What is 20/20 Vision?

You’re probably familiar with the term 20/20 vision, but most people are unfamiliar with what it actually means. The term 20/20 refers to a specific line on the letter chart in your optometrist’s office and is a measure of the acuity or sharpness of your vision. 20/20 vision is often considered “perfect” vision, though many people are able to achieve better than 20/20 vision - often with the aid of correction. 

But what exactly do the numbers mean? The first twenty is the distance in feet the observer is from the chart. It should be noted that most exam rooms are less than 20 feet in length, and the letter charts are calibrated to account for this. The second twenty is the amount of detail a so-called average person can see at 20 feet. Details are the arms or lines on letters and the space between these arms. If a person sees better than 20/20 they might have 20/15 vision for example, meaning they can see at 20 feet what the average person can see at 15 feet. An example of vision worse than 20/20 would be 20/40 vision. This means a person sees at 20 feet what the average person sees at 40 ft, so they have to be closer to something to be able to see it clearly. 

Patients will often declare they’re legally blind, then rattle off the 20/20 line through their glasses. This is a common misconception. Legal blindness is usually considered 20/200 vision, with correction (among other factors). This means that even with their glasses a legally blind person can see at 20 feet what an average person can see at 200 feet. If your vision is correctable beyond 20/200 you are likely not considered blind, though things might be a little blurry without your glasses. 

There is also some misconception about the visual acuity requirements for driving. In Ontario drivers must be able to see the 20/50 line with or without correction. This means that in order to be able to drive you must be able to see at 20 feet what the average person can see at 50 feet. If a driver must wear glasses to achieve this it will be noted on their license. If at your eye exam it is discovered that glasses are now required to drive, your optometrist will let you know of the finding and alert the ministry to update your license. If it is found that the requirement cannot be met, even with glasses, the same will be done and the ministry will have to revoke the license. 

20/20 is not the only way to measure vision but it is by far the most common. There are other measures of vision, such as colour vision, contrast sensitivity, and peripheral vision. These other measures of vision are sometimes required for certain occupations. Your optometrist is able to test these other vision tests, should you require them.