Simply put 20/20 vision is how many letters you can see on an eye chart from twenty feet away. Contrary to popular belief this is not perfect vision, it is “normal” or “average” vision. So, what is meant by “normal vision?”A person with 20/20 vision is able to see on an eye chart what the average person was able to see from 20 feet away.
Snellen Eye Chart & Vision Rating
The eye chart typically used to test for visual acuity (basically how much someone can see) is called the Snellen Eye Chart and it was first used for vision testing in 1862. It’s a series of lines of letters (typically the letters C, D, E, F, L, O, P, T and Z are used) that get increasingly smaller as they descend down the chart.
When rating a person’s vision, the top number is always 20. That number shows the distance at which the patient can clearly see a specific image (for vision testing patients are standing 20 feet from the eye chart). The second number specifies at what range the average person can see that same image (it also represents the size of the corresponding letters on the Snellen Eye Chart).
Each row of letters on the Snellen Eye Chart matches a specific Visual Acuity value. Below is an explanation ofsome eyesight values:
20/15: considered superior to 20/20. This means the person can see an object at 20 feet that a person with 20/20 vision was only able to see at 15 feet.
20/40: the minimum to be able to pass the Driver’s license test in all 50 states. Most printed materials (newspapers, etc.) are at this vision level.
20/80: patients at this level have greatly decreased vision but are still able to see sizes similar to the time on an alarm clock at a distance of 10 feet and read newspaper headlines at a normal distance.
20/200: Patients at this level are considered legally blind, and are only able to see sizes similar to the letters on a stop sign.
LASIK and vision testing
After undergoing LASIK surgery patients can often achieve vision greater than 20/20. Several studies have recently found that nearly 99% of all Lasik patients achieve at least 20/40 vision, and at least 90% attain 20/20 vision or better. The varying results are due to the type of LASIK surgery the patient undergoes and the original eyesight of the patient.