A link between glaucoma and Alzheimer's has been discovered that could lead to the eye condition being seen as an early warning for dementia.

Scientists established a "clear link" between the causes of Alzheimer's and "one of the basic mechanisms behind glaucoma".

Due to glaucoma's tendency to develop several years before Alzheimer's, the presence of the eye disease may provide a warning for doctors when treating elderly patients.

Dr Francesca Cordeiro, a glaucoma specialist at the Western Eye Hospital in London, said there was increasing evidence of a link, noting that the normal occurrence of glaucoma is 1.8 per cent, while one study found it to be at least 25 per cent in Alzheimer's sufferers.

The findings could speed up the development of treatments for Alzheimer's as well as revolutionising the treatment of glaucoma, the most common cause of blindness.

Most of the 600,000 glaucoma sufferers in Britain are over 40. People with the disease lose their wider field of vision, often without realising that their sight is deteriorating.

Alzheimer's disease affects 420,000 people in Britain and is responsible for two-thirds of all cases of dementia. The majority of people with Alzheimer's are over 65.