Astigmatism is a common and usually minor eye condition that causes blurred or distorted vision.
It occurs when the cornea or lens isn't a perfectly curved shape. Many people who wear glasses have some degree of astigmatism.
Astigmatism belongs to a group of related eye conditions known as refractive errors. Other common refractive errors include:
If you have astigmatism, it's likely you'll also have one of these conditions.
Left untreated, astigmatism can cause headaches, eye strain and fatigue (tiredness), particularly after doing tasks that involve focusing on something for long periods, such as reading or using a computer.
What causes astigmatism?
Astigmatism is usually the result of an irregular-shaped cornea or lens. The cornea is the transparent layer of tissue at the front of the eye.
The cornea should be regularly curved like the surface of a football, but in cases of astigmatism it has an irregular curve, more like the shape of a rugby ball. This means that light rays entering the eye aren't focused properly, creating a blurred image.
In most cases, astigmatism is present at birth. However, it sometimes develops after an eye injury or as a complication of an eye operation.
Read more about the causes of astigmatism.
Types of astigmatism
There are two types of astigmatism – regular and irregular.
Regular astigmatism is where the cornea is curved more in one direction than the other. It's more common than irregular astigmatism and can be corrected with glasses or contact lenses.
Irregular astigmatism is where the curvature of the cornea isn't even across the surface of the eye. Instead of being curved mostly in one direction, it could be curved in multiple directions, or the curve could be steeper towards the bottom.
Irregular astigmatism is often the result of an eye injury that causes a scar to develop on the cornea. It can't be corrected with glasses, but it can be corrected with contact lenses.
Astigmatism is usually diagnosed after a routine eye test.
It's very important for you and your children to have regular eye tests because astigmatism sometimes goes undiagnosed for years, and it can affect your or your child's ability to read and concentrate.
Read more about diagnosing astigmatism.
In many cases, the symptoms of astigmatism are so mild that treatment isn't needed to correct your vision. In cases where your vision is significantly affected by astigmatism, glasses or contact lenses can be used to correct it.
In adults, laser treatment can also be used to permanently correct astigmatism. However, it's unlikely you'll be able to receive laser treatment through the NHS.
Read more about treating astigmatism.