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Cone-Rod dystrophy is a group of rare and inherited retinal degenerations (IRDs) which affect the light-sensing rod and cone photoreceptor cells in the retina, the tissue layer which lines the back of the eye.
Cone cells are most concentrated at the centre of the retina, in the macula. They perceive bright light, facilitate central vision and are required for daily tasks, such as reading and driving. Rod cells exist primarily around the outer edges of the retina for peripheral vision. They also perceive dim light and help with night vision.
In contrast to Retinitis Pigmentosa, which results from the loss of rod cells, followed by the cone cells, Cone-Rod dystrophy occurs in the opposite way, where cone cells are the first photoreceptor cells affected, followed by loss of rod cell function.
What are the symptoms of cone rod dystrophy?
A reduction in visual acuity and increased light-sensitivity (photophobia) are common early symptoms of Cone-Rod dystrophy, while blind spots also develop in central and peripheral vision, due to degeneration of the cone cells. As the rod cells begin to die, people living with Cone-Rod dystrophy begin to experience night blindness and reduced peripheral vision. The level of vision loss and rate of disease progression varies considerably between each person living with the condition and is therefore very difficult to predict what an individual’s vision will be like at a specific time in the future. Some forms of Cone-Rod dystrophy are inherited; other forms appear to occur spontaneously for no apparent reason (sporadically).
Cone-Rod dystrophies have many similarities to RP following varied inheritance patterns, including autosomal dominant, autosomal recessive, and X-linked modes of transmission. You can read more about these inheritance patterns in our Genetics and Inheritance section.
What Causes Cone-Rod Dystrophy?
Cone-Rod dystrophy is most commonly caused by a mutation in the ABCA4 gene. Cone-Rod dystrophy caused by the ABCA4 gene has an autosomal recessive pattern of inheritance, which means that two faulty copies of the ABCA4 gene are required for the condition to develop. Cone-Rod dystrophy is most frequently inherited through an autosomal recessive pattern, although an autosomal dominant and X-linked form of the disease also exists, and in rare cases, cause Cone-Rod dystrophy.
More than 30 genes are associated with Cone-Rod dystrophy and have a key role in ensuring the correct structure and function of the light-sensitive rod and cone photoreceptor cells. As the name suggests, cone cells are the first to degenerate, followed by the rod cells and is evident in central and colour vision loss as early indicators of the condition.
What treatments are available?
Currently, there are no treatments available for people living with Cone-Rod dystrophies to prevent vision loss. However, low-vision aids, such as telescopic and magnifying glasses help to maximise an individual’s remaining vision.
Eye exams like electroretinograms are used to check for cone-rod dystrophy by assessing photoreceptor cells in the back of the eye and although Cone-Rod dystrophy can’t be treated, other retinal conditions with therapies can be diagnosed. Regular visits to your eye doctor can also make you aware of current advances as we learn more about these conditions.