Everyone has heard of 20/20 before. Maybe you heard someone boasting about their excellent eyes. Perhaps you heard an optician or a laser eye surgery provider talking about how great Lasik can be. We’ve all heard about it. But do we know what it really means? Or how it came about? What does 20/20 vision mean in terms of our day to day eyesight?
The “20” refers to 20 feet. This is the distance from which your optician checks your visual acuity. Visual acuity means sharpness of vision. It is measured by the ability to discern letters or numbers at a given distance according to a fixed standard. In countries that use the metric system, you might hear 6/6 vision. This refers to 6 meters which approximately equals 20 feet.
Visual acuity depends on the following physical factors:
- The ability of your brain to interpret information transmitted from your eyes.
- How sensitive the nerves in your retina are, as well as the vision centers in the brain.
- The ability of the cornea and lens of the eye to focus light onto the retina accurately.
Measuring visual acuity
All opticians will always take these measurements from the same distance. They make sure their patients are sitting still. The chart will be in high contrast (e.g. black on white). The downside is that your official, recorded visual acuity only indicates one aspect of your vision. It only tests how well you can see a highly contrasted test from a distance. It does not indicate how well you can see color or moving objects. It also does not measure your eye’s:
- Close-up vision or “near vision”
- Depth perception
- Peripheral vision (seeing to the sides)
- The ability to see colors
However, this test does not indicate how sharp your vision is. This is essential for prescribing you glasses. It is also important to know this if you want to get laser eye surgery. Your laser eye surgeon will need to know the details of your vision in order to treat you correctly.
It’s important to get your eyes checked regularly. Beyond checking just your vision, eye tests can detect serious problems like glaucoma, macular degeneration, and sometimes even brain tumors. Your sight is probably one of the most important senses you have. It’s vital to take every possible step to protect it.
Is 20/20 vision really normal?
Some people see better than 20/20, perhaps around 20/15, some see a bit less at 20/25. 20/20 is simply just an average. When Snellen invented the test, it is possible that the sharpness and contrast of the text he used was different from what we currently use as a standard.
The resolution of our central vision is somewhat like a high-resolution computer monitor. If the pixels are close together and fine, the overall resolution is better. TV manufacturers study visual acuity. At a certain point, the resolution of a TV can be higher than even the best human vision can detect.
What is the Snellen chart?
Even if you don’t know the name of it, you’ve probably seen a Snellen chart before.
The Snellen test is a chart of letters or symbols. You’ve probably seen it at the eye doctor’s office or in the school nurse’s office. The letters are different sizes. They are arranged in rows and columns. The Snellen chart was developed in 1862. It was invented by a Dutch ophthalmologist named Herman Snellen. It is now used across the world to measure people’s visual acuity.
During the test, you will stand at a distance from the chart. Your optician will have you cover one of your eyes. Next, you will read the letters out loud from your uncovered eye. You will continue to read smaller and smaller letters. You keep going until you can no longer distinguish the letters accurately.
The first letter on the chart is an “E.” If this is the only thing you can see, you have 20/200 vision. This means you are legally blind. You can see what a person with normal vision can read from 200 feet away.
Each line on the chart corresponds to better vision as you go further down. The fifth line indicates 20/40 vision. This is what you need to have in order to drive without vision correction.
Is it possible to have 20/20 in one eye but not the other?
Yes. It’s entirely possible for your vision to be perfect in one eye but not the other. When opticians or doctors check your visual acuity, they test one eye at a time. Next, they test the eyes together. Many people have one eye that is stronger than the other and will need less of a vision correction in that eye.
Can you have better than 20/20?
It’s possible, but rare.
If you can read the bottom line on the chart, you have 20/10 vision. So it’s quite possible for people to have better vision than 20/20. It’s just very uncommon. Less than 1% of the general population has 20/10 vision. However, most young people with healthy eyes can read some of the letters on the 20/15 line. What this means is that someone with 20/10 vision has visual acuity that is twice as good as the average person. Someone with 20/40 has visual acuity twice as worse as the average person.
The world record for best visual acuity in a human is 20/8. The best vision that scientists know of are in eagles. Eagles have somewhere between 20/5 and 20/4 vision.
What does it mean to be legally blind?
Formally, legal blindness means a central visual acuity 20/200. This is in your better eye with the best possible correction. What this usually means is that you can’t see much more than the letters on a stop sign.
Contact the Shreveport Eye Specialists
What does 20/20 vision mean? Find out by speaking to a Shreveport Eye Specialist. If you are curious about your visual acuity or are due for an eye exam, contact the experts at Shreveport Eye Specialists today at 318-771-7597. Take care of your most important sense and schedule a consultation and exam. You can also leave a message for the team on our contact page.