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What does "legally blind" mean?

Silhouette of blind man with his guide dog
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“Legally blind” means you’re essentially sightless in the eyes of the law if eyeglasses or contact lenses cannot correct your vision beyond specific standards.

How do we define who’s legally blind?

In the U.S., the standard definition of legal blindness is based on central visual acuity (what’s in front of you) and field of vision (what’s above, below and to the sides).

By this definition, you’re legally blind if your better eye — when using a corrective lens — has a central visual acuity of 20/200 or lower, or field of vision of no more than 20 degrees.

It’s good to know the definition of legal blindness because it can affect your ability to get a driver’s license or receive government disability benefits.

Measuring your visual acuity

When your eye doctor asks you to read the smallest row of letters from across the room, you’re looking at the Snellen chart, the U.S. standard for measuring clarity of eyesight.

The eye chart assumes a base viewing distance of 20 feet and compares your vision to the historical norm for most humans.

If you have 20/20 vision, then the smallest letters you can read from 20 feet away match the normal 20-foot distance. By contrast, 20/200 vision means the letters you can read from 20 feet can be read from 200 feet by people with normal vision. Thus, you see only one-tenth of the norm.

Measuring your visual field

Some people can see small letters on an eye chart but can't see the person standing next to them. That’s because they have legal blindness due to poor peripheral vision. A wide visual field is crucial for activities like driving a car or crossing a busy street.

Visual field tests determine if you have a normal field of view that has no blind spots or unusual narrowing of your peripheral vision.

Peripheral vision has two parameters: lateral (side to side) and vertical (up and down). A maximum lateral field of view is nearly 180 degrees; distant objects remain visible from the right or left of the observer.

The normal vertical field is smaller at about 135 degrees.

You are considered legally blind if testing finds your peripheral vision is 20 degrees or less (a condition often called tunnel vision).

How many people are legally blind?

About 1 million Americans were legally blind  in 2015, according to the most recent estimate from the recent estimate from the National Eye Institute.

The same report noted that 3.2 million Americans had low vision (20/40 or worse with best correction), while 8.2 million had uncorrected vision problems.

As the nation’s population ages, the number of legally blind Americans is expected to double by the year 2050. 

Causes of legal blindness

Though some people become blinded in accidents, a host of conditions can cause a visual disability or legal blindness.

Four leading causes of legal blindness  in the United States are age-related macular degeneration (AMD or ARMD), cataracts, diabetic retinopathy and glaucoma.

Optic neuritis and neuropathy also can cause legal blindness, as can a number of congenital conditions such as congenital cataracts, infantile glaucoma and retinopathy of prematurity.

Keratoconus, a gradual thinning of the cornea, also can cause severe vision loss to the point of legal blindness. (See "Is keratoconus a disability?")

Resources for those who are legally blind

Legal blindness can make people eligible for special services and assistance.

The Social Security Administration provides benefits to the legally blind. States and federal taxing authorities also allow tax deductions. Multiple non-governmental resources help make it easier to lead a normal life even with severe vision impairment.

If you are legally blind or you are a guardian or care provider for someone who is, seek the services of an eye doctor who specializes in low vision.

Low-vision specialists typically are familiar with the latest vision aids such as magnifiers, telescopes and digital devices that can help you make the best use of any vision you still have.

These devices often help a person with legal blindness live more independently and enjoy activities that everyone else takes for granted.

Professionally trained guide dogs also are a great help for many people who are legally blind.


Legally blind? Don't let it stop you from voting

U.S. law decrees that all Americans — disabled or not — must have the same opportunity to vote.

Elderly man voting with the help of a woman in red

At every polling place, voting machines should be functional, and poll workers should be able to help people use them.

That means we all have the right to vote independently and privately. We are all entitled to an accessible polling place with voting machines for people with disabilities including blindness.

Over the years, people with visual disabilities have reported that polling places have had:

  • Voting machines that were either unavailable or broken.
  • Machines without magnifying glasses and/or audio headsets.
  • Poll workers who didn't know how to use the machines and couldn't help disabled voters.

In some cases, disabled voters had to give up their privacy rights and have someone fill out a paper ballot for them.

If you are visually disabled, don't let these problems keep you from voting. Before an election, contact local election officials  and ask about the polling place to make sure it is accessible and has functioning machines if you need one.

If you’re unsure of your rights, read more about the Americans with Disabilities Act .

Often, election officials will know of organizations that can transport you to and from the polls. And they can advise you of the availability of mail-in absentee ballots and how far in advance you need to request one.

After the election: If you feel your voting experience was not fair, independent and private, then speak up. Tell the poll workers and election officials about your experience. They need to know what happened so they can prevent problems in the future.

You can also file a complaint  with the Voting Section of the U.S. Department of Justice.

Page updated November 2019

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