What is Astigmatism?

Not all eyes are perfect circles, sometimes they are more oval shaped. If a person has an irregular shape or curvature of the cornea (the clear part that covers the surface of the eye) or lens inside the eye then it results in an astigmatism which is quite common. In a round eye, or in an eye without astigmatism, the cornea and lens allow the light to focus at a single point on the retina. If there is an astigmatism, then the cornea or lens is more elliptical which causes the light either to focus before or after the retina. It is common to have astigmatism along with other vision conditions such as nearsightedness or farsightedness. Together, these vision conditions are called ‘refractive errors’ because they affect how the eyes bend or ‘refract’ incoming light. People with astigmatism tend to require a more specific prescription for glasses or contact lenses which allows light to bend properly on the shape of their eye. There is an added component of a prescription for glasses or contact lenses called the cylinder, which is customized to correct an astigmatism.

Causes of Astigmatism

Astigmatism is generally a condition people are born with and is inherited. It can also be developed due to an eye disease, injury or surgery. Astigmatism can be caused by a degenerative eye disorder called keratoconus which is when the cornea (the clear part that covers the surface of the eye) becomes thinner and more cone-shaped.

There are two types of astigmatism, each with their own cause due to the anatomy of the eye:

1. Corneal astigmatism - this is the most common type and it’s a result of an irregularly shaped cornea. The cornea is a clear layer which covers the surface of the eye and contributes greatly to the way we see.
2. Lenticular astigmatism - this type is caused by an irregular lens inside of the eye.