Astigmatism is a common eye condition causing blurring or distorted vision.
It occurs when the cornea or lens isn’t perfectly curved. 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:
- short-sightedness (myopia)
- long-sightedness (hypermetropia)
Astigmatism usually occurs in combination with the previously mentioned conditions.
Astigmatism may cause headaches, eye strain and fatigue (tiredness), particularly after doing tasks that require focusing 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, while the lens is a biconcave structure behind the iris. The cornea and the lens are responsible for refracting light entering the eye. Light is bent to be focused on the retina or the back 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.