Astigmatism is an imperfection in the curvature of your eye’s cornea or lens.
It may be helpful to think of the normal eye as being shaped like a basketball. With astigmatism, it's shaped more like an American football. When the steepest curve runs vertically, with the football lying on its side, it's called:
- with-the-rule astigmatism
When the steepest curve runs horizontally, with the football sitting on its end, it's called:
- against-the-rule astigmatism
Two types of astigmatism
Normally, the cornea and lens are smooth and curved equally in all directions. This helps to focus light rays sharply onto the retina at the back of your eye. If your cornea or lens isn't smooth and evenly curved, light rays aren't refracted (bent) properly. Doctors call this a refractive error.
When your cornea has a distorted shape, you have corneal astigmatism. When the shape of your lens is distorted, you have lenticular astigmatism. In either case, your vision for both near and far objects is blurry or distorted. It's almost like looking into a fun house mirror in which you can appear too tall, too short, too wide or too thin.
People may have astigmatism along with other refractive errors, such as:
Adults with significant astigmatism may realize their vision isn't as good as it should be. Children with astigmatism symptoms may not be aware they have this condition. They are unlikely to complain about blurred or distorted vision.
In a normal eye, the cornea and lens focus light rays on the retina.
In astigmatism, images focus in front of and beyond the retina. Close and distant objects both appear blurry.
Uncorrected astigmatism can impact a child's ability to achieve in school and sports. It is crucial that children have regular eye exams. Get these exams to detect astigmatism and other vision problems as early as possible.
What causes astigmatism?
Astigmatism is caused by an irregular curvature of the eye's cornea or lens. If your cornea or lens isn't evenly curved, light rays aren't refracted properly. With astigmatism you have blurred or distorted vision at near and far distances.
Astigmatism is very common. Doctors don't know why corneal or lens shape differs from person to person. They do know that likelihood of developing astigmatism is inherited.
Astigmatism can develop after an eye disease, eye injury or surgery. It is a myth that astigmatism can develop or worsen from reading in low light or sitting very close to the television.
Astigmatism symptoms may include:
- blurry vision or areas of distorted vision
- squinting to try to see clearly, or
- eye discomfort
If you have these symptoms you may not necessarily have astigmatism. You should visit to your ophthalmologist. A complete eye exam will determine what is causing your symptoms.