The "20/20 Eye Test" Story

It was an ordinary day.  Sitting in my eye doctor's office trying to read the chart on the wall that hangs about 20 feet from my chair.  Often wondered who every made that chart in the first place and why did they make the letters so small on the bottom few lines.  Is there anyone who can read those letters?  Then I found there is another eye test that is perhaps the world's oldest eye test.  Goes like this...using only the naked eye, spot the second star from the end of the Big Dipper handle which is known as Mizar.  Now if you can't find the Big Dipper, ask someone or check it out online.  After finding the second star from the handle look at the star to the side of it which is Alcor.  They really aren't side by side since they are light years apart, but they appear to be next to each other.  If you can distinguish the two stars separately, you have passed the world's oldest eye test and have approximately 20/20 vision.  

If you can't distinguish two stars you probably need eye glasses to correct your vision.  In 1623 Spaniard Benito Daza de Valdés wrote the first book on optometry and placed mustard seeds at measured distances and asked patients to count them.  Later he used small print to be read at different distances.  The results told him the strength needed to correct your eyesight.  Then in 1843 a German ophthalmologist, Heinrich Georg Küchler created the first eye chart using symbols.  He cut images of animals, farm tools, weapons, etc. and pasted them on a piece of paper arranged from largest to smallest.  He also used a chart of alphabet letters in graduated sizes.   That was a good start, but in 1862 Herman Snellen of the Netherlands designed a type font for the optotypes (letters or figures for testing) in a chart of specifically calibrated letters in 11 rows.  The top row contained the largest letter (E), and each successive row decreased in size.  It was designed to be read from a distance of 6 meters or about 20 feet.  His chart has become an icon at eye doctors offices today.  Normal vision is described as the ratio of 20/20 which is an arithmetical expression of the distance from the chart over the distance from which normal vision can read the chart.  A 20/30 reading suggests problems with vision: only at 20 feet can the individual see what a person with standard vision see at 30 feet;  20/40 vision means that the viewer needs to be 20 feet away from something to see what a normal viewer can see at 40 feet.  A reading of 20/10 indicates that the viewer has higher vision than average; he or she can see at 20 feet what a normal viewer can see only at 10 feet.  If your vision is 20/200 or less, when using eyeglasses or contact lenses, you are considered legally blind, which is not the same as sightless.  About 35% of the adult population have 20/20 vision with the aid of glasses.  It seems that athletes fall into that category most times.  Great archers and sharpshooters have a visual acuity of 20/16.  The best for a human was an aboriginal man who had a visual acuity of 20/5 vision.  About 30% of North Americans have been found to be nearsighted which means then can see relatively close objects clearly while those at a distance appear blared.  This will become worst by 2050 since people spend too much time looking at a TV, computer, etc. screen.  Therefore, I need to stop typing at this point and go see if I can find the Big Dipper!  It was another extraordinary day in the life of an ordinary guy.