We've all run into the terms twenty-twenty vision and visual acuity. Yet, what do these terms truly mean?
The term 20/20 vision is used to indicate the sharpness of vision measured at a distance of 20 feet. If you've been told you have 20/20 vision, that basically means that from 20 feet away you are able to accurately see what should be seen from that distance. Alternatively, 20/100 eyesight would indicate that you'd need to be as near as 20 feet away to see what a normal-sighted person is able to see from 100 feet away. Obviously, in this scenario, you would be very near sighted.
Both eyes are tested one after the other. When the optometrist asks you to look at the eye chart and read out the letters, the smallest row that you can read properly determines the visual acuity in the eye being examined.
But 20/20 sight doesn't necessarily mean that your eyesight is perfect, and that's because it can only judge your clarity of vision at a distance. There are lots of equally necessary sight skills; being able to focus on close objects, contrast sensitivity, peripheral awareness, depth perception, eye coordination and color vision - these also contribute to your overall ability to see. More importantly, someone with 20/20 vision can have unhealthy eyes. Those with damage to the nerves within their eyes due to diabetes, high blood pressure, glaucoma, or a range of other diseases might still have 20/20 vision, without the help of glasses. This is why an optometrist will always carry out a comprehensive eye exam, rather than just a simple visual acuity test.
When you're having your next eye exam, you'll understand what we're looking for when we ask you to read letters aloud from an eye chart!