An estimated 135 million people havelow vision（近视）. Forty to forty-five million others cannot see at all. Health experts warn that the number of blind people will increase sharply as the world population grows, and grows older. They say the number of blind people could almost double by 2020.

Yet the World Health Organization says that in eight out of ten cases, blindness can be cured or avoided.

October ninth was World Sight Day. A campaign called Vision Twenty-twenty released materials to help governments and health workers develop national plans to prevent blindness.

Vision Twenty-twenty is a joint effort of the W-H-O and the International Agency for the Prevention of Blindness. The goal is to endpreventable（可预防的）blindness by 2020. The campaign targets four main causes.

Cataracts（白内障）cause thelens（晶状体）of the eye to becomecloudy（模糊不清的）. In most of Africa and Asia, cataracts cause at least half the cases of blindness that can be cured. A simple operation can remove cataracts.

Trachoma（沙眼）is an infectious disease spread person-to-person and by insects. Trachoma causes about fifteen percent of all cases of blindness. Most of the cases are in Africa. The disease can be treated with antibiotic medicines and an operation to correct the damage.

The disease known asriver blindness（河忙）is also found mostly in Africa. Flies spread the infection. A yearly treatment of the drug Mectizan can control the disease.

Finally, a lack of vitamin A as a result of poor nutrition is the leading cause of preventable blindness in children.

Vision Twenty-twenty says that every five seconds another person in the world goes blind. Most blind people live in developing nations. India has at least nine million. About six million are in China, and seven million in Africa.

Officials estimate that the world economy loses about twenty-eight-thousand-million dollars each year from curable blindness.

A resolution passed by the World Health Assembly in May urges all governments to develop national plans to prevent blindness. You can learn more about Vision Twenty-twenty on the Internet at v-twenty-twenty dot o-r-g.

This VOA Special English Development Report was written by Jill Moss.