Snellen Chart

The chart is intended to be used at a distance of 20 feet (about 6 meters) but can be closer if reading difficulties are presented. The person tested must open one eye at a time. The examiner randomly select letters on each row and notes the right and wrong answers.

The score per eye is the result of the distance divided by the value of the smallest line read correctly.

The Snellen scale uses different letters depending on the country, the principle is that they are quite easily discernible.

In the original version, the letters were

A,C,E,G,L,N,P,R,T,5,V,Z,B,D,4,F,H,K,O,S,3,U,Y,A,C,E,G,L,2

But can be different and suitable for any type of audience.

Example: C,D,E,F,L,O,P,T,Z in the above image

The size of the letters decreases on each row which makes it possible to evaluate with a fraction or a decimal number the most value read by a person tested.

Snellen created it in 1862.