Astigmatism is a condition in which your eye, especially your cornea or the clear front part of the eyeball, isn’t completely round.
Ideally, an eyeball is shaped like a perfectly round ball. Light comes into it and bends evenly, which gives you a clear view. But if your cornea is shaped more like a football, light gets bent more in one direction than another. That means only part of an object is in focus. Things at a distance may look blurry and wavy.
It’s common to have astigmatism along with nearsightedness (myopia) or farsightedness (hyperopia). These three conditions are called refractive errors because they involve how your eyes bend (refract) light.
Astigmatism is fairly easy for an eye doctor to fix with glasses, contacts, or surgery.
Most people are born with it, but experts don’t know why. You can also get it after an eye injury, an eye disease, or surgery.
Rarely, a condition called keratoconus can cause astigmatism by making the clear front part of your eye (your cornea) thinner and more cone-shaped. You’ll probably need contacts (but not glasses) to see clearly.
You can’t get astigmatism from reading in low light or sitting too close to the TV.
Astigmatism symptoms come on slowly. Go to an eye doctor if you notice changes in your vision. You’ll need a complete eye exam. Your doctor will test the sharpness of your eyesight by asking you to read an eye chart. They’ll also use tools to measure your vision, including:
Phoropter. You look through a series of lenses to find the ones that give you the clearest vision.
Keratometer. This machine measures the bend in the center of your cornea. It finds the steepest and flattest curves. The measurements tell your doctor about the shape of your cornea and how well it can focus.
Autorefractor. This device shines light into your eye and measures how it changes as it bounces off the back. This gives your doctor an idea of which lenses you need.
Corneal topographer. This technology gives the most detailed information about your cornea’s shape. The doctor tells you to look at a specific point. Meanwhile, the device collects thousands of tiny measurements. A computer builds a color map of your cornea from the data. Your doctor will refer to it if they plan surgery for astigmatism or cataracts. They might use it to fit contacts. It can also help diagnose keratoconus.