The cornea of the eye astigmate (short-sighted astigmate or hypermetrope astigmate) is deformed.
Instead of being spherical, it is bent in a direction (for example vertically) that in the other (for example horizontally).
TO INCLUDE/UNDERSTAND the ASTIGMATISM
In the astigmatism the eye sees more distinctly in a direction than in another. Thus the second image is stretched horizontally whereas the third is vertically.
It results from it that a confusion can join the fuzzy vision while making letters close not very different: confusion between N and m, O and C...