Question

A person standing 20 feet away from the Snellen chart can read only the line that should be able to be read by a person with emmetropia at 200 feet. Calculate this person's visual acuity (show your work).

Answer 1

Emmetropia is the ideal condition of eyes. Emmetropic eyes can ideally focus the image on the retina. When both eyes of a person are in the emmetropic condition the person's vision is said to be ideal.

A Snellen chart refers to the eye chart which is used by the ophthalmologists to check visual acuity. It generally has 11 lines of block letters having different sizes in a grid arrangement.

In the given condition, a person is able to see a line at 20 feet which he should be able to see from 200 feet with normal or emmetropic eyes. Visual acuity can be calculated by dividing the distance that the person seeing the object clearly by the distance it should be seen with normal eyes. Hence, in this case, visual acuity will be 20/200 or 0.1. It can be converted for 10 feet or 6 feet based on its decimal value or fraction such as for 10 feet it will 10/100 and for 6 feet it will be 6/60.