Blue Cone Monochromacy


Blue Cone Monochromacy (BCM) is a rare (1:100,000) genetic X-linked retinal degeneration. It is recognised by severely impaired colour discrimination along with additional visual problems including low visual acuity and nystagmus. 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. There are three types of cones cells that respond to one of three colours: red, green and blue. People with blue cone monochromacy do not have functioning red and green cones while the blue cones work normally. This condition results in reduced visual acuity and impaired colour discrimination. Most individuals with BCM have no problem with mobility.


The condition is often first noticed in a young child by their parents. BCM predominantly affects males. Children with BCM 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. Nystagmus may decrease over time.


Blue cone monochromacy is a genetic condition. Genetic changes or mutations in genes that function in red and green cone cells are responsible for BCM. To date, mutations in two genes are known to cause BCM, OPN1LW and OPN1MW. The condition is inherited in an X-linked recessive manner, meaning the disease causing copy of a gene is found on the X chromosome. In this case, the individual’s mother has passed on a mutation in a gene causing BCM to develop in their child. Most often, the mother of an individual with BCM carries one copy of the mutated gene, but do not show signs and symptoms of the condition. Usually, those affected are male, but BCM can rarely be found in females. More information about inheritance patterns can be found at our Genetic Inheritance section, or,  please contact the Research Department on 01 6789004 or e-mail


BCM 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 an inherited retinal degeneration, including BCM. 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 an inherited 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 inherited retinal degenerations can be defined. For further information on the Target 5000 programme, please contact the Research Department on 01 6789004 or email


At present, there is no treatment available for BCM, 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 BCM is worse in bright light. Some people with BCM might benefit from tinted lenses which may reduce glare and maximise vision in brighter light conditions. General eye check-ups are important for people living with BCM, 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.


Great advances have been made with respect to understanding this condition, with much progress being made to develop therapies for it. Promising research exists with an aim to develop treatments for BCM, 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 only two genes are associated with the condition, OPN1LW and OPN1MW, it makes this condition particularly suitable for gene therapy and a number of research efforts are investigating this. 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 has been developed which greatly improves access to suitable clinical trials and treatments for people living in Ireland with BCM and othe inherited retinal degenerations. For further information, please contact the Research Department on 01 6789004 or e-mail A study conducted by Fighting Blindness researcher 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. More information about clinical trials can be found on the clinical trials website, and searched by condition or location. To find out more about these studies, please contact the Research Department on 01 6789004 or e-mail


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 Stargardt Disease. Fighting Blindness offers a free and confidential counselling service (Insight Counselling). For further information please contact or call 01 6746496. We also offer support groups for people with a visual impairment to share their feelings and experiences with others facing the same challenges. Please consult the support groups section of our website here to access the latest timings and days for the various support groups we offer. For further information please contact or call 01 6746496.


BCM Families Foundation is dedicated to elevating public understanding surrounding this rare disease as well supporting innovative research. They have also established the BCM Registry, an online patient registry dedicated to Blue Cone Monochromacy. Féach provides support for parents of children living with sight loss in Ireland. ChildVision is the national education centre for children with sight loss in Ireland. Vision Ireland, formerly NCBI (National Council for the Blind in Ireland) provides support and services for people living with sight loss in Ireland.