The choroid part of the eye is essential in providing the spherical surfaces of the eye with blood and oxygen – it is a “vascular” layer, meaning it contains a network of blood vessels and capillaries.
The outside white part of the eye known as the sclera and the inside retinal layer which senses light focussed by the eye lens, are formed either side of the choroid so that they can both be fully nourished.
Also known as the choroidea or choroidal layer, the choroid can be subject to a variety of diseases and disorders:
Choroiditis and chorioretinitis, with the suffixes “itis”, indicate that they are inflammation type diseases.
Disorders of the choroid include the general classification of hereditary choroidal dystrophy of which choroideremia is part. As the name suggests these disorders are characterised by the way in which they are passed on from parents. Dystrophy describes the condition whereby parts of the body develop abnormally and slowly degenerate, as in muscular dystrophy for example.
What is Choroideremia?
Choroideremia, often designated using the acronym CHM for short, describes the process of the blood vessels and capillaries in the choroid slowly degenerating to the extent that the parts of the eye relying on them – the sclera and the retina – also degenerate and vision is gradually lost. Some eye professional use the term “choroidal sclerosis” in respect of hardening and degeneration.
Who gets it?
Only males get choroideremia; if females do exhibit the condition it is usually very mild and no real effects are experienced.
The disorder is inherited through an X-linked pattern – that is to say a male who is affected passes on the mutation to all female children, but not to male children. The female in this instance becomes a carrier and there is a 50% chance that she will pass on the mutation to her children.
The occurrence of the disorder is quite rare – only 10 to 20 males per million of the population are likely to have it.
What are the symptoms?
The symptoms are slight at first before slowly progressing:
• Poor night vision especially when compared to peers when in the teens
• Decreased width of vision – a large peripheral “blind spot” may begin to be noticeable and “tunnel vision” gradually takes over. Lack of colour perception might begin to happen.
• In later adult years serious vision loss may result leading to blindness
Can choroideremia be detected early, and what then can be done about it?
There is a genetic test that can be carried out through a blood sample to diagnose choroideremia. A great deal of work has been carried out and is currently underway at the University of Alberta in Canada.
The most promising research in dealing with and treating choroideremia is in the area of gene therapy, and pre-clinical trials are being conducted.
In the meantime, a management process rather than treatment regime is the order of the day.
Improved nutrition and added vitamin supplementation, the wearing of UV-blocking sunglasses and consultations with specialists in the area of low vision are all actions that can be taken.