Vision measurement uses numerical expressions to describe how clearly someone can see. These figures, often encountered when discussing eye health, can be confusing. This article explains common methods for assessing vision and clarifies less common terms.
How Visual Acuity is Measured
Visual acuity is typically measured using a Snellen chart. This chart features rows of block letters that decrease in size from top to bottom. During an eye examination, a person stands a specific distance from the chart, commonly 20 feet (or 6 meters), and reads the smallest line of letters they can discern.
Results are expressed as a fraction, such as 20/20. The first number indicates the testing distance, usually 20 feet. The second number represents the distance at which a person with “normal” vision can clearly read the same line. For example, 20/20 vision means a person can see at 20 feet what someone with normal vision also sees at 20 feet.
Vision better than 20/20 is indicated by a smaller second number, such as 20/15 or 20/10. This means a person can see at 20 feet what someone with normal vision would need to be 15 or 10 feet away to see. Conversely, a larger second number, like 20/40, means a person must be as close as 20 feet to see what someone with normal vision can see from 40 feet away.
Understanding 19/19 Vision
The term “19/19 vision” is not a standard measurement used by eye care professionals. Visual acuity measurements are conventionally based on a 20-foot (or 6-meter) testing distance, which is why fractions like 20/20 are widely recognized. The Snellen chart and its notation are designed around these established distances.
If the principle of the Snellen chart were applied directly to “19/19 vision,” it would imply that a person could see at 19 feet what someone with normal vision could also see at 19 feet. In this hypothetical scenario, it would suggest a clarity of vision equivalent to what is considered “normal” at that specific distance. However, this measurement is not used in clinical practice.
The consistent use of 20/20 (or 6/6 in metric systems) provides a universal benchmark for normal visual acuity. While mathematically “19/19” might seem to convey similar clarity, it deviates from the standardized testing distances and reporting conventions of eye care professionals. This non-standard terminology means it is not used to describe visual capabilities in a professional context.