Astigmatism

Astigmatism is a focusing error of the eye whereby the light entering the eye does not form a point focus on the retina. In other words, there is asymmetric blur with some directions in an image being more out of focus than others. This is in contrast to both myopia and hyperopia, where the light does form a point focus, however this point focus is in front of the retina for myopia (causing distance objects to be blurred) and behind the retina for hyperopia (causing near objects to be blurred). Consequently, with myopia and hyperopia all directions in an image are uniformly blurred.

Astigmatism is generally due to the shape of the cornea (the front surface of the eye). Normally the cornea's curvature is the same in all directions (like a soup spoon) but sometimes it is steeper in one direction than another (like a dessert spoon) and this causes the astigmatism. Less frequently, astigmatism may be due to irregularities in other components such as the lens and the retina of the eye.

Astigmatism usually leads to difficulty in seeing fine detail as well as eyestrain and headaches if the degree of astigmatism is high and it can be corrected by spectacles or contact lenses. With respect to the latter, it used to be a commonly held belief that you could not be fitted with contact lenses if you had astigmatism. This is definitely no longer the case. With the advances in contact lens technology over the past ten years, the visual requirements of most astigmatic patients can be readily satisfied with contact lens correction. Contact lens options for correcting astigmatism include soft lenses, rigid lenses and hybrid lenses.