Causes of blindness and low vision
Around the world, 285 million people are visually impaired; 39 million are blind and 246 million have low vision. Global estimates show that without intervention, the number of blind will increase to 76 million by the year 2020. This represents one of the most serious health issues facing the world today. Blindness affects not only individuals and their families, but whole communities as well. But there is good news – 80 percent of blindness in the developing world can be successfully treated or prevented.
A cataract is a clouding of the lens of the eye. The lens is located near the front of the eye and it focuses on the retina, at the back of the eye, to form the image we see. A cataract may cloud the entire lens, or affect just a small part.
Trachoma is the world's leading cause of preventable blindness. Caused by bacterial infection, trachoma spreads easily through contact with eye discharge from infected people on hands, towels and clothing, and through direct transmission by flies.
Glaucoma is the leading cause of blindness in North America. More than 2.2 million people over the age of 40 have glaucoma, while half as many again may be unaware they have this potentially blinding disease because they have no symptoms.
Onchocerciasis is often called "river blindness" and occurs in central Africa and central America near flowing rivers and streams, where the species of black flies that transmits the disease is most often found. Bacteria from the fly allow parasitic worms carried by the flies to enter a person's bloodstream, where the worms can live for up to 14 years. Symptoms of river blindness often show up one to three months after the infection.
Low vision due to refractive error is the most common form of visual impairment. For people who cannot afford the services of an optometrist, seeing poorly is almost as bad as not being able to see at all.