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Like nearsightedness or farsightedness, astigmatism is a common condition that can typically be corrected.
If you’re like many people in the U.S., you may require some type of vision correction.
That’s because a whopping half of Americans age 20 and older have what’s called a refractive error, a type of vision problem that makes it hard to see correctly, according to a study published in the journal JAMA Ophthalmology. Common refractive errors include trouble seeing in the distance (nearsightedness) or up close (farsightedness).
One type of refractive error that can go unnoticed is astigmatism. That’s a variation. have astigmatism, according to the JAMA Ophthalmology study.
Generally speaking, “astigmatism is very benign,” says Mark Ventocilla, O.D., an optometrist with America’s Best Contacts & Eyeglasses in Muskegon, Michigan. Even better, it’s easily corrected with eyeglasses or contact lenses — if it even needs correcting.
Here’s what else you should know about astigmatism.
What is astigmatism?
Astigmatism (pronounced: uh-stig-ma-tis-em) is a common variation in the curvature of either the eye’s cornea (the front surface of the eye) or the lens inside the eye. There are two types:
- Corneal astigmatism, in which the cornea is distorted
- Lenticular astigmatism, in which the lens is distorted
Normally, the eye’s cornea or lens is “shaped with a single curve, like a basketball,” says Dr. Ventocilla. “But with astigmatism, it’s shaped with two curves, like a football.”
When the cornea and lens are smooth and round, light rays are sharply focused onto the back of the eye (the retina), allowing people to see clearly, according to the American Academy of Ophthalmology (AAO). If the cornea or lens is curved like a football, the light is improperly reflected to the back of the eye, causing blurry vision.
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What are the symptoms of astigmatism?
Some of the most common symptoms include:
- Blurry vision, or needing to squint to see clearly
- Difficulty seeing at night
Keep in mind that some of these symptoms can also be caused by other eye conditions.
People with mild astigmatism may not be bothered by any blurry vision they have — if they notice it at all. But those with more pronounced astigmatism might have more difficulty seeing.
Reading, for instance, can be hard. “If you have a lot of astigmatism and you try to read, the letters have some blur or distortion to them,” Dr. Ventocilla explains. As a result, you can get headaches from straining your eyes or struggle to remember what you’ve just read. “You’re struggling more to focus, which means it’s harder to retain what you’re reading,” he says.
People who have astigmatism can also have other vision problems, including nearsightedness (myopia) or farsightedness (hyperopia).
What causes astigmatism?
Experts aren’t exactly sure. Many people are born with it, and there’s some evidence that the condition is inherited, according to the AAO. Other people develop astigmatism later in life, as a teenager or an adult.
In some cases, astigmatism can develop from keratoconus. This is a condition in which the cornea gradually thins and bulges outward, forming a cone shape. Astigmatism also can happen after developing an eye disease, suffering an eye injury or undergoing procedures such as cataract surgery or cornea transplant surgery.
Astigmatism is not caused — or even worsened — by reading in low light or sitting too closely to the TV. That’s a common myth.
Can astigmatism be prevented?
Because astigmatism stems from a problem with the eye’s anatomy — one that is sometimes present from birth — there’s no real way to prevent it.
How is astigmatism diagnosed?
An optometrist can determine if you have astigmatism during a comprehensive eye exam. [link to Eye Exam HUB] The eye doctor will perform a series of assessments to check your vision, your prescription Some of those assessments include:
Visual acuity test. This part of the eye exam uses an eye chart — think: the classic “E” that appears on a screen — to gauge how well you can see from certain distances. You’ll read a series of letters while covering one eye, followed by the other.
Corneal topography. This special type of photography maps the surface of the cornea. (The test produces an image of the eye in much the same way researchers take a 3D map of the world, according to the AAO.)
With a topography scan, eye doctors can detect variations
Refraction. Eye doctors can use an instrument called a phoropter, which places a series of lenses in front of your eyes to measure how they help you focus light. (This device looks like an overly large pair of eyeglasses.) Your doctor will use the results to determine which type of lenses can give you the clearest vision, and how to shape the lens to correct your vision.
Even if you have no vision complaints, it’s a good idea to see an optometrist regularly for a complete eye exam. How often depends on a few different factors: Leading eye organizations, such as the AAO, recommend that people get a complete eye exam at the age of 40. That’s when early signs of eye disease tend to appear.
Others should schedule routine eye exams at a younger age. This includes people who have diabetes, high blood pressure, and a family history of eye disease. People who already wear glasses or contact lenses should see their eye doctor every year, as should those ages 65 and older.
Children should also have at least one eye exam before they enter school, and again every year they’re in school. During a comprehensive exam, an eye doctor can further evaluate them for astigmatism, among other eye problems. (Learn more about the difference between school vision screenings and comprehensive eye exams here.)
Children may not notice the symptoms of astigmatism if they were born with it, says Dr. Ventocilla. And with severe cases in kids, “astigmatism can lead to permanently reduced vision if it’s not treated early,” he says.
For example, a baby who has astigmatism may see a skewed vision of the world around them, which wires their brain a certain way, Dr. Ventocilla explains. “You can try to fix their vision with eyeglasses,” he says, “but you can’t rewire the brain, so you can still get reduced vision.”
How is astigmatism measured?
Eye doctors measure astigmatism in diopters. A perfect eye, one that doesn’t have astigmatism, has 0 diopters, according to the AAO. Most people with astigmatism measure between 0.5 and 0.75 diopters. People who have astigmatism of 1.5 or more typically need eyeglasses or contact lenses to correct for it.
The more the shape of your eye looks like a football — as opposed to a circular-shaped basketball — the more pronounced your astigmatism and the higher the number.
How is astigmatism treated?
Astigmatism isn’t an eye disease, so it can’t be “cured.” Still, there are ways to correct for it — and most people with astigmatism will see better when it’s corrected, rather than ignored, says Dr. Ventocilla. Options include:
Eyeglasses. Glasses can contain special cylindrical lenses that can compensate for the irregularity in the eye. They can also correct other types of refractive errors, which makes them a good choice for people who have astigmatism and nearsightedness or farsightedness, for example.
Soft contact lenses. These contact lenses, which are worn directly on the eyes, can allow some people to see even more clearly than they would with eyeglasses.
Some soft contact lenses are specifically designed to correct astigmatism, and these can be particularly good for people with a more pronounced condition. (One note: They tend to be more expensive than regular contacts.)
Even regular soft contacts can help correct mild astigmatism, says Dr. Ventocilla. Remember, he explains, astigmatism is an irregularity in the smooth surface of the eye. A contact lens, however, is a regular, smooth surface. “Contacts can hide or mask small amounts of astigmatism — say, less than 1/2 diopter,” he says.
One thing to keep in mind with soft contacts, sleeping in your lenses or swimming in them, for example, can increase the risk of an eye infection.
Hard contact lenses. Most people who wear contacts wear soft lenses, but some people with astigmatism choose hard contacts, even though they can be less comfortable.
The most common type of hard contact lens is a rigid gas-permeable (RPG) lens, which is made of plastic and retains a firm shape, according to the AAO.
People who have what’s called irregular astigmatism may need to opt for hard lenses. This can be the case for people who’ve undergone a cornea transplant — in which the cornea is replaced with tissue from a donor — and may have different “ridges or valleys” on certain parts of the eye where the sutures are, Dr. Ventocilla says, which causes irregular astigmatism.
Soft contact lenses, which conform to the shape of the eye more than hard lenses, can’t correct irregular astigmatism, he says. But hard lenses, in which the eye sits behind a rigid, hard shape, can better compensate for the condition.
Did you know that contact lens prescriptions need to be renewed every year? Now’s the time to book your eye exam.
Eye surgery. Certain eye surgeries can reshape the cornea, which can correct astigmatism. These surgeries include:
- LASIK (laser in situ keratomileusis). During this procedure, a surgeon makes a thin, hinged flap in the cornea, then uses a laser to sculpt the shape of the cornea before closing the flap.
- LASEK (laser-assisted subepithelial keratectomy). A surgeon will loosen the thin protective layer of the cornea called the epithelium. Then they will use a laser to change the shape of the cornea before repositioning the epithelium.
- PRK (photorefractive keratectomy). In this procedure, the surgeon removes the epithelium altogether and uses a laser to reshape the cornea. When the epithelium grows back naturally, it will fit the cornea’s new shape.
As with any type of surgery, complications can occur, including dry eye and infection, according to the Mayo Clinic. Talk to your doctor about which possible treatment may be best for you.