What is astigmatism?
Astigmatism is one of the most common eye problems among people of all ages. It occurs when the cornea, the spherical, clear front surface of the eye that allows light to enter the eye, is abnormally curved or deformed. Normally, the cornea is round, like a basketball. But for every 1 in 3 people in the United States, the cornea is more football shaped. Astigmatism usually occurs in both eyes, although rarely are both eyes affected the same way.
Normally, light enters through the cornea and is crisply focused as it reaches the retina, which is at the back of the eye. The abnormal shape of a distorted cornea deviates those light rays so the image spreads out, reaching the retina at a different angle. The result is blurry vision. This effect can be compared to a wavy mirror, where the image is distorted.
It is possible to have astigmatism alone, but usually if someone has astigmatism, they also have other vision issues, such as nearsightedness (myopia) or farsightedness (hyperopia). Astigmatism, along with myopia and hyperopia fall into a group of eye conditions called refractive errors.
Anyone can get astigmatism at any age. It also can worsen over time. The most common sign of astigmatism is blurry vision. Someone who is also nearsighted or farsighted may not realize that the blurriness is caused by the cornea shape.
Astigmatism can be corrected by correcting vision with glasses, contact lenses, or laser surgery. There aren’t any long-term complications related to not being treated, but blurriness may get worse, making it difficult to see clearly.
What are the types of astigmatism?
There are two main types of astigmatism: corneal astigmatism and lenticular astigmatism.
With corneal astigmatism, the front surface—the cornea itself—is curved or distorted in an abnormal shape. With lenticular astigmatism, the normal curvature of the lens inside the eye takes on the football shape, rather than the basketball shape.
Astigmatism can be further divided into regular or irregular astigmatism. “Regular” means the astigmatism is consistent across the width of the cornea. Regular astigmatism is the most common type and correctable with glasses, contact lenses, or refractive surgery.
Irregular astigmatism is more difficult because the astigmatic error varies along different portions of the cornea. Irregular astigmatism can be present from birth or acquired after trauma, corneal surgery, or other corneal disorders like keratoconus. Rigid contact lenses are often prescribed to correct irregular astigmatism.
What are the symptoms of astigmatism?
Astigmatism symptoms can be easy to miss at first, particularly among children. In fact, children may not complain because they may not realize their vision is not as sharp as it should be. They may think the blurriness or distortion is normal.
Aside from blurry vision, the most common symptoms of astigmatism include:
- Eye strain
Seeking help from an eye care professional can help relieve those symptoms. This is particularly important for children who may fall behind in school if they cannot see clearly.
What causes astigmatism?
Doctors don’t know why people develop astigmatism. It can happen any time throughout life. Some babies are born with it, some people develop it well into adulthood.
Reading in low light or being too close to a television screen has been blamed for causing astigmatism. This is not true though, say eye professionals.
What are the risk factors for astigmatism?
While doctors are not sure what causes astigmatism, there are a few factors that increase the risk of developing the condition. Not all people with risk factors will get astigmatism though. Risk factors for astigmatism include:
- Eye injury
- Eye surgery
- Keratoconus, a condition where the cornea begins to thin and becomes distorted
- Other family members with astigmatism
Because doctors do not know why astigmatism occurs, it is not a condition you can prevent or stop. However, early and regular eye examinations can catch it before the blurriness affects vision.
How do doctors diagnose astigmatism?
An optometrist or ophthalmologist may suspect astigmatism based on the description of blurry vision and other symptoms, but an eye exam is needed for a diagnosis.
The doctor will likely perform:
- Visual acuity test. Patients look at a standardized chart from 20 feet away and try to identify the letters (with each eye separately) as the letters get smaller with each line.
- Keratometry/topography. This test is specific to diagnosing astigmatism. Using a device called a keratometer, the doctor looks at the curvature of the cornea to see its shape.
- Refraction test. The doctor places various lenses in front of each eye and measures how the eyes focus light from a hand-held retinoscope.
What are the treatments for astigmatism?
Astigmatism treatments concentrate on altering how the light enters the eye, removing blurriness.
- Eyeglasses, the most common treatment for astigmatism. They contain a special lens that helps compensate for the curve in the cornea or eye lens. People who are nearsighted or farsighted, or both, can have these conditions corrected at the same time.
- Contact lenses. Hard lenses or toric lenses specifically designed for treating astigmatism are fit for each individual. Usually, people with astigmatism wearing contact lenses must also have glasses to use when they cannot wear contact lenses.
- Surgery. Refractive surgery uses laser beams to reshape the cornea. There are several types, including LASIK and PRK. In extreme cases of astigmatism, an ophthalmologist may recommend transplanting the abnormal cornea with a healthy cornea or implanting a contact lens-type device inside the cornea. Irregular astigmatism caused by keratoconus may also be treated with a minimally invasive procedure called corneal cross-linking.
How does astigmatism affect quality of life?
Astigmatism does not generally affect quality of life unless the blurriness really compromises vision. Left undiagnosed, children with astigmatism may experience difficulties in school. What often happens, especially among children, is that it only becomes obvious how bad the vision was after it has been corrected. Eye care professionals recommend an eye exam at 1 year and just before kindergarten. If there is a family history of eye or vision problems, your child may need to see an eye doctor on a more regular basis.