KASHSURG Snellen's Distance Vision Eye Chart 20 Feet- Pack of 1 Vision Test Chart  (Snellen)

These Snellen Eye Chart was originally introduced in 1862 by Herman Snellen. The Snellen eye Test uses the idea of subtended 5 minutes of arc with a 20 Feet distance. This became the "Standard Vision" measurement. Also, Snellen developed the idea of a 5 x 5 grid for a standard for his optotypes. Each Optotype must meet certain percentage requirements in this grid before it is used for testing. This helps to make a uniform and equal vision chart. The Snellen eye test is the basic many other vision tests