Astigmatism is a refractive error usually caused by an irregular curvature on the surface of the eye. As light enters the eye it is focused on two points instead of a single point needed for clear vision. Normally the curve on the surface of the eye is equal from left to right and from top to bottom, giving the surface of the eye an equally round shape like a ball.
With astigmatism one of these curves is elongated making the surface of the eye oval shaped. This could, for instance, cause the light being refracted by the horizontal axis of the cornea to focus on a different point than the light being refracted by the vertical axis.
This causes two points of focus instead of one. If the points are focused before the retina the astigmatism is considered nearsighted or myoptic. If the points are focused past the retina it is considered farsighted or hyperoptic.
Symptoms of astigmatism include headaches, eye strain and fatigue. Severe astigmatism can cause a blurriness of images at all distances, while milder cases may cause blurriness only at certain distances. If you suspect you are suffering from astigmatism, ask your doctor for advice. Successful corrective measures include contact lens or refractive surgery.