Visual acuity describes the clarity or sharpness of a person’s vision, measuring how well the eye can distinguish fine details and shapes. This measurement is a standard component of any comprehensive eye examination and is recorded as a fraction to assess how clearly a person sees at a specific distance. Understanding this fraction is the first step toward interpreting the severity of a vision measurement like 20/200.
Understanding the Snellen Scale
Visual acuity is most commonly measured using the Snellen chart, which presents rows of letters that decrease in size. The result is expressed as a fraction, such as 20/20 or 20/200, providing a standardized comparison to normal vision. The numerator (top number) represents the standard distance the patient stands from the chart, typically 20 feet.
The denominator (bottom number) indicates the distance at which a person with normal vision could read the same line the patient read at 20 feet. For example, 20/20 vision means the patient sees clearly at 20 feet what a person with normal vision sees at 20 feet. A larger denominator indicates poorer vision because the patient must be closer to the chart than average to read the same line.
What 20/200 Vision Specifically Means
Applying the Snellen principle, 20/200 visual acuity signifies a substantial degree of vision impairment. It means a person must stand 20 feet away from an object to see it with the same clarity that a person with normal vision (20/20) can achieve from 200 feet away. This means the individual with 20/200 vision needs to be ten times closer to an object to distinguish the same details.
This level of impairment significantly affects the ability to perceive details at a distance. Someone with 20/200 vision would find it difficult to read street signs, recognize faces across a room, or safely operate a motor vehicle. Objects far away appear heavily blurred and indistinguishable, making many routine tasks challenging without specialized assistance.
20/200 and the Designation of Legal Blindness
The measurement of 20/200 vision is the threshold used in the United States to define one part of the criteria for “legal blindness.” An individual is considered legally blind if their visual acuity is 20/200 or worse in their better-seeing eye, even after the best possible correction with glasses or contact lenses. This designation means their sight is severely limited, not that they cannot see anything.
The official definition also includes a secondary criterion related to the field of vision. If a person’s visual field (the total area they can see without moving their eyes) is restricted to 20 degrees or less, they also meet the definition of legal blindness, regardless of their central acuity. This legal status is established by government agencies to determine eligibility for various benefits, including disability services and tax exemption programs.