Dr. Param Jit Singh
Do you know what a 20/20 vision means or 6/6 for the matter?
Surprised? And why feet?
Americans love their imperial system so is it feet and 20/20 for them.
Most of the world has moved on to use meters so it is 6/6 for them. UK still has lot of love for their feet and inches, but Europe didn’t have any of that and they became 6/6 as well. It means the same thing though.
It is reasonably accurate way to measure your distance vision- known as Visual Acuity to test how well and from how far you could see but like everything else in life things has moved on and there are other ways to measure what power of lens you might need to correct your vision.
A chart known as Snellen with the biggest letter at the top is used to test for distance vision and a smaller handheld chart is used for near vision.
But there is more to eyesight than just the visual acuity.
There is peripheral vision, eye coordination, depth perception, focusing ability and colour vision. There is Eye-Hand co-ordination but that is little different.
So, what does 20/20 or 6/6 means?
Stop, have few guesses, and then read on.
20/20 means you-the person being tested, can see clearly at 20 feet (6 m) what should normally be seen at 20 feet (6 m). Mostly it is the 8th line from the top. If you can read that at 20 feet you have 20/20 vision.
Now if you can read only the top letter but nothing smaller below on the Snellen chart than you have 20/200 (6/60) vision and that means you see from 20 feet what a person with 20/20 vision can see from 200 feet and you are considered legally blind though now terms like visually impaired or visually handicapped are used more often.
And 20/40 (6/12) means you can see at 20 feet clearly what a 20/20 vision person can see at 40 feet and so on.
Now there are people who have better than 20/20 vision i.e., 20/10 (6/3) means they can see at 20 feet what a person with normal vision is seeing at 10 feet.
There are other ways of testing and measuring what a person is capable of seeing if they cannot even see the top line, like -brining the chart closer to the patient but if they cannot read at even 1 meter than they are asked to count fingers at certain distances, failing that if they can see shaking of the hand movements at certain distances and if they cannot then if they can tell which direction the light is coming from called projection of light or if they can perceive light at all.
So, 20/20 is normal visual acuity and No light perception is considered as total blindness.
Thus it might be worth learning ’20-20-20” rule to protect your eyesight and have less eye fatigue. This is about looking at something 20 feet away for 20 seconds, every 20 minutes you look at a screen. This helps relax your eye muscles and prevent eye strain.
About the Author: Dr. Param Jit Singh
"I am a retired medical doctor who worked as a General Practitioner in England for over 40 years. My practise has always been to pass on the best advice to my patients that will improve their wellbeing, often in a written format so they can keep and refer back to it.
Sometimes this advice is based on previous medical experiences but it can also come from medical books, current government approved medical guidelines and protocols or as advice articulated by other doctors.
I do not claim that every line of this article is my original work but it is put together here by me in this format so that it is concise, easier to understand and follow and can help you improve your knowledge and wellbeing too."