What is astigmatism?

Astigmatism occurs when the focusing structures of the eye -- the cornea and lens -- are not perfectly round.

I get this question a lot, and since it's often misunderstood, I thought it would be a great topic to discuss.

Astigmatism, along with the previously-discussed entities of hyperopia (farsightedness) and myopia (nearsightedness), is one of three common types of refractive error. Refractive errors are problems with the focusing system of the eyes.

A normal eye is round, like the baseball you see here. An eye with astigmatism, by contrast, has a cornea -- the clear, front part of the eye that focuses light -- that is steeper/more curved in one axis and flatter in the axis 90 degrees away, like a football. This means that light in an eye with astigmatism is focused at two different points on the retina, creating a blurry image.

Astigmatism, like all refractive errors, can be corrected with glasses, contact lenses, or laser surgery (e.g. LASIK). It is easy to identify in a routine eye examination.