This is the year for optometrists and eye nerds around the world – 2020! So many people brag about his or her 20/20 vision, but what does that really mean?
What is 20/20?
“20/20 vision” is a unit of visual acuity (or clarity) measured at a specific distance. While 20/20 is considered normal vision for healthy eyes, many people can see letters even smaller. The 20/__ nomenclature is really a measurement of eyesight and not vision. The difference is not commonly acknowledged by the general public, but clinically speaking, there is a significant discrepancy. Eyesight refers to visual acuity measured in terms of 20/__. On the other hand, vision includes the ability to see colors, moving objects, peripheral vision, and depth perception.
Measuring Visual Acuity
The Snellen eye chart is most commonly used to measure visual acuity. Results are written using Snellen fractions (20/20, 20/30, 20/40, etc).
The top number of the fraction represents the testing distance (ie. the standard 20 feet). Most exam rooms use mirrors to achieve the 20 feet distance, as it is difficult to have exam rooms 20 feet long. Other countries measure vision in terms of meters, which makes 20/20 equivalent to 6/6.
The letters on the eye chart are calibrated to different sizes, which represent different levels of eyesight. The larger the letters, the worse the eyesight and the higher the bottom number of the fraction. The “big E” is usually 20/200 or 20/400 based on the digital system. The smaller the letters, the better the eyesight, and the lower the bottom number of the fraction. 20/15 and 20/10 are even more exceptional than the normal 20/20.
The letters are displayed with high contrast conditions – black letters on a white background. Acuity is always measured one eye at a time because it helps determine if one eye is seeing differently than the other. It is possible to have a nearly blind eye and not realize it until the good eye is covered. The dominant eye can carry the team without even noticing.
Interpreting Visual Acuity
Here is an example of how to interpret a visual acuity other than 20/20:
20/100 means a person needs to stand 20 feet away from an object to see it, whereas a person with normal vision could see the same object from 100 feet away.
People who are unable to read 20/20 might benefit from the use of glasses or contact lenses. Hyperopia (farsightedness) or presbyopia (natural slowing of the focusing system) is when a person can see well in the distance, but has trouble reading up close. Myopia (nearsightedness) is the opposite – a person can read well at near, but struggles to see clearly in the distance.
Perfect Vision is More Than 20/20
There is much more to vision than reading the 20/20 line on the eye chart. Other vision skills include eye teaming (how well the eyes work together), color vision, peripheral vision, depth perception, and focusing ability. If one of these skills is impaired, it can affect the entire ocular system and cause symptoms (headache, eyestrain, double vision, etc).
Having 20/20 vision does not mean that an eye exam is unnecessary…quite the opposite! We want to preserve the excellent vision by making sure the health of the eyes, both inside and out, is normal. A comprehensive eye exam goes much further beyond just reading the eye chart. Call our office to schedule your annual eye exam.
All of us at Weber Vision Care hope you have a SPECtacular 2020.
