An international study led by King's College London has identified genetic links to glaucoma, an eye condition that can lead to blindness and visual impairment.

Glaucoma is the leading cause of irreversible blindness in the world and results from damage to the optic nerve, usually due to pressure inside the eye (intraocular pressure) being too high, as the eye fluid does not drain properly.

The study, published in Nature Genetics and funded by the Wellcome Trust and Fight for Sight, the main UK charity that funds pioneering eye research to prevent sight loss and treat eye disease, could lead to earlier diagnosis and new therapies for treating the condition. Researchers carried out a meta-analysis of more than 35,000 people from seven countries, including subjects of Asian and European descent, with data drawn from the International Glaucoma Genetics Consortium (IGGC).

They found four new genes associated with high eye pressure and glaucoma. One of the genes is the ABO gene, which determines blood group, and higher eye pressure appears to be linked to blood group B.

The study also found that a genetic change in the ABCA1 gene is associated with an increased risk of developing both high inner eye pressure and glaucoma. ABCA1 is a major regulator of cellular cholesterol and lipid levels, although further research is required to understand how this mechanism works in the eye. Interestingly two other studies from Australia and China found ABCA1 to be linked to glaucoma, also published in Nature Genetics.

Early diagnosis of glaucoma is crucial because, if treated early enough, damage to vision can be prevented. In future it may be possible to provide intensive screening to those identified as being at higher genetic risk.

Treatments could be targeted at reducing the amount of ABCA1 in the eye either by using chemicals to block the proteins produced by the gene or by altering the gene's expression. This would serve to decrease the degree of pressure it creates on the optic nerve and nerve fibres from the retina.

Professor Chris Hammond from the Department of Twin Research and Genetic Epidemiology at King's College London, who directed the study, said: 'Although eyedrops are already available to treat glaucoma, these are not always effective. Our findings help us to understand why some people get glaucoma and explain why the condition tends to run in families.'

Dr Pirro Hysi, also of King's College London and lead author of the study, said: 'For the first time we have established a link between this disease and genes that regulate cholesterol metabolism as well as cause atherosclerosis and other age-related diseases. This new knowledge makes us hopeful that more effective treatments for glaucoma will be available in the not so distant future.'