Visual acuity is a common measure of vision that often leads to confusion regarding the severity of eye impairment. The clarity and sharpness of sight are assessed using a standardized measurement system. Many people who experience diminished vision wonder if their measurement meets the specific federal standard for blindness. This article clarifies the difference between a common visual impairment score and the precise criteria established for legal blindness.
Understanding the Snellen Scale and Visual Acuity
Visual acuity is formally measured using the Snellen chart, a tool that determines the sharpness of your distance vision. This test assigns a fractional score, such as 20/20, 20/80, or 20/200, to represent the clarity of sight. The first number, 20, indicates that the person is standing 20 feet away from the eye chart during the test.
The second number represents the distance at which a person with normal, or 20/20, vision can clearly read the same line of letters. This measurement serves as the baseline for what is considered average, well-corrected vision.
A visual acuity of 20/80 means that you must stand at 20 feet to see what a person with 20/20 vision can see from 80 feet away. In practical terms, your sight is one-fourth as good as the average person’s. This level of impairment can make tasks like reading road signs or recognizing faces at a distance noticeably challenging.
The Official Threshold for Legal Blindness
The term “legal blindness” is not a medical diagnosis of total sight loss but rather a classification established by the government to determine eligibility for specific services and benefits. In the United States, this definition is utilized by agencies like the Social Security Administration (SSA) to qualify individuals for disability assistance. The standard is precise and is defined in the Social Security Act as part of the federal definition of disability.
The primary criterion for legal blindness is a central visual acuity of 20/200 or worse in the better eye, even after the best possible correction with glasses or contact lenses. A person with 20/200 vision can only see at 20 feet what an average person can see from 200 feet away.
Does 20/80 Meet the Legal Standard?
A visual acuity of 20/80 does not meet the legal standard for blindness in the United States. This measurement is significantly better than the 20/200 threshold required for the legal classification. While 20/80 is a substantial visual impairment that can affect daily activities, it falls into the category of “low vision” or “moderate visual impairment”.
The gap between 20/80 and 20/200 is considerable, as 20/80 vision is two and a half times better than 20/200 vision. A person with 20/80 sight still retains a greater degree of functional vision compared to someone who is legally blind solely based on acuity. Although a 20/80 score can qualify an individual for certain low-vision aids and services, the impairment does not cross the specific line set for federal disability benefits related to legal blindness.
Visual Field Restrictions and Other Factors
Visual acuity is only one part of the official legal blindness definition; the other component involves the visual field, which is the entire area a person can see without moving their eyes. A person can also be classified as legally blind if their visual field is severely restricted. This is measured by determining the extent of a person’s peripheral, or side, vision.
The specific visual field restriction required for legal blindness is a field of 20 degrees or less in the better eye. This condition is often described as having “tunnel vision” because the person’s view is severely narrowed. This criterion is separate from the 20/200 acuity standard. Therefore, a person with 20/80 visual acuity could still be classified as legally blind if their peripheral vision meets the severe 20-degree restriction.