What do you call the diagram letter commonly used by opthalmologist to test eyes vision?

Question

and where can i download it? thanks alot...

Answer 1

The Snellen letter is used.  Snellen letters are 5' of angle high for 20/20.  This turns out to be 8.9 mm at 20 feet.  Each stroke of the letter is 1' of angle.

20/40 letters would then be 2 x 8.9 x 15 /20 mm high at 15 feet, a common testing distance.  Not all letters are used. Optometrists use Snellen letters for near and for distance.  Ophthalmologists often use Jaeger letters,  J1, J2,  etc. for near.  Jaeger letters do not have exact equivalent sizes.  If a testing distance happens to be 4 meters, minus a quarter

(-.25) is sometimes added to the prescription.

Sometimes a tumbled E is used.  Sometimes when you are working with children it helps if the kid can just make 3 fingers point in the direction of the strokes of the E.  Some of the kids get twisted wrists when they try to line up their fingers to match the Es on the chart.  The Es can be presented in different sizes for a good test of visual acuity.  

Ophthalmologists call it sensitivity.

You can make your own letters or cut them out of magazines now that you know the size.

Snellen letters are plain without serifs.