Legal blindness is a classification that often causes confusion, especially regarding whether vision is assessed with or without corrective lenses. This definition is a legal designation, not a medical diagnosis, used to determine eligibility for various services and benefits. Understanding these criteria clarifies common misconceptions about the term.
Understanding Legal Blindness
Legal blindness refers to a specific level of central visual acuity, which is the sharpness of vision when looking straight ahead. In the United States, this criterion is defined as 20/200 or less in the better eye, even with the best possible corrective lenses like glasses or contact lenses. This means a person must stand at 20 feet to see what someone with normal vision (20/20) sees clearly from 200 feet away.
Visual acuity is determined using a Snellen eye chart. An individual reads the smallest line of letters they can discern from a standard distance, usually 20 feet. If, with best correction, they can only read the top, largest letter (20/200 line), or nothing smaller, they meet this part of the definition.
The Importance of Visual Field
Beyond central visual acuity, legal blindness can also be determined by a significant restriction in a person’s visual field. The visual field encompasses the entire area one can see without moving their eyes. A person is considered legally blind if their visual field is 20 degrees or less in the better eye.
This condition is often called “tunnel vision” because it limits peripheral sight, making it seem as though one is looking through a narrow tube. Even if central vision is better than 20/200, a severely constricted visual field can still qualify an individual for legal blindness. This limitation significantly affects daily activities, such as navigating crowded spaces or driving.
Why Uncorrected Vision Is Not the Standard
A common misunderstanding is that legal blindness is determined by vision without correction. However, the official definition explicitly states that visual acuity must be measured with best correction. Many individuals have significantly impaired vision without their glasses or contact lenses, potentially seeing worse than 20/200. Despite this, if their vision can be improved to better than 20/200 with corrective eyewear, they are not considered legally blind by the established criteria.
For example, someone with a very high prescription might struggle to see clearly without corrective lenses. They might informally say they are “blind without their glasses,” but this functional experience differs from the legal classification. The legal definition identifies individuals whose vision loss is so severe it cannot be adequately improved by conventional means, impacting their ability to perform daily tasks. Therefore, prescription strength alone does not dictate legal blindness; the uncorrectable nature of the impairment is key.
What Legal Blindness Means
Legal blindness is a governmental classification, not a medical diagnosis of total sight loss. Most individuals who are legally blind retain some usable vision, ranging from light perception to distinguishing shapes and colors. Only a small percentage of legally blind people experience total blindness, meaning no light perception.
This classification serves an important purpose: it determines eligibility for various government programs and support services. These benefits can include Social Security Disability payments, tax exemptions, vocational training, and specialized educational resources. Eye care professionals diagnose legal blindness through comprehensive eye examinations, including visual acuity tests like the Snellen chart and visual field tests. This designation helps ensure individuals with severe, uncorrectable vision impairments receive the necessary assistance to navigate daily life and access needed support.