The greatest fear of patients with eye disease is going “blind.” While there are a number of eye diseases that can lead to some form of vision impairment (less than normal vision), they can affect different aspects of vision and patients can often adapt by using their remaining vision.
Absolute blindness, called “no light perception,” is when a person can’t tell the difference between light and dark, even when a bright light is shined into his/her eyes. This condition is rare. Assistance from the government and foundations is available for these persons.
Legal blindness is defined in the United States as best corrected visual acuity (with glasses) of 20/200 or less in the better eye, and/or a visual field of 20 degrees or less. Legally blind patients qualify for benefits from the government. People with legal blindness may still have some usable vision
Age-Related Macular Degeneration
Legal blindness can be caused by age-related macular degeneration (AMD) because this disease affects the central vision provided by the macula (the specialized central part of the retina). Patients with severely damaged maculas in both eyes have visual acuity measured on an eye chart of 20/200 or worse. However, their peripheral, or side vision is usually intact, so they can see shapes and movement, and read large letters with the help of magnification and bright lights.
Patients with AMD can decrease their risk of legal blindness by stopping smoking, eating vegetables, fruits (every day), and salmon or sardines (twice a week), and, in some patients, by taking the AREDS formula antioxidant vitamins. Also, medicines can be injected into the eye in patients with wet AMD to help slow or stop vision loss.
Rare genetic diseases affecting the retina can also cause legal blindness. For example, retinitis pigmentosa can cause “tunnel vision,” in which only a tiny window of central vision remains. Such patients might be able to read 20/20 size letters, but would be legally blind because of the small visual field. Retinal gene therapy developed at the Scheie Eye Institute at the University of Pennsylvania has recently been FDA approved for one form of the hereditary retinal disease called Leber’s congenital amaurosis. The treatment works by injecting normal copies of the RPE65 gene into the retinas of patients born with mutations in this gene. It is expected that additional research will lead to gene therapy for other forms of hereditary and acquired eye diseases.
Another retinal disease that can cause legal blindness is diabetic retinopathy. Patients with diabetes can lose vision from swelling or bleeding in the retina, or from retinal detachment. Diabetics can decrease their risk of legal blindness with good blood sugar and blood pressure control and annual eye exams.
Legal blindness can also be caused by glaucoma, a disease in which the retinal neurons that send the signal from the eye to the brain die. This disease most often progresses slowly over time, with patients losing part of their visual field and/or visual acuity. If the visual field diminishes to 20 degrees or less, then the patient is legally blind. The normal binocular visual field (using both eyes) in the horizontal plane is about 180 degrees. Progression of visual field loss can usually be slowed or stopped by lowering the eye pressure with medications and/or surgery. The earlier the diagnosis and treatment, the better, to preserve your sight.
Severe cataract, or clouding of the lens can cause visual acuity to drop to 20/200 or less because the cataract does not permit enough light to reach the retina in the back of the eye. Fortunately, cataracts can be surgically removed and the cloudy lens replaced with a clear plastic one, usually resulting in significantly improved vision.
- Macular Degeneration Toolkit (Helpful Information to Understand and Manage Macular Degeneration)
- Expert Information on Macular Degeneration (Articles)
- BrightFocus Chats (Audio Presentations on Macular Degeneration)
- Macular Degeneration Research News (Newsletters)
- Glaucoma Toolkit (Information to Help You Understand and Manage Glaucoma)
- Expert Information on Glaucoma (Articles)
- Macular Degeneration: Essential Facts (Publication)
- Glaucoma: Essential Facts (Publication)
- Government Benefits for Macular Degeneration (Resource List)
- Government Benefits for Glaucoma (Resource List)
This content was last updated on: December 3, 2019
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