The term “legally blind” is an administrative designation defining a specific level of severe vision loss, often confused with total blindness. This status is not a medical diagnosis; instead, it is a standardized threshold used by government agencies to determine eligibility for various resources, support programs, and financial assistance. This designation ensures that individuals with profound visual impairment can access necessary services, acknowledging that most people classified as legally blind still retain some functional vision.
Defining the Legal Threshold
Legal blindness is determined by two distinct, measurable criteria involving the best-corrected vision in the better-seeing eye. The first criterion relates to central visual acuity, which must be 20/200 or less, even with corrective lenses. The second criterion focuses on the width of the visual field. A person can still be classified as legally blind if their peripheral vision is severely restricted, requiring the field of vision to subtend an angle of no greater than 20 degrees.
Understanding Visual Acuity Measurement
Visual acuity measures the clarity or sharpness of vision and is typically assessed using a Snellen eye chart. The fraction 20/200 represents a ratio comparing the distance at which a person is tested to the distance a person with normal 20/20 vision could read the same line. Specifically, a person with 20/200 vision must stand 20 feet away to read letters that a person with standard vision reads from 200 feet. The specific phrase “with best correction” is a component of the legal definition, meaning the measurement must be taken while the person is wearing the most effective corrective lenses or optical aids. Therefore, the prescription itself is not the defining factor; rather, it is the vision outcome after correction that determines legal blindness status.
The Criterion of Peripheral Vision
The second path to legal blindness involves a significant limitation of the visual field, which is the entire area one can see without moving the eyes. This measurement is distinct from central acuity and is often evaluated using specialized equipment like a perimeter. The standard for legal blindness is met if the widest diameter of the visual field is restricted to 20 degrees or less. Since a normal visual field is approximately 160 to 170 degrees horizontally, this criterion represents a severe loss of peripheral vision, often described as “tunnel vision,” which can drastically impair mobility and navigation.
Implications of Legal Blindness Status
Meeting the definition of legal blindness opens the door to governmental benefits and specialized services intended to mitigate the challenges of severe visual impairment. This status is the gateway to financial support programs, including Social Security Disability Insurance (SSDI) and Supplemental Security Income (SSI), and allows individuals to qualify for specific tax exemptions. Furthermore, the status grants access to specialized educational and vocational rehabilitation programs. These services teach alternative techniques for daily living and employment, often including training in orientation and mobility, Braille literacy, and the use of adaptive technology. Finally, a classification of legal blindness results in an automatic inability to obtain or renew a driver’s license in all fifty states.