Last Reviewed June 2, 2009
Symptoms & Characteristics
In the United States, a person is considered legally blind if their visual acuity is 20/200 or worse in the better eye with best correction, or their field of vision is 20 degrees or less (tunnel vision) in the better eye. Visual acuity of 20/200 means that a person at 20 feet from an eye chart can see what a person with normal vision can see at 200 feet.
Treatment
Treatment availability is dependent upon the cause of blindness.
How Common Is It?
More than 1 million people in the United States are considered legally blind.
Genetics & Inheritance
Blindness can be acquired, multifactorial (caused by a combination of genetic and environmental factors) or caused by a inherited genetic condition or defect. Some causes of blindness include:
Eye injury (Acquired)
Although less than 4% of all cases of blindness are caused by injury, it is the most common cause of monocular blindness (vision loss in one eye only).
Malnutrition and Vitamin Deficiencies (Typically Acquired)
Vitamin A deficiency is associated with vision loss but is uncommon in the United States.
Eye Disease (Acquired, Multifactorial or in some cases Inherited)
Most cases of blindness in the United States are caused by eye disease. Some of the more common types of eye disease associated with blindness include:
- cataracts (involve clouding of the lens)
- glaucoma (involves progressive damage to the optic nerve from too much pressure in the eye)
- uveitis (involves inflammation of tissue in the middle layer of the eye)
- trachoma (an infectious eye disease)
- corneal disease (damage to the cornea)
- diabetic retinopathy (involves damage to the small blood vessels in the retina)
Poisoning (Acquired)
In rare cases, blindness is caused by the intake of certain chemicals, such as methanol.
Genetic Conditions (Inherited)
There are numerous genetic conditions that are either associated with congenital blindness, eye abnormalities and/or progressive blindness. Many of these conditions are also associated with deafness. Some of the more common genetic conditions associated with blindness include:
- Retinitis Pigmentosa (RP) is a group of hereditary conditions in which the light-sensitive tissue at the back of the eye (the retina) gradually deteriorates. RP is one of the most common causes of hereditary blindness.
- Usher syndrome causes hearing loss and vision loss. Vision loss is primarily caused by retinitis pigmentosa.
- Norrie disease causes abnormal development of the retina and leads to blindness in male infants at birth or soon after birth.
- Alström syndrome affects many body systems and is associated with progressive loss of vision and hearing.
- Stickler syndrome is a group of hereditary conditions characterized by a distinctive facial appearance, eye abnormalities, hearing loss, and joint problems.
- Choroideremia is characterized by progressive vision loss caused by degeneration of the choroid and retina (parts of the eye). This condition mainly affects males, but affected females have also been reported.
- Lowe syndrome primarily affects the eyes, brain, and kidneys. This condition mainly affects males.
- Lenz microphthalmia syndrome is characterized by abnormal development of the eyes and several other parts of the body. This condition mainly affects males.
- Oculocutaneous albinism is a defect in the production or distribution of melanin, which results in the partial of full absence of coloring (pigmentation) of the skin, hair, and eyes. Ocular albinism primarily affects the eyes.
- Aniridia is characterized by a complete (or partial) lack of development of the iris (the colored part of the eye). Aniridia can be associated with other ocular defects or physical defects.
An evaluation by a medical geneticist may be helpful in establishing cause. This is not only important for the health and management of the affected person but also for an accurate estimation of recurrence risk within a family.
Genetic Testing
Clinical genetic testing for some of the genetic conditions and eye diseases associated with blindness may be available through an in person genetic consultation for people who are considered at risk. For more information on genetic causes of blindness, accurate diagnosis, and recurrence risk; use our find a genetic professional directory to locate a trained
genetic professional in your area.
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