85-90% of all eyeglass prescriptions contain some correction for astigmatism. The eye, like a camera, has an outer curved lens, the cornea, to focus light. Most commonly, astigmatism occurs when simply this front surface has more than one curvature, rather than a perfectly round shape. With astigmatism, the shape of the cornea is asymmetrical, or somewhat “egg” shaped, rather than uniformly round like a ball. As a result, an astigmatic eye requires a special two-power lens to precisely focus light uniformly.
Since astigmatism causes two different focuses per eye, and especially if astigmatism exists in both eyes, the brain has much to contend with. As a result, uncorrected or incorrect prescriptions for astigmatism cause blurred and distorted vision, as well as, annoying symptoms of eyestrain such as headaches, eye fatigue, sensitivity to light, loss of visual achievement and poor visual concentration.
It is expected that first correction or large changes in correction of astigmatism may cause objects or straight lines to appear tilted or distorted. This perception of distortion will decrease steadily with time. As with most prescriptions, it is common for the degree of astigmatism to change naturally over time. Eyeglasses, and/or, special astigmatic (toric) contact lenses are available to correct astigmatism.