Why is the astigmatism test designed like this

Question

I've recently been to the optometrist (my prescription hasn't stabilized yet) and he projected two identical images of shapes and letters on the wall. One image's background was green, while the other was red.

I asked him what it was meant for, and he said It's designed to test astigmatism.

I was just wondering, how does this work? What would an astigmatic person see, and what would a normal sighted person see?

Answer 1

U shd actually try the softlen toric lenses. it is one of the better toric lenses that offers the crisp sharp image all day long

Answer 2

This test really isn't used to test astigmatism.  This is called a red/green balance test.  It is based upon the phenomenon of chromatic aberration.  White light coming into the eye is actually separated into its separate colors when it falls on the retina.  Red, Orange, Yellow, Green, Blue, Indigo, and Violet.  If you are looking at the projected image and you see the image on the red or green side as being clearer or more vivid, then that means you are slightly under or over corrected.  By finding a lens that balances the clarity of the images on the red and green side, the optometrist can be assured that the prescription he has found is as precise as possible for your eyes.