Last Updated: October 28, 2016
If you catch yourself squinting at the television, driving slowly at night, or wondering why your image looks distorted in the mirror, astigmatism may be the culprit.
Astigmatism is a common eye condition that causes blurred vision at distances close and far. It happens when the cornea (clear front surface of the eye) or lens (a clear structure inside the eye) has an unusual shape.
Like a camera, your eye must focus all of the light rays that enter your eye from different directions down to a single point in order to create a clear picture. Normally, this happens as light passes through the curved surfaces of the cornea and lens. When these surfaces are evenly curved (like the surface of a ball), they refract (bend) the light rays and focus them on the retina, a light-sensing organ at the back of the eye. (The retina then converts the light patterns into electrical signals, which are sent to the brain via the optic nerve and interpreted as the “picture” we see.)
In reality, almost no one has a perfectly shaped cornea or lens. Steep or flat spots bend light in irregular ways, causing images to focus in front of and behind the retina. This is called a refractive error, and the result is blurry or distorted vision.
Astigmatism sometimes happens alongside other refractive errors, including:
Astigmatism can cause eyestrain, leading to headaches and eye discomfort. Children with astigmatism often don’t realize their vision is abnormal, which can cause them difficulties with school and sports.
In most cases, the exact cause of astigmatism is unknown. The tendency to develop this condition appears to run in families.
A few people develop astigmatism after an eye injury or surgery. A condition called keratoconus, which causes progressive thinning and bending of the cornea, eventually leads to severe astigmatism.
Contrary to popular belief, astigmatism isn’t caused or aggravated by reading in the dark or sitting too close to the TV.
The most common symptom of astigmatism is blurred vision, which occurs at both near and far distances. The blurring can be vertical, horizontal, diagonal, or any combination of these. In some cases, objects also look distorted (too tall, short, wide, or narrow). People with astigmatism often report difficult driving at night.
Squinting due to untreated astigmatism can lead to eyestrain, which in turn causes discomfort and headaches.
People with very mild astigmatism often don’t notice any symptoms.
If you notice any changes in your vision that interfere with your activities, see an ophthalmologist (eye doctor) for a comprehensive exam. Depending on your needs, this may include:
Most cases of astigmatism respond to the following treatments:
In almost all cases, astigmatism responds to treatment and won’t keep you from your daily activities. Because your eyes change over time, you may need to update your corrective lens prescription periodically to keep your vision sharp.
There is no known prevention for astigmatism. However, regular preventative care can detect the problem early and keep your corrective lens prescription up-to-date.
Healthy adults should have eye exams: