Organisers claim the first one resulted in a massive rise in the number of people being screened for glaucoma, as well as a boost in those getting sight-restoring surgery.

The Lions Club International is co-ordinating events, and will stage its Webcast at an eye hospital it helped found in Nairobi, Kenya, on Thursday at 14.30 GMT.

Ambitious plans

Jim Ervin, the group's president, will announce details of a pledge to save the sight of 20,000 people a week throughout the year 2000, and there will be footage of how travelling eye clinics have helped cataract patients in rural Kenya.

Jimmy Carter will speak to Internet users

And former US president Jimmy Carter will address the Internet audience on the fight against preventable blindness.

The charity estimates that 80% of all blindness is preventable or reversible - with cataracts responsible for half of all cases worldwide.

Cataracts cloud vision until eventually the patient cannot see at all - yet it only takes a simple operation to correct.

Asia and Africa worst hit

Trachoma, glaucoma and river blindness are among other significant causes of vision loss, and the World Sight Day organisers want to educate people on how to spot warning signs and get treatment.

In particular, they want to raise awareness of problems in Africa and Asia - where most of the world's cases of blindness occur.

Mr Ervin said: "One of the reasons we selected Kenya as the primary location for World Sight Day is that nearly 80% of the world's blind live in Asia and Africa."

"Last year's events on five continents were very much a success, with 600,000 extra glaucoma screenings and 20,000 additional corneal transplants since then," a spokesman for Lions Club International said.

"And awareness of preventable blindness has shot up."