The term “legally blind” is not a medical diagnosis but a specific designation established primarily for administrative and governmental purposes. This standardized definition allows various agencies to determine eligibility for support programs and accommodations based on measurable metrics of vision loss. It serves as a bureaucratic threshold to ensure consistent access to services for people whose visual impairment significantly impacts their daily lives.
The Numerical Definition of Legal Blindness
The United States government defines legal blindness using two numerical criteria related to the best-corrected vision in the better eye. The most commonly cited criterion involves visual acuity, which must be 20/200 or less with the use of corrective lenses, such as glasses or contact lenses. This measurement is typically performed using a Snellen chart, where 20/20 is considered normal vision.
The fraction 20/200 means a person must stand 20 feet away to clearly see an object that a person with normal vision can see from 200 feet away. Essentially, the visually impaired person needs to be ten times closer to an object to achieve the same clarity as someone with 20/20 vision. This level of impairment is the threshold for legal blindness in terms of central vision sharpness.
The second way to meet the legal blindness definition involves a restriction of the visual field, even if central visual acuity is better than 20/200. This peripheral vision restriction, often referred to as “tunnel vision,” must be 20 degrees or less in the widest diameter. A normal visual field is approximately 180 degrees, so this criterion represents a severe loss of side vision.
Legal Blindness Versus Total Blindness
Many people mistakenly believe that being legally blind means having no vision whatsoever, but this is generally not the case. The legal designation covers a broad spectrum of visual disability, and most people who are legally blind still have residual vision. This vision can range from the ability to perceive light and distinguish between light and dark, to having limited object recognition.
Total blindness, in contrast, is defined as the complete lack of both form and light perception. This is clinically recorded as “no light perception” and represents the most severe form of vision loss. Only a small percentage of people who meet the criteria for legal blindness are considered totally blind.
The majority of individuals labeled legally blind have what is commonly referred to as low vision, meaning they retain some functional sight. This functional vision can often be used for tasks like mobility or reading with the aid of specialized devices.
Accessing Support and Services
Meeting the numerical threshold for legal blindness serves as the gateway to various forms of support and accommodations. The official designation qualifies individuals for government aid programs designed to mitigate the challenges of severe vision loss. These programs include Supplemental Security Income (SSI) and Social Security Disability Insurance (SSDI), which provide financial assistance.
The designation also unlocks access to vocational rehabilitation services, helping people acquire skills for employment and adjust to life with impaired vision. Legally blind individuals may also be eligible for specialized educational resources, tax benefits, and certain transit or travel concessions. For safety reasons, the legal blindness designation generally prohibits obtaining or maintaining a standard driver’s license.
Special rules, such as work incentives within Social Security programs, allow legally blind individuals to continue receiving benefits even if they are employed, provided their earnings remain below a specific limit. This framework recognizes the difficulty of securing and maintaining employment when facing severe visual impairment.