You’ve probably heard people referencing excellent eyesight by using the term 20/20 vision, but what does this actually mean? It’s actually considered ‘normal’ visual acuity, and it means you can read from 20 feet away a letter that you should be able to read from that distance. Let’s say for example you could read a letter from 20 feet away that most people could only read from 10 feet away, then you would have 20/10 visual acuity, which would be excellent.
So how is this tested? Visual acuity is determined using something called the Snellen Eye Chart, and it’s the standard chart of letters decreasing in size, seen in almost every optometrists’ office.
You will usually be asked to remove any glasses or sunglasses – you can’t really take the test sporting your Oakley sunglasses – and then you will be asked to look at the chart.
The chart should be placed 20 feet away from the person reading it, although in reality most offices aren’t big enough for this, so instead it is placed behind the reader and viewed via a mirror at a simulated distance of 20 feet.
How many letters you can clearly read from this distance will determine your visual acuity. On most charts the very smallest line of letters is 20/5 visual acuity, and then moving up it’s 20/10, 20/15, 20/20 and up to 20/200 at the very top. So if you can read all the letters of the fourth line from the bottom, you have 20/20 vision. If you could only read the top ‘E’ (the largest letter, which is usually the letter E), you would have 20/200 visual acuity, which is very poor.