Legal blindness is a specific classification of vision loss, distinct from total blindness or simply having poor eyesight. This definition serves as a legal and medical designation, primarily used to determine eligibility for various services, benefits, and accommodations. It is a standardized measure that allows for consistent application across different agencies and programs.
Defining Legal Blindness
The primary criterion for legal blindness in the United States is based on visual acuity. An individual is considered legally blind if their best-corrected visual acuity is 20/200 or less in their better-seeing eye. This means that a person with legal blindness must be as close as 20 feet to discern an object that a person with normal 20/20 vision can clearly see from 200 feet away.
This definition is largely established by federal law, specifically outlined within the Social Security Act. The measurement is typically conducted using a Snellen eye chart, which presents letters of decreasing size.
Best Corrected Vision
The determination of legal blindness always relies on “best corrected vision.” This means that visual acuity is measured after a person has utilized all available corrective measures. Such measures can include eyeglasses, contact lenses, or even vision correction achieved through surgical procedures.
If a person’s vision can be improved to better than 20/200 with these aids, they are not classified as legally blind based on visual acuity alone. It considers the maximum visual capability achievable with the most effective optical correction.
The Role of Visual Field
Beyond visual acuity, legal blindness can also be defined by a significant restriction in a person’s visual field. This refers to the entire area an individual can see without moving their eyes. A person is considered legally blind if their visual field is no greater than 20 degrees in its widest diameter in the better eye.
This condition is often described as “tunnel vision” because it severely limits peripheral sight. Individuals with such a restricted visual field may have clear central vision but struggle to perceive objects outside a narrow, direct line of sight.
Differentiating Legal from Total Blindness
It is a common misunderstanding that legal blindness implies a complete absence of sight. In reality, most individuals who are legally blind still possess some residual vision. They may be able to perceive light, shapes, colors, or even large print.
Total blindness, in contrast, refers to a complete lack of light perception. This means there is no ability to differentiate between light and darkness.