What is the angle subtended on each letter of the snellen's cha?
Visual acuity test-types consist of a series of letters arranged in lines, each diminishing in size. The breadth of the lines of which the letters are composed is such that the edges will subtend an angle of 1 minute at the nodal point of the eye at a paicular distance. Each letter is shaped such that it can be placed in a square, the sides of which are five times the breadth of the constituent lines. Hence the whole letter will subtend an angle of 5 minutes at the nodal point of the eye at the given distance.
5 degrees
10 degrees
5 minutes
10 minutes
Optics and Errors of Refraction