The World Health Organisation has warned that the number of people who go blind will double in the next 20 years unless urgent action is taken.

The WHO is launching a global initiative to combat what it calls "avoidable blindness" by the year 2020.

Claire Doole in Geneva: Every five seconds someone goes blind

The organisation estimates that many of the 45m people worldwide who are blind could be treated.

Every five seconds someone goes blind somewhere in the world, and 180m people are visually disabled.

Of those, 45m have lost their sight, but nine out of 10 of them live in the developing world, where poverty is not only often a cause of blindness, but also an obstacle to treatment.

The World Health Organisation estimates 80% of the cases could be avoided by increasing the number of cataract operations performed, as well as by stepping up efforts against eye diseases, such as trachoma and glaucoma.

But the WHO has neither time nor money on its side, fearing that the world's blind population is getting bigger.

The head of the WHO's Disability Unit, Dr Bjorn Thylefors, says urgent action is needed.

"We see the next generation, the next couple of decades, as particularly critical because we have to start now to stop this trend," says Mr Thylefors.

The WHO's Right to Sight campaign aims to tackle the problem of avoidable blindness by working in partnership with other agencies in some of the worst affected regions, such as sub-Saharan Africa and South Asia.