WHAT IS VISION 20/20?

If you wear glasses, or even if you don’t you probably have atleast heard of 20/20 vision i.e (6/6). But despite this ,few people really know what exactly it means.

So What is Vision 20/20?
DEFINITION:
At 20 feet or 6 meters ,a human eye with nominal (normal ) performance is able to separate contours that are approximately 1.75 mm apart.(From Wikipedia)
In simple language you can say that 20/20 vision is the term used for what a person ,who doesn’t require glasses ,should be able to see clearly at a distance of 20 feet away from the person.
The chart used was likely a Snellen Chart for the vision screening .
Snellen Chart
Named after the Dutch ophthalmologist Herman Snellen who develop the chart in 1862.
Basically what Mr Snellen concluded is that if the visual system can recognize a letter this small at a distance of 20 feet(6 meters) that person has 20/20 vision.6/6 vision is the metric equivalent to 20/20.
Most of us are familiar with this chart over here.

Screenshot 20200622 233416 01 01

Now it’s certainly not the only chart that’s out there but it is the most common while there are a lot of different vision charts out there.What happen is that at 20 feet we try to read the smallest letters you can whichever row you can read upto .

Screenshot 20200622 233416 01 01 01 2

So let’s say in this case 8 you have visual performance correspondence with the number on the right .So you can Read upto line 8 you have 20/20.

The standard viewing distance is 20 feet (6 meters) .Some of you might be thinking about the last time you had your eyes examined and if the exam room was whether 20feet(6metres) long.The truth is every exam rooms are less than 20feet but there are ways around this optically with mirrors.
The next time when you have your eye being examined, look on the walls and you will likely see a mirror .When you sit down and and you can observe the chart ,the chart you are looking at is likely seen through a mirror.The chart and the mirror are precisely calculated so that the chart appear 20 feet away.

Why is it called 20/20???

First 20 represents the distance of 20 feet (6m) that you are going to look at and second 20 represents the distance that a person with 20/20 vision would be able to read same as you.


However if a person has 20/30 vision ,they will only be able to see clearly at a distance of 20 feet away, what a person with 20/20 vision would still be able to see clearly up to 30 feet away.
Similarly ,
20/80 vision ,they will only be able to see clearly at a distance of 20 feet away ,what a person with 20/20 vision would still be able to see clearly up to 80 feet away.
20/200 vision is considered to be legally blind.

20/20 vision is often perceived to mean “perfect vision” although 20/20 vision is the normal vision without glasses but this is not the case and some people have been also known to have 20/15 or 20/10 vision.

A person with these visions would be able to see clearly at 20 feet away,what a person with 20/20 vision would only be able to see clearly at distances of 15 feet away and 10 feet away respectively.

Finally even if you have 20/20 vision ,it doesn’t mean that you have perfect vision. You do need to see an eye doctor because there is much more visit to eye doctor than just seeing 20/20 .During your visit, your optometrist will evaluate three key areas, in which first includes vision check ,next is your binocular ability and lastly your eye health.
Vision check includes 20/20 examination which evaluates how well you can see.
Binocular ability involves evaluating your two eyes work together as a team .Binocular weaknesses can have severe impact in eye such as eye strain . People who suffer from binocular weakness may have no idea of having problem ,yet may have issues such as sore eyes ,tiredness .
Eye health check is for some diseases such as glaucoma ,cataract,and macular degeneration.These disease often lead to blindness if not treated in time.
Therefore even if you have 20/20 you need to visit your optometrist, ophthalmologist regularly in at least span of 6 months and have your complete eyes checkup.

MONIKA MANDAL

VISION SPECIALIST

One thought on “What is Vision 6/6 ? (Normal Vision) (20/20)

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