Legal blindness is a specific classification to describe a significant degree of vision loss. It does not mean a complete inability to see, but rather a level of vision impairment that meets defined criteria. This classification helps determine eligibility for various support services and benefits, distinguishing it from total blindness, which involves no light perception. Understanding this distinction involves examining how vision is measured and the thresholds established for legal blindness.
Understanding Key Vision Measurements
Visual acuity measures vision, indicating the clarity or sharpness of sight at a distance. It is assessed using a Snellen eye chart, which features rows of letters that decrease in size. The familiar “20/20” vision means a person can clearly see at 20 feet what someone with normal vision sees at 20 feet. In this notation, the first number is the distance from the chart, while the second indicates the distance a person with normal vision could read the same line.
The visual field, another important measurement, refers to the entire area a person can see without moving their eyes or head. This encompasses both central vision and peripheral, or side, vision. A normal visual field typically spans approximately 160-180 degrees horizontally and about 120 degrees vertically. Visual field tests measure this range in degrees, helping to identify any narrowing or blind spots in a person’s peripheral awareness.
The Official Definition of Legal Blindness
The official definition of legal blindness in the United States is based on specific visual acuity and visual field measurements. A person is considered legally blind if their central visual acuity is 20/200 or less in their better eye, even with the best possible conventional correction, such as glasses or contact lenses. This means that to see an object clearly, a legally blind individual must be as close as 20 feet to discern what a person with normal vision could see from 200 feet away.
Additionally, legal blindness can be defined by a severely restricted visual field. If an individual has a visual field no greater than 20 degrees in their better eye, they also meet the criteria for legal blindness. This condition is sometimes referred to as “tunnel vision,” where peripheral sight is significantly limited, even if central acuity is better than 20/200. It is important to note that meeting either the visual acuity criterion or the visual field criterion is sufficient for a legal blindness classification.
Life with Reduced Vision
Individuals classified as legally blind often experience significant challenges in performing daily activities. Tasks such as reading standard print can be difficult, often requiring magnifiers or specialized reading devices. Recognizing faces from a distance or navigating unfamiliar environments can also pose considerable obstacles. Due to their visual limitations, most legally blind individuals are unable to drive.
Despite these challenges, many legally blind individuals retain some usable vision. They may be able to perceive light, distinguish between light and dark, or see large shapes and movements. This residual vision allows for a degree of independence in their daily lives, often aided by adaptive techniques and technologies. The impact of legal blindness varies from person to person, depending on the specific nature and extent of their vision loss.
Distinction from Complete Blindness
Legal blindness is distinct from complete, or total, blindness. Total blindness signifies a complete lack of light perception, meaning an individual cannot see anything at all, not even light.
In contrast, the vast majority of individuals who are legally blind still possess some level of vision. While their vision is severely limited, it is not an absence of sight, allowing for varying degrees of visual interaction with their environment.