Malcolm Rivera
Legal blindness is a specific status set by government agencies and organisations to determine eligibility for benefits and services. It is not a medical term but a guideline. In the United States, a person is legally blind if they meet at least one of the following criteria: a central visual acuity of 20/200 or worse in the better eye with correction, or a visual field of 20 degrees or less in the better eye. This means that a legally blind person's vision is impaired to the extent that they are unable to drive and may struggle with mobility, employment, and daily tasks. It is important to note that most people who are legally blind have some usable vision, unlike complete blindness, and can see some level of light.
| Characteristics | Values |
|---|---|
| Legal definition | "Legally blind" is a specific status set by government agencies. It is not a medical term but a guideline. |
| Visual acuity | 20/200 or worse in the better eye with corrective lenses. |
| Field of view | No more than 20 degrees wide in the better eye. |
| Peripheral vision | Limited or no peripheral vision. |
| Prevalence | More than 3.3 million people over age 40 are legally blind or have low vision in the US. |
| Benefits and services | Legal blindness is used to establish eligibility for federal, state, local, and institutional benefits and services, including financial aid for assistive technologies, guide dogs, etc. |
| Remaining vision | About 80% of individuals who are blind have some remaining vision. |
| Causes | Cataracts, glaucoma, diabetes, macular degeneration, optic neuritis, neuropathy, congenital cataracts, infantile glaucoma, retinopathy of prematurity, keratoconus, etc. |
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What You'll Learn
Visual acuity: 20/200 or worse, even with correction
Visual acuity is the clarity or sharpness of vision. It is a measure of visual performance and does not relate to the eyeglass prescription required to correct vision. Instead, an eye exam seeks to find the prescription that will provide the best corrected visual performance achievable.
Visual acuity is typically measured at a distance of 20 feet. If you have 20/20 vision, you can see clearly at 20 feet what should normally be seen at that distance. If you have 20/100 vision, you must be as close as 20 feet to see what a person with normal vision can see at 100 feet. The lowest number in measurements like 20/100, 20/200, and 20/400 is the best. So, 20/20 is considered perfect vision.
A person with 20/200 visual acuity or worse, even with the best correction, is considered to be legally blind. This means that even with glasses or contact lenses, a person with 20/200 vision or worse still has 20/200 eyesight or worse in the centre of their field of view. To put it another way, a person with 20/200 vision would need to be 20 feet from an object to see it as well as someone with 20/20 vision could see it from 200 feet away. This is the threshold for "legal blindness" in the US, but other countries use different terms or define even more severe levels of vision impairment. For example, the United Kingdom uses the metric system, and 6/60, which is about the same as 20/200, means "sight impaired (partially sighted)".
It is important to note that "legal blindness" is a specific status set by government agencies and is not a medical term but a guideline. It is defined by law establishments as a level of visual impairment that limits the activities performed by individuals without assistance. A person who is legally blind may still have some usable vision, unlike a completely blind person.
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Limited field of view: no more than 20 degrees
"Legally blind" is a specific status set by government agencies. It is not a medical term but a guideline. It is defined by law establishments as a level of visual impairment that limits the activities performed by individuals without assistance. The American Medical Association defines "legally blind" as having at least one of the following:
- 20/200 (or worse) eyesight, even with correction. This means that even with glasses or contacts, you still have 20/200 eyesight or worse in the center of your field of view.
- A field of view that’s no more than 20 degrees wide. This is also known as tunnel vision and can be caused by retinitis pigmentosa, glaucoma, stroke, and other disorders.
To put this into perspective, a person with a visual field of only 20 degrees can see things that are right in front of them without moving their eyes from side to side, but they cannot see anything on either side. This is because the field of view refers to the total area in which objects can be seen using side (peripheral) vision while the person focuses on a central point. A normal visual field for both eyes is 180 degrees. Binocular vision, which is important for depth perception, covers 114 degrees (horizontally) of the visual field in humans, and the remaining peripheral ~50 degrees on each side can be seen with only one eye.
It is important to note that a person who is legally blind has some usable vision, unlike a completely blind person. About 80% of individuals who are blind have some remaining vision. Many diseases that cause blindness affect a certain part of vision and then progress to take away more vision. For example, macular degeneration initially affects a person's central vision (the vision that lets us see straight ahead).
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Peripheral vision: trouble seeing objects from the side
Peripheral vision is what you can see above, below, and to each side of your face without moving your head. It is everything except your central vision, which is what you see directly in front of you. Peripheral vision is naturally a little less clear than central vision.
Tunnel vision is another term for peripheral vision loss. It makes it hard or impossible to see objects that aren't directly in front of you. It can be caused by conditions that affect the eyes or other parts of the body that help with sight, such as blood vessels. Some of the most common eye diseases that cause tunnel vision include retinitis pigmentosa, diabetes-related retinopathy, retinal detachment, optic neuritis, and retinal vein occlusion.
Glaucoma, a condition caused by increased pressure within the eyeball, can also lead to tunnel vision. It is one of the most common causes of vision loss and can result in severe vision loss to the point of legal blindness. Glaucoma is more likely to occur in African Americans, those over 60, or individuals with a family history of the condition. Regular exercise can help reduce eye pressure, thereby reducing the risk of glaucoma.
To determine peripheral vision loss, an eye care provider will conduct a visual field test. This test is painless and will determine how far up and down and to each side a patient can see without moving their head. The test also shows how sensitive the patient's vision is in every part of their visual field.
In summary, peripheral vision loss or tunnel vision can make it difficult to see objects from the side without turning one's head. It is often caused by underlying eye conditions or health issues and can be diagnosed through a visual field test.
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Low vision: difficulty performing ordinary tasks with sight
Low vision is a term used to describe a level of visual impairment that makes it difficult to perform ordinary tasks, even with the best glasses or contact lenses. It is important to note that low vision is not the same as complete blindness, as individuals with low vision typically have some usable vision remaining. This means they may be able to see light and perceive objects, but their ability to perform everyday tasks is significantly impacted.
People with low vision may experience a range of difficulties in their daily lives. For example, reading or other close-up tasks may become challenging, and they may need to hold books or phones at arm's length to see clearly. They may also experience symptoms such as headaches, sore eyes, or tired eyes due to the extra effort required to focus and perceive objects.
One specific example of low vision is macular degeneration, which affects a person's central vision. This type of vision allows us to see straight ahead, so individuals with macular degeneration may struggle with tasks that require them to look directly at an object. This can include activities such as reading, driving, or recognising faces.
Another example is glaucoma, which can cause a decrease in vision by increasing the pressure within the eyeball. Glaucoma typically presents no symptoms or pain until noticeable vision loss occurs. This can make it challenging for individuals to navigate their surroundings, recognise objects, or perform detailed tasks that require clear vision, such as sewing or working with small objects.
The impact of low vision on daily tasks can vary from person to person, and it is important to understand the specific challenges faced by each individual. While some people may lose a significant amount of vision in a short period, others may experience a gradual decline over time. Additionally, certain eye conditions may affect specific aspects of vision, such as central vision or peripheral vision, further influencing the types of tasks an individual may find challenging.
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Causes: cataracts, glaucoma, congenital conditions, etc
Legal blindness is distinct from total blindness, as a legally blind person can still see, but not clearly. While a completely blind person cannot see anything, including light, a person with legal blindness retains some usable vision. This definition is used by government agencies to determine eligibility for benefits, such as disability or job training.
Cataracts, the clouding of the eye's natural lens, are the most common cause of vision loss leading to legal blindness. They can be the result of genetic disorders, diabetes, or trauma to the eye. Glaucoma, a condition of increased pressure within the eyeball, can also cause legal blindness by damaging the optic nerve and decreasing vision. This condition is often asymptomatic until noticeable vision loss occurs.
Congenital conditions, present at birth, can also lead to legal blindness. These include congenital cataracts, infantile glaucoma, and retinopathy of prematurity. Keratoconus, a gradual thinning of the cornea, can also cause severe vision loss.
Other causes of blindness include injuries, infections, and medical conditions. Eye injuries can occur in various ways, including chemical burns, industrial accidents, and motor vehicle crashes. Many infectious diseases can lead to vision loss, such as trachoma, cytomegalovirus, endophthalmitis, and histoplasmosis. Additionally, nutritional deficiencies, specifically vitamin A deficiency, can result in nutritional blindness, causing difficulty seeing at night or in dim light.
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Frequently asked questions
Legal blindness is a classification issued by the US government to establish eligibility for certain benefits and services. It is defined as having central vision in the better eye of 20/200 or less with corrective lenses, or a visual field of 20 degrees or less.
A person who is legally blind has some usable vision, unlike a completely blind person. Complete blindness implies the inability to see anything, including light, whereas partial blindness indicates limited vision.
To be legally blind, you must meet one of two criteria: reduced central visual acuity of 20/200 or worse in the eye with the best vision, or a limitation of your field of view to no more than 20 degrees.
Legal blindness can be diagnosed through a Snellen eye chart test and a confrontational visual field test. A doctor of optometry would issue a Certificate of Legal Blindness.
Certification of legal blindness enables access to federal, state, and local benefits and services, including financial aid for assistive technologies, guide dogs, tax deductions, educational scholarships, vocational training, and housing and transport assistance.
