Thousands of Scots could be suffering progressive loss of sight without realising it, a charity is warning as World Glaucoma Week starts on Sunday, March 12.

Glaucoma is the second largest cause of registered blindness in the UK but it is estimated almost half of those affected don't know they have it.

Around 3,700 people across Ayrshire have been diagnosed with the condition, and 52,000 across Scotland.

RNIB Scotland director Campbell Chalmers said: "Glaucoma has been nicknamed 'the sneak-thief of sight' because its effects are usually unnoticeable until a relatively advanced stage. By then the damage is done. Glaucoma doesn't have any symptoms in its early stages so people can lose up to 40 per cent of their sight before they realise they have a problem.

"We need to ensure that people are diagnosed early so that they do not reach the stage where sight loss is irreversible."

Glaucoma is the name for a group of eye conditions in which increased pressure within the eye squeezes the optic nerve and damages some of the nerve fibres. This nerve carries information from the retina (the light sensitive layer in the eye) to the brain where it is perceived as a picture. Peripheral vision is the first area to be affected. But if glaucoma is left untreated, the damage can lead to eventual loss of central vision.

Regular eye tests can pick up signs of the condition before any damage has occurred, maximising the chances of successful treatment. Some people are more at risk than others: those aged over 40, those of African and African/Caribbean origin, those with a family history of glaucoma, people with very short sight (severe myopia), and diabetics.

"Regular eye tests, which are free in Scotland, are vital if glaucoma is to be detected early and sight loss prevented," emphasised Mr Chalmers.

"Adults should have an eye test every two years. People over the age of 60 should have an annual eye test as should those over the age of 40 from higher risk groups. Since glaucoma is associated with advancing age, the number of patients requiring management of the condition is rising as life expectancy increases."

Glaucoma facts: 

There are two main types of glaucoma - chronic and acute. The optic nerve of the eye is damaged, often as a result of raised eye pressure.

Glaucoma damages the peripheral vision first and up to 40 percent of your sight may be lost before you notice a difference.

An eye test is the only way to detect glaucoma in its early stages.

Advanced cases of glaucoma can result in tunnel vision so that you may be able to recognise a face in front of you but not notice someone standing beside you.

African-Caribbean people, those with a close relative with glaucoma and older people are at a much higher risk of developing chronic glaucoma.

If caught early enough glaucoma can, in nearly all cases, be successfully treated and no sight need be lost.