What exactly does 20/20 vision mean?

Having a son-in-law who is legally blind has given me an appreciation for my eyes, even though they are far from perfect.  As a result of research about my son-in-laws vision problems it lead me to learn some very interesting facts about eyes and the history of vision.

If you see things 20/20, you have almost perfect eyes and can see the world better than most!   But if you live in other parts of the world other than the United States you would need 6/6 vision!  20/20 vision means that you have good vision when you at 20 feet.  In the metric world, which is most of the world, the same measurement factor is six meters instead of 20 feet! 

Snellen Eye ChartCredit: elderlydrivingassessments.com

When you go somewhere to have an “eye test” they will use the “Snellen chart” to test your vision.  A Dutch ophthalmologist developed a chart in 1862 to determine the vision of his patients.  Dr. Hermann Snellen, developed the traditional “eye” chart that has 11 lines of block capital letters, beginning with a single letter at the top, usually an E.  The size of the letters gets smaller from the top of the chart to the bottom, so there are more letters on the bottom row than on the top.  The eighth row of letters is usually the line for 20/20 or 6/6 vision. 

Sixty-one percent of Americans wear corrective lenses to have “normal” or 20/20 vision.

Many people wonder if all of the letters of the alphabet are on the chart.  No, they aren’t.  The letters used are C, D, H, K, N, O, R, S, V and Z with the letter E on the top.  These are Sloan letters, designed by Loui

s Sloan in 1959 and are called “optotypes.” 

Are baby eyes the same size as adult eyes?  No.  A baby’s eyes are only about 75% of the size of adult eyes when they are born.  The optic nerve, internal eye structures and visual function continue to develop in the first two years of life.

Each component of the eye has a special function, and together the components are important and needed

for good vision.  Eye professionals have had to spend a lot of time learning how to “fix” vision and eye problems and even then they haven’t been able to cure or correct all problems.

What would it have been like before they could do the corrective actions they can take today such as eyeglasses, contacts and surgeries? 

The Chinese claim to be the inventors of the eyeglasses but only used them initially to ward off evil spirits.  They wore eyeglasses for protection and they more than likely did not improve the vision. 

Eye GlassesCredit: liveauctioneers.com

No one knows for sure who actually invented the first eyeglasses that were used to improve vision.

The first time eyeglasses were seen in artwork was a painting by Tommaso da Modena in 1352.  The glasses in this painting were set on the nose of his subject even though the early eyeglasses that actually corrected vision were not of this style.  The glasses that in reality helped correct vision problems; monocles, scissors-glasses and lorgnettes were either worn around the neck on a ribbon or chains, clipped to clothing or were just hand held. 

Eyeglasses then progressed to the “pince-nez” style.  These were two-lens glasses that pinched the nose in order to stay on.  The name comes from the French words – pincer or to pinch and nez which means nose.  They were in frames and attached to a cord, ribbon or chain to keep the owner from losing them.

Edward Scarlett, a London optician, perfected the use of sidepieces or arms that attached to lenses in 1730.  His new style that slipped over a person’s ears eliminated the need for chains or ribbons, freed up the hands.  They quickly became popular and spread worldwide. 

Contact lenses are not as new and you may think.  The idea goes all the way back to the late 1800’s when a glassblower named F.E. Muller, a German eye glass maker, blew a protective lens for a man who had cancer.  The patient wore the lens for 20 years until he died without losing his vision.  The term of “contact lens” actually came from Dr. A. Eugen Fick, a Swiss physician who published the results of his experiments lenses in 1887.

What kind of eye doctor should you go to?  We often are not sure what type of eye professional we need to visit for eye problems.   Here are the main duties of the most common eye professionals: 

  • Opticians – Manufacture and dispense glasses and contacts.  They will often deal with patients after they have seen an optometrist or ophthalmologist.
  • Optometrist – A vision professional who can diagnose vision problems, prescribe contacts and eyeglasses, provide treatment before and after eye surgery and prescribe drugs for various eye problems.
  • Ophthalmologists – An ophthalmologist is a licensed medical doctor and can do everything performed by optometrists plus they can perform eye surgery because they must complete four years of medical school following a college degree and an internship that focuses on their desired specialty.

 Many animals have vision that is far superior to humans.  The giant squid has the largest eyeballs on the earth.  Imagine the size of a beach ball of about 18 inches in diameter and you can visualize the size of the giant squids eyeballs. 

Giant SquidCredit: file770.com

The Ostrich have the largest eyes of any land animal, measuring about two inches across.  Ostrich eyes are actually larger than their brains, which are about the size of a walnut!

If someone tells you that you are “blind as a bat,” don’t take offense.  Bats are not blind, but they don’t use their eyes to see.  They use sound waves instead. 

Have you ever been told you have “eagle eyes?”  If so, you must have great vision!  An average person can see a rabbit at about 550 yards, while an eagle can see it at about one mile or 1,760 yards! 

Having our vision is something we should treasure.  You should do everything you can to protect your sight so that you can enjoy seeing the world around you because not everyone has this blessing in life.