If you ever visit an eye specialist’s clinic then you will notice the eye chart that is displayed prominently. Most of you must have undergone eye test at least once in your life time where you were asked to read the letters written on them. This chart has been in use since centuries.
You must be curious to know how any eye exam near me can use this eye chart to test my vision as this method is still followed by the eye clinics.
What is 20/20 vision?
Before we proceed further it is important to understand what we actually mean by 20/20 vision? Well, it means how many of the letters in different sizes can you read standing at a distance of 20 feet. Any person with normal vision can see and read all the letters clearly. In case you have any eyesight problem then your visual acuity can be 20/100. This means that the smallest letter of the chart that you can read from 20 feet distance can be read by any other person with normal vision from 100 feet.
How the eye chart work?
Centuries ago, people have used their scientific mind to create this kind of chart for checking the eyesight. The eye chart that most commonly used in the USA is called Snellen chart. This chart has been named after Hermann Snellen, who was a well-known Dutch ophthalmologist who invented it during 1800s. This chart starts with a single large letter ‘E’ at the top. Subsequently each letter below is reduced until the letter become so small that only a person whose vision is better than 20/20 can read it clearly. The size of the letters is very precisely calculated.
The letters of the chart are also chosen very carefully. If you visit any eye clinic and observe the chart you will notice that all the alphabets of English language are not present in the chart. Only letters used are C, D, E, F, L, O, P, T, Z and rest of the letters are missing. It was discovered that those letters can be detected by our brain even if they are blurred and hence it will not help to check the eyes.
As an example, the letter ‘Q’ which is almost similar to letter ‘O’ however our brain can easily detect the shadow of the tail used in the letter Q and identify it.