are significant research efforts underway which aim to change this. To find out more about these advances, please visit the ‘Latest Research’ section.

Maximising the remaining vision that an individual has is a crucial step to take, and there are many low vision aids such as telescopic and magnifying lenses which may be of benefit. The wide range of assistive technologies for people with visual impairments provides plenty of choice for users at all stages of sight loss and this technology has also removed many barriers to education and employment.

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.

General eye check-ups are important for people living with Achromatopsia, as these individuals may still be at risk of developing other kinds of eye problems that affect the general population, some of which may be treatable.

No matter what level of vision a person may have, it is important to look after the eyes. To find out more about what can be done to take care of the eyes on a daily basis, please visit our Tips for Good Eye Health.

For further information, please contact the Research Department on 01 6789004.

Research

Researchers are making advances in understanding this condition in more detail, namely in learning how this condition presents and how it progresses. This work will assist efforts to develop therapeutics to target this condition.

Promising research exists with an aim to develop treatments for achromatopsia, with a major focus on gene therapies. These gene therapies aim to deliver a “normal” copy of the gene which is mutated in this condition into the retina. As two of the genes associated with the condition (CNGA3 and CNGB3) account for 75% of cases, it makes this condition particularly suitable for gene therapy and a number of clinical trials are investigating this.

Information about clinical trials can be found on their website by clicking the following link: Clinical Trials Website and can be searched by condition and trial location.

Fighting Blindness currently support a number of research initiatives which aim to improve the diagnosis, care and quality of life of individuals living with Achromatopsia.

Target 5000 research, largely funded by Fighting Blindness aims to determine the genetic cause and understand the nature of the condition over time. Through Target 5000, a national registry will also be developed which will greatly improve access to suitable clinical trials and treatments for people living in Ireland with Achromatopsia. For further information, please visit (insert link to Target 5000).

Dr Sarah Doyle based in Trinity College Dublin is conducting a study to investigate if a protein known as SARM1 plays a role in retinal degeneration, a key component of Achromatopsia. This work aims to further understand the underlying mechanisms of retinal degeneration and identify potentially new therapeutic targets. To find out more about this study, please visit (insert link to Dr Doyle’s research project).

A study conducted by Professor Breandán Kennedy is investigating a group of neuroprotective drugs, known as HDAC inhibitors, for their potential to delay vision loss in retinal degenerations. This work seeks to identify new therapeutics which could provide significant benefit to individuals. To find out more about this study, please visit (insert link to Prof Kennedy’s research project).

For further information, please contact the Research Department on 01 6789004.

Supports

Receiving a diagnosis can be overwhelming for anyone, but this is not a journey that you have to make alone. There are many groups and resources available to provide support for people living with Achromatopsia.

Fighting Blindness offers a free and confidential counselling service (Insight Counselling). For further information please contact insight@fightingblindness.ie or call 01 6746496.

A mindfulness group is also available on every Wednesday at the Fighting Blindness office at 11am.

For technology support and guidance, the Dublin-based Technology Exchange Club meets every Monday at the Fighting Blindness office at 11am. Another Technology Exchange Club, based in Cork, meet every Saturday in the Cork City Library, Grand Parade, Cork City at 11am. The Cork-based club do not meet on Bank Holiday weekends or on the second Saturday of the month. For further information please contact the following email: insight@fightingblindness.ie or call 01 6746496.

Resources

Féach provides support for parents of children living with sight loss in Ireland.
Click the following link to view their website: Feach Website

ChildVision is the national education centre for children with sight loss in Ireland.
Click the following link to view their website: ChildVision Website

NCBI (National Council for the Blind in Ireland) provides support and services for people living with sight loss in Ireland.
Click the following link to view their website: NCBI Website

Irish Guide Dogs for the blind helps individuals and their families to achieve improved mobility and independence.
Click the following link to view their website: Irish Guide Dogs Website

Last Updated: 4th February 2019