What Is 20/20 Vision? How Convert Diopters To 20/20 Scales

What is 20/20 vision?

You can't help but... with 20/20 hindsight, go back and say, 'Look, had we done something different, we probably wouldn't be facing what we are facing today.' - Norman Schwarzkopf


20/20 vision is like the ultimate goal for many people’s quest for better eyesight. Chances are you had seen LASIK advertisements promising 20/20 eyesight.

In fact 20/20 vision is so prevalent in our society that they have an American TV show called 20/20.

But what is 20/20? 


The Snellen Eye Chart

Snellen Eye Chart

Before we go there, let’s understand what visual acuity means. Visual acuity means sharpness of your vision or how far can you see.

During your school days or work requirements, you probably had been tested on the 20/20 scale before. 

Most eye doctors use a standardized eye chart (usually Snellen eye chart named after Herman Snellen, the Dutch ophthalmologist who developed this measurement system in 1862.) to determine your visual acuity.

Chances are you have already assess with this method before.

The Snellen eye chart is made up of capital letters and 11 rows.

It usually starts with a big E at the top, the letters become progressively smaller as it reaches the bottom rows.

Usually, your eye doctor will require you to stand 20 feet away from the chart.

However, as most of offices are too small, mirrors are used to simulate 20 feet instead.

During the test, your doctor will try to assess smallest imprint which you can see accurately.

People with normal eyesight will be able to read up to row 8 which is equivalent to 20/20 vision. 

A person with 20/100 vision will mean that he can only see clearly an object at 20 feet where other with normal visual acuity can see at 100 feet

In some countries, it is measured in metres instead. As such, the normal eyesight is equivalent to 6/6. 

In nutshell, 20/20 the visual acuity of someone with healthy eyesight.


Having 20/20 Vision Isn't Everything

However, just measuring visual acuity does not accurately assess how well you see.

As mentioned previously, 20/20 acuity is a simple measurement of distance visuality and there are many other factors to take into account. 

Good vision consists of efficient eye coordination, accurate perception of depth and color and focusing ability.

It also include peripheral awareness, also known as side vision.

Tunnel vision will allow you to read those eye charts at 20 or even 30 feets but being unable to see from your side glance definitely means something is wrong.

It doesn’t measure other possible conditions such as eye fluid pressure (which may cause glaucoma if too high), glare, involuntary rapid eye movement and etc.

As such several tests may require to assess your true eye health condition and whether there is any occurring eye disease. 




Is It Possible To Have Better Than 20/20 Vision?

Previously, many people thought that only animals (eagles have natural vision of 20/2) have vision better than 20/20.

However, studies had proven that it is possible for humans who can reach have better than perfect vision.

According to a study published in American Journal of Epidemiology, an unnamed Australian Aborigine man has a visual acuity of 6/1.5 (equivalent to 20/5 vision) . 

The secret of his superb vision? 

The studies reported it is partly genetics and partly due to him using his distance vision a lot.

Yeah tons lot as compare to we office dwellers.

There are often records of European colonists where Aborigines told them they spotted a whale on the horizon and the European thought they were lying.

Therefore, having 20/20 is merely the average visual acuity for a healthy human being and there is nothing which stop us from gaining better than 20/20 vision.

In fact, some fighter pilots use eye exercises to attain 20/10 vision. 


How to Convert Diopters to 20/20 Scale?

Now you have understood what 20/20 vision means, it does not translate to the prescription that your optometrist will pass to you for your glasses.

While the 20/20 vision system measures how well you can see compared to a healthy benchmark, diopters measure the focusing power of your glasses.

The prescription is measured in diopters, the refractive power of your new glasses or contacts.

You will get a separate diopter value for each eye. If the measurement has a minus (-) before it, you are myopic and if there is a plus (+) before it, you are hyperopic.

There is a relationship between the two, shown in the table below. 

20/20 Measure In Feet 20/20 Measure in Metres Estimated Refractive Errors in Diopters
20/20 6/6 0
20/30 6/9 -0.50
20/40 6/12 -0.75
20/50 6/15 -1.00
20/70 6/20 -1.25
20/100 6/30 -1.50
20/150 6/45 -2.00
20/200 6/60 -2.50
20/250 6/75 -3.00
20/300 6/90 -3.50
Diopter Conversion Chart

The right-hand column is given approximately as there is not a rigidly fixed relationship between refractive error and visual acuity.

Two people who have the same refractive error and need the same prescription may have widely different degrees of success in reading a distant wall chart with their glasses removed.

This chart is based on the average of many people and cannot be used for accurately predicting either the visual acuity or the refractive error of any particular individual.

It is included here merely for information purposes.


Related Readings:

› What Is 20/20 Vision?