Everybody might have seen those number and letter charts once or twice in your life. Maybe when you were at the ophthalmologist fitting new glasses. Maybe when you were at the mall walking past a spectacles shop. Perhaps you have seen it on TV in a commercial, or somewhere else. But most people recognize this chart from somewhere.
The funny thing is almost nobody understands what this chart is or how it works. And this does not only apply to people who have good vision, but even people who wear glasses and visit ophthalmologists to do these tests often don’t know what the vision scoring chart is or how it works. Don’t feel ashamed if you don’t know. In this article we will explain what it is, how it works and also we go into depth into the different systems used in different countries.
The way we measure our eyesight varies from country to country. But one thing all countries have in common is that they are all derived from the Snellen chart, which was developed by Dr. Hermann Snellen in the 1860s. The Snellen letter chart features capital letters in rows of descending sizes. In Korea though, they use Korean letters, numbers and sometimes pictures and shapes for kids. Even though the methodology is the same, the way they sight is measured is different.
Most eye appointments in all these countries will determine how well you can see, whether that is direct vision, peripheral vision or color recognition. They’ll typically perform tests to check the overall health of your eye and look for factors which could impact your eyesight.
Typically, not all clinics are big enough to place the chart 20 feet or six meters away from the person being tested, so digital screens are now used that can be calibrated depending on how far away the person is sitting from the chart.
Below are the ways your vision is scored
United States of America
The Snellen test, or letter chart, is the most commonly used piece of equipment to test visual acuity and is also the test most people think of when they think of eye tests in the US.
In the US, they use “feet” as their measurement when measuring your vision. “Normal” vision is 20/20. This means that the test subject sees the same line of letters at 20 feet that person with normal vision sees at 20 feet. 20/40 vision means that the test subject sees at 20 feet what a person with normal vision sees at 40 feet. So your vision is getting worse if the second number increases. These figures are based on Snellen letter charts which are used in the standard eye test.
How does the UK assess visual acuity?
In the UK, 6/6 notation is used. The first number refers to the distance at which the chart is viewed (six meters) and the second number refers to the distance at which a person with ideal vision can see a letter clearly. So it’s a similar concept to the US, except meters are used instead of inches.
Republic of Korea
Korea also uses the Jin Yong-han or Han Chun-suck chart which is similar to the Snellen chart except the first row which has the biggest letter starts at 0.1 and goes up to 2.0 which has the smallest letters. These charts use Korean letters, numbers and pictures. In the end, you would get a number for your left eye and right eye. For example, if you get 1.0 for left and right eye on the eye test, you would fall in the average.
Typical procedure for vision scoring:
1.First you will be lead into a room and then cover one eye (this can be with an instrument the clinic gives you or simply just using your hand) and stand at a fixed distance.
2. You close in on the distance until you can identify the letters that starts from the row 0.1 (biggest letters).
3. Doctor will point the letters in each row and downwards until you can no longer identify.
4. Results are provided accordingly.
Simply put, they all use the same concept as the Snellen chart but use different measurements.
It is important to note that the vision scoring results and tests is not the only way in which to evaluate the quality of your vision. Multiple other factors can play a role in how good your vision is.