“20/20” is probably the most famous number in eye care. Patients often ask me whether it means perfect vision. It does not, and understanding why helps you get more out of every eye exam.
What the numbers mean
The test is done from 20 feet away. The first number is your distance from the chart. The second number is the distance at which a person with typical vision could read the same line. So 20/20 means you can read at 20 feet what a typical person reads at 20 feet. With 20/40 vision, you need to be at 20 feet to read what a typical person can read from 40 feet away. Some people see better than 20/20, such as 20/15.
Why so many people are not 20/20 without help
According to the National Eye Institute, refractive errors are the most common type of vision problem, and more than 150 million Americans have one. They happen when the shape of the eye keeps light from focusing correctly on the retina. There are four common types:
- Nearsightedness (myopia): distant objects look blurry.
- Farsightedness (hyperopia): nearby objects look blurry.
- Astigmatism: things near and far can look blurry or distorted.
- Presbyopia: trouble seeing up close, common from about age 45.
The NEI notes that many people with a refractive error do not know they could be seeing better, which is one reason regular exams matter.
What 20/20 does not measure
The eye chart tests sharpness at a distance, in good lighting, with high contrast. It does not test:
- Side (peripheral) vision, which glaucoma can damage silently
- Depth perception and how the two eyes work together
- Color vision and contrast in dim light or fog
- The health of the retina, optic nerve and lens
You can read the 20/20 line and still have early glaucoma, diabetic changes in the retina, or a cataract starting to form. That is why a full exam includes eye pressure, a look at the back of the eye, and often dilating drops, not just the chart.
A practical takeaway
If your vision seems fine, keep your regular exams anyway. If your vision has changed, even on one side, do not wait for your next routine visit. To schedule, call our Westlake Village office at (805) 230-2126.
When patients ask me for 20/20, I tell them that clear sight is the goal, but healthy eyes are the foundation.
Source: Refractive Errors (National Eye Institute (NIH)). This article is an educational summary written by Khanna Vision Institute and is not a substitute for medical advice.