What exactly is astigmatism.?

Question

is it the shape of the eyeball, like chinese eyes are long sort of, and sometimes british's are rould, etc. Is it the shape or is it the eye itself?

Answer 1

astigmatism is when you can't see as well as you could, i think.

Answer 2

It's nothing to do with shape of the lids, and it's nothing to do with having an irregular cornea.

(there's even a condition "irregular astigmatism" to cover those circumstances where that doesn't hold.)

It's only a particular version of short or long sight, as liable to change or stay the same as any Rx.

Astigmatism specifies the amount by which one Rx number doesn't focus the eye perfectly in every meridian, and notes the direction in which the extra amount has to be applied.

So, if the Rx was -3.00 / -1.00 ax 180, an eye looking at the letter E in the distance through the -3.00 DS only would see the vertical stroke clearly, but the horizontal arms would be blurred.  An extra -1.00 is required but only affecting the blurred direction, other wise the part already clear would be spoiled.  

The third number is an orientation in degrees ( 1-180, 90 vertical, 180 horizontal) because the direction can have any inclination.  In this respect 5 is not worse than 175: its' just a direction.