Blindness

What Causes Blindness?

Many conditions may cause blindness. The most common cause of vision loss in infants and young children is amblyopia (am-ble-O-pe-a).

^*strabismus is a condition that causes the eyes to cross or not work together correctly, which may lead to permanent loss of vision in one eye.

^*glaucoma is a group of disorders that cause pressure to build in the eye, which may result in vision loss.

^*cataracts result from cloudiness of the lenses in the eyes that usually develops as a person ages. They often impair vision.

Amblyopia

Amblyopia is the loss of vision in one eye that results when the eyes are misaligned or not working together correctly in a condition known as strabismus (stra-BIZ-mus). About 3 to 5 percent of children have strabismus, which usually is present from birth or develops during infancy. In most cases, there is no known cause for the condition, which often makes a person look cross-eyed. With early diagnosis and treatment,

Anatomy of the eye. The optic nerve (also referred to as the second cranial nerve) sends messages from the eyes to the brain, making it possible to see.

the eye that is not pointing straight can be trained to develop normal vision. For some people, surgery is needed to align the eye correctly.

Cataracts

Some children are born with cataracts, which cloud the lens in the eye and prevent images from being seen clearly or at all. People also develop cataracts as they age, which makes it one of the most common causes of reduced vision. More than 400,000 new cases of cataracts develop each year in the United States. Surgery to remove cataracts is common for adults and for those few children with them. This restores vision in more than 90 percent of cases.

Diabetes

Diabetes may lead to vision loss if diabetic retinopathy develops. Diabetic retinopathy, one of the leading causes of blindness in adults, results in vision loss if blood vessels supplying the eye's retina^* are damaged by the disease. The blood vessels sometimes leak or break open to damage the retina. More vessels also may grow and start to cover the retina or grow into the fluid that fills the eyeball, further reducing vision.

Researchers estimate that as many as 10 million to 15 million people have diabetes in the United States and 700,000 are at risk of developing diabetic retinopathy. Almost all people with diabetes can show signs of damage to their retina after two or three decades of living with the disease, but not all of them lose their vision. There are no symptoms of diabetic retinopathy at first. As the damage increases, vision becomes blurred. Doctors can see the damage with a device that looks at the retina, which is why annual vision exams are so important for people with diabetes.

The best treatment for diabetic retinopathy is prevention, which means managing diabetes (and high blood pressure, if present) with proper nutrition, exercise, and medications. In some cases, laser treatment may be used to prevent worsening of diabetic retinopathy. People with diabetes also are at higher risk for cataracts and glaucoma.

Glaucoma

Glaucoma is a disorder that causes fluid pressure to build up inside the eye, which may cause optic nerve^* damage. It may go undetected for many years before its effects on vision are noticed. It is one of the leading causes of blindness in the United States, with elderly people and people of African ancestry at increased risk.

Trachoma

Trachoma is a chronic infection of the eye by Chlamydia trachomatis bacteria. The bacteria infect the linings of the eyelid, causing them to become thick and rough. If the condition is untreated or if the infection returns, the eyelashes can turn inward and cause small scars on the eyes' surfaces. Eventually, blindness results. Trachoma is the leading cause of preventable blindness in the world.

Trachoma is spread through contact with the discharge from the eyes of infected persons. For example, if infected people rub their eyes and then shake another person's hands, the bacteria that cause trachoma can be spread. Also, using the handkerchief or towel of an infected person can spread the bacteria.

Today, about 10 percent of the world's population live in areas where trachoma is a problem, including Africa, Asia, Australia, Latin America, and some poorer areas of the United States.

Treatment can stop trachoma before it blinds people. Antibiotic ointments or oral antibiotics are used to treat the disease. The World Health Organization (WHO) has established a WHO Alliance for the Global Elimination of Trachoma. WHO hopes to achieve its goal by the year 2020 through prevention, antibiotics, and surgery to repair eyelids.

^*retina is the area at the inside rear of the eyeball that acts like film in a camera to capture the image a person sees.

^*optic nerve is the nerve that sends messages, or conducts impulses, from the eyes to the brain, making it possible to see. The optic nerve is also referred to as the second cranial nerve.

Macular degeneration

Macular degeneration is similar to diabetic retinopathy. Changes in the blood vessels supplying the central portion of the retina, known as the macula, cause the vessels to leak and to damage cells that are needed for the central part of the field of vision. Peripheral or side vision usually remains, but without treatment, the damaged field of vision may expand. Doctors sometimes recommend laser surgery to treat the leaking blood vessels when people are in the early stages of macular degeneration in order to prevent or slow progressive vision loss. Others compensate for vision loss by using magnifying devices.

Infections

Ocular (OK-yoo-lar) herpes may cause vision loss as a result of herpesvirus infections, usually the herpes simplex virus that causes cold sores or the herpes zoster virus that causes chickenpox and shingles. The U.S. National Eye Institute estimates that ocular herpes affects approximately 400,000 people in the United States.

Infection of the eyes by the Chlamydia trachomatis organism is a leading cause of blindness in developing nations. The eyes of newborn babies may become infected during childbirth if the mother has chlamydia.

Accidents

About 3 percent of cases of blindness occur from accidents or other injuries that damage the eyes.

How Do People with Vision Loss and Blindness Adapt?

Millions of people with severe vision loss, including more than 1 million people who are blind, can do many of the same things that people with normal vision do. People with partial sight can use powerful eyeglasses and magnifying devices to improve their ability to read and to see objects. People with blindness also can:

• listen to books, newspapers, and magazines on tape
• use computers that read text aloud and respond to spoken commands
• read Braille, a system that translates words into raised patterns of dots that are read by touching them
• use guide dogs to increase their mobility
• take many of the same classes, jobs, and roles as people with sight
• become parents and teachers