Astigmatism

Blurry vision. 

Astigmatism is when the cornea is badly curved in particular zones.

Normally, the cornea of the eye is not curved evenly, like a ball, but has vertical and horizontal curvatures, which are exactly matched. This way, light from the side, top or bottom reaches the retina as exactly as light coming from the front.

If the curve of the cornea is greater or less than it should be in one or more areas, the incoming light will be irregularly refracted and unevenly dispersed in the different meridian directions with astigmatism.

"Muscle-ache" in the eye?

With astigmatism the eye makes a continual effort to compensate this refractive error by use of tiny muscles. This sustained effort with astigmatism can occasionally lead to headache.

It can be hard to adapt to glasses with astigmatism.

A first-time adaption of cylinder glasses to correct astigmatism in adulthood is often problematic. Although they can offer clearer vision, strong glasses feel unusual to adult eyes, and often result in headaches. Because of this, adults who need cylindrical glasses for the first time often take a weaker lens. The strength of the lens to correct the astigmatism is then gradually adjusted.