Astigmatism refers to a condition of the focusing system, wherein the focus point of the eye is in more than one place. This condition blurs and distorts both distant and near vision.
If you have astigmatism, often your cornea (the front window of the eye) is shaped more like the back of a spoon, curved more in one direction than in another. Light rays have more than one focal point and focus on different areas of the retina whereas a normal cornea is round with even curves from side to side and top to bottom.
In the general population, most eyes have a small degree of astigmatism and this has little effect on the vision.
If your spectacle prescription shows any number with either a plus or a minus sign in the ‘cyl’ box you have an astigmatic eye eg. +3.50 with regard to astigmatism ('cyl' box) low levels are considered to be up to 1.5 dioptres whereas moderate to high astigmatism is more than 1.6- 3.0 diopters.