Twin brothers Michael and Daniel Smith on losing sight

Twin brothers Michael and Daniel Smith have an extremely rare condition for which there is no known cause or cure.

Leber's Optic Neuropathy is the loss of vision as a result of the death of cells in the optic nerve, causing it to stop relaying vital information from the eyes to the brain.

Although it is a hereditary condition, linked to a number of genes, the brothers have been unable to find any family history going back four generations.

Only 150 people in the UK are known to be affected by the condition, with around 95 per cent never returning to full-time education.

The twins though are determined to continue studying, and they are also preparing to cycle from London to Amsterdam.