Legal blindness is a term that applies to people with a specific threshold of visual impairment (20/200 vision). Notably, legal blindness is not the same as total blindness where a person cannot see anything at all. A legally blind person can have some vision and may be able to see things like shapes and colors. Legal blindness can be the result of accidents or eye disorders, including Cataracts and Age-related Macular Degeneration. Those who are legally blind may qualify for disability benefits, such as those offered by the Social Security Administration in the United States. Various government agencies and non-governmental organizations offer benefits and aid as well, which can include low visibility aids and other tools or assets to help improve daily functioning. The visual impairment must be medically reviewed and validated by an optometrist or other physician for the person to receive benefits.
What Does Legally Blind Mean?
Due to legal blindness being a legal term rather than a medical one, its definition can vary according to location. For example, the United States, Canada, and the United Kingdom define legal blindness as having corrected vision of 20/200 in the individual’s best eye with the help of contact lenses or glasses. Having 20/200 vision means the person cannot be more than 20 feet (six meters) away to see what someone with normal vision can see at 200 feet (60 m).
Visual Acuity – What Is the Prescription of Legal Blindness?
A visual acuity exam is an eye exam that tests a person’s ability to identify the shapes and details of objects presented. Visual acuity is expressed as a fraction. A person with normal vision will have visual acuity of 20/20. A person is considered legally blind if a visual impairment limits vision to 20/200 or one-tenth of normal vision.
Some government agencies also consider the visual field to determine legal blindness. The visual field is the entire area a person can see, including their peripheral vision, when looking straight ahead. Eye doctors express visual field in terms of degrees, with the normal visual field of each eye spanning more than 120 degrees horizontally and 90 degrees vertically. Someone who has a visual field of 20 degrees or less, even with the help of glasses or contacts, is considered legally blind in some countries. This is also referred to as “tunnel vision”, which means the individual has trouble seeing objects on the left and right sides of their body when looking straight ahead.
Legal Blindness vs. Low Vision vs. Total Blindness
Although the terms “low vision”, “legal blindness”, and “total blindness” may seem similar, they describe different things. Optometrists and government agencies usually define legal blindness as someone having 20/200 vision in the best eye, even with glasses or contacts, indicating a substantial deficit in vision.
Low vision, on the other hand, is defined as having 20/70 vision in the best eye with glasses or contacts. While low vision can interfere with daily activities, the vision loss is not quite as profound as legal blindness.
Total blindness describes a complete lack of light and form perception. In other words, people who are totally blind cannot see any light and cannot make out the form of anything in front of them. Total blindness is rare – 85 percent of those with eye disorders have some remaining sight, meaning only about 15 percent of people with an eye disorder experience total blindness.
Legal blindness does not mean someone cannot see anything at all. In fact, most legally blind people retain some vision. They might be able to see objects right in front of them but not to the sides (tunnel vision). Or, they might have good peripheral vision but have trouble seeing objects right in front of them (central vision loss). Most of the time, legally blind people have their field of vision so narrow or blurry that it makes everyday activities difficult to perform. Some people also have blind spots that cannot be corrected with glasses or contact lenses.
Blind spots and narrowed or blurred vision
Associated with legal blindness, these are the results of defects or damage in various eye tissues. The eye is a complex organ, and even the smallest amount of tissue damage can have a significant effect on vision.
There are many causes of legal blindness, including accidents, injuries, and eye disorders. The four leading causes of legal blindness are eye disorders, namely Age-related Macular Degeneration, Cataracts, Diabetic Retinopathy, and Glaucoma.
Age- Related Macular Degeneration
Age-related Macular Degeneration (AMD) is a leading cause of vision loss in Americans aged 60 and older. Macular Degeneration (MD) is progressive and results from the deterioration of the macula (the central portion of the retina). The macula is responsible for the sharp, central vision needed for reading, driving, cooking, and other activities of daily life.
Diabetic Retinopathy is the most common cause of vision impairment among adults in the United States. The condition develops exclusively in people with diabetes. In cases of Diabetic Retinopathy, high blood sugar causes changes to the blood vessels serving the retina such that the vessels swell and leak or close off completely. Ultimately, oxygen-rich blood is prevented from reaching the retina. In advanced Diabetic Retinopathy, abnormal blood vessels also grow on the retina.
Cataracts are cloudy areas on the eye’s lens, which prevent sufficient light from reaching the retina in the back of the eye, resulting in impaired vision.
Glaucoma accounts for 9 to 12 percent of all cases of blindness and is characterized by high pressure within the eyeball. Consistent high-intraocular pressure can damage the optic nerve and result in visual impairment.
An optometrist can diagnose if a person is legally blind through a standard eye exam, using the Snellen Chart – the standard for measuring eyesight clarity in the United States. Measurement of visual acuity and/or visual field can help determine if someone is legally blind.
Various treatment options are available for people with legal blindness depending on the cause of their visual impairment. However, in some cases — such as retinal degeneration disorders, symptoms can be managed but there is no existing cure.
Some causes of visual impairment that can be treated include:
- Diabetic Retinopathy: Although no treatment can resolve existing damage, worsening of the condition can be prevented by receiving injections, laser treatment, or eye surgery.
- Age-Related Macular Degeneration: If a person has dry AMD, there is no available treatment. However, if a person has wet AMD, treatments may involve receiving regular injections or photodynamic therapy.
- Cataracts: A person with severe Cataracts may require surgery to restore vision.
- Glaucoma: Although the damage caused by Glaucoma cannot be reversed, treatment and regular checkups can help reduce or even stop loss of vision. Treatment options include lowering intraocular pressure through medication, eye drops, laser treatment, surgery, or a combination of these, depending on the severity.