Astigmatism and Contact Lenses

Astigmatism is caused by an irregularly shaped cornea (called corneal astigmatism). But sometimes it is the result of an irregularly shaped lens, which is located behind the cornea. This is called lenticular astigmatism. Either kind of astigmatism can usually be corrected with eyeglasses, contact lenses or refractive surgery.

In fact with modern contact lenses, astigmatism and contact lenses do go together. Consult further information on this site and your contact lens specialist.

If you have only a small amount of astigmatism, you may not notice it or have just slightly blurred vision. But sometimes uncorrected astigmatism can give you headaches or eyestrain, and distort or blur your vision at all distances.

Children may be even more unaware of the condition than adults, and they are unlikely to complain of the blurred or distorted vision.

Astigmatism occurs when the cornea is shaped more like an oblong football than a spherical baseball, which is the normal shape. In most astigmatic eyes, the oblong or oval shape causes light rays to focus on two points in the back of your eye, rather than on just one. This is because, like a football, an astigmatic cornea has a steeper curve and a flatter one. In regular astigmatism, the meridians in which the two different curves lie are located 180 degrees apart.

Regular astigmatism is usually easy to correct, but irregular astigmatism can be complicated and more difficult to correct, depending on the extent of the irregularity and its cause.

Here, two portions that are opposite to each other are blurred because of the oblong shape of the cornea.

Usually astigmatism is hereditary: many people are born with an oblong cornea, and the resulting vision problem may get worse over time.

If your eyeglass or contact lens prescription contains three parts rather than one, your eyecare practitioner has found some astigmatism in one or both of your eyes.

The first part indicates your main spherical correction, meaning the amount of power (in diopters) required in a lens to sharpen your visual acuity to an acceptable level, usually 20/20.

In this example, the person has myopia and requires a negative (concave) lens to correct it.

Part three is the axis (in degrees) of the cylinder required to bend certain light rays to compensate for the cornea's oval shape.

Many people with astigmatism believe that they can't wear contact lenses, or that only rigid contact lenses (RGPs, also called GP lenses) can correct astigmatism. This is not now the case. Many forms of astigmatism can be corrected using special toric contact lenses.