What Is Astigmatism? Symptoms, Causes, Diagnosis, Treatment, and Prevention

Astigmatism is when the front surface of your eye, called the cornea or lens, has imperfect curvature rather than being round.

Astigmatism, nearsightedness (myopia), farsightedness (hyperopia), and loss of near vision with age (presbyopia) are the main types of refractive errors, which is when the shape of the eye doesn’t bend light correctly and results in blurred vision or visual impairment.

In many cases, astigmatism doesn’t significantly impact sight and doesn’t need to be treated. People with more pronounced astigmatism can have their vision corrected with glasses, contact lenses, or surgery.

Signs and Symptoms of Astigmatism

Many people who have mild astigmatism may not even realize it. People who have more severe astigmatism can have symptoms that include blurred vision, eye discomfort, squinting, and headaches.

“One indication you have astigmatism is if you’re in a dark room and you look at the little red or green LED light on a television or modem, and instead of looking perfectly round, it looks sort of stretched out. That’s because of some astigmatism in your eye,” says Craig See, MD, an ophthalmologist at Cleveland Clinic in Ohio.

Astigmatism Causes and Risk Factors

“Astigmatism is usually caused by the shape of the cornea,” says Dr. See. The cornea is the clear part on the front of your eye, the place where a contact lens would rest on your eye, he explains. Many people are born with astigmatism, but it's unknown why, he adds.

“The cornea acts as a lens. It bends light to focus it on the back part of the eye. Astigmatism is an optical change in which light coming in one direction is bent differently from light coming in from the other direction,” says See.

The shape of the cornea is very important; if the cornea’s shape is not perfect, your vision isn’t going to be perfect, he says.

“What normally causes astigmatism is if the cornea is steeper in one direction than it is in the other direction,” he says. Imagine your cornea is like a sphere, similar to a beach ball — that would be an eye with no astigmatism. With astigmatism, the cornea is shaped more like an American football.

The imperfect shape of the sphere causes things to be blurry — images are not focused properly, says See. “An astigmatism is one factor that can affect your vision; there’s lots of components that can, but that’s one of them,” he says.

Certain factors may increase a person’s chances of having astigmatism, including a family history of astigmatism, eye disease, or keratoconus.

Keratoconus is a degeneration of the cornea in which the cornea thins in the lower and center parts.

“This is a fairly common condition that typically starts when somebody is in their teens, and it usually continues to get worse until about age 40, although in some people it can get worse past age 40,” says See.

One main risk factor for keratoconus is rubbing your eyes, he explains. “The mechanical injury from repeatedly rubbing your eye can sort of stretch out the cornea and cause it to lose its strength,” he says.

Allergies and sleep apnea increase the risk of keratoconus, says See. “It’s also common in people with Down syndrome because of increased rubbing of the eyes,” he says.

Some other things that raise the chance of astigmatism include:

Some types of eye surgery, such as cataract removal
A history of corneal scarring or thinning
A history of severe nearsightedness or farsightedness
A mother who smoked during pregnancy

How Is Astigmatism Diagnosed?

An ophthalmologist can diagnose astigmatism by looking at the shape of the cornea and how your eyes bend light with instruments that are designed to do that, or by checking your vision, says See.

Tests for astigmatism include the following:

Visual acuity This test involves reading letters of different sizes on a distance chart. There are alternative methods for children or nonverbal people.
Keratometry or topography Both of these tools can measure the curvature of the cornea to measure the astigmatism.
Refraction This is the part of the eye exam where you look through a special device called a refractor or phoropter and the eye doctor asks, “Which is better, one or two?” and then flips between different lenses.

The astigmatism measurement is one part of an eyeglasses prescription, says See. The “sphere” (SPH) on the prescription is the lens power needed to correct your vision. The “cylinder” (CYL) number is how much astigmatism you have, and the “axis” is where the astigmatism is on the cornea.

Prognosis of Astigmatism

Astigmatism doesn’t cause disease or any other medical condition.

Laser surgery can correct some types of astigmatism; an eye exam is necessary to determine who is a candidate for this type of corrective surgery.

Although wearing prescription eyeglasses or contact lenses won’t improve astigmatism, they can help people see clearly.

Duration of Astigmatism

A small amount of vertical astigmatism (where the vertical curve is not perfectly shaped) may improve or even go away because of the constant pressure on the lids. More pronounced horizontal astigmatism may gradually get worse; it can be corrected with contacts or eyeglasses or treated with surgery, but it won’t go away on its own.

Treatment Options for Astigmatism

There are a few ways to correct astigmatism, including prescription eyeglasses and contact lenses, says See. “Many times people with astigmatism do better with contact lenses, because if you put a strong astigmatism-correcting lens in front of an eye, it can tend to stretch things out and cause distortion; if that lens is closer to the eye, like in a contact lens, you tend to get less distortion,” he says.

“Depending on the type and severity of your astigmatism, there are different surgical options to correct it,” says See.

Laser-assisted in situ keratomileusis (LASIK) It is possible to treat astigmatism with LASIK surgery, says See. In LASIK surgery, the surgeon makes a thin, hinged flap in your cornea, and tissue is removed from the inner layer to sculpt the shape.

“You want to be sure there isn’t some form of keratoconus (thinned cornea) going on before surgery; if you do LASIK surgery on someone with keratoconus, you can actually make their vision worse,” he says.

Laser-assisted subepithelial keratectomy (LASEK) In this procedure, the above surgery is performed but the cornea is accessed by loosening the epithelium (the protective cover of the cornea) with a special alcohol rather than cutting the cornea and creating a flap.

Photorefractive keratectomy (PRK) This surgery is used to correct astigmatism, and it can be an option if your doctor thinks you’re not a good candidate for LASIK. In PRK, the surgery is similar to LASEK but rather than loosening the epithelium, the surgeon removes it.

Lens surgery This procedure is performed on the lens inside the eye to treat astigmatism, including in people with astigmatism caused by keratoconus, says See. The uneven curve is corrected by replacing the eye’s natural lens with an intraocular lens (IOL), called a toric lens.

“This surgery is commonly done when we do someone’s cataract surgery,” See says. When a person has a cataract, the eye’s lens is cloudy, which causes things to look blurry or less colorful. Lens removal and replacement with a clear IOL improves vision.

Intacs surgery This surgery is an option for some people with keratoconus that worsens to the point where glasses or contact lenses no longer provide clear vision. Two small plastic crescents (called Intacs) are placed within the cornea to make the corneal surface more regular, which can improve vision, although glasses or contact lenses are sometimes still needed.

Small-incision lenticule extraction (SMILE) This surgery reshapes the cornea by using a laser to create a lens-shaped piece of tissue below the cornea surface, which is then removed through a very small incision.

Corneal cross-linking This light-activated treatment can strengthen and stabilize the cornea, which can be very effective in preventing someone’s keratoconus from worsening, says See. In the procedure, riboflavin (vitamin B2) drops are placed in the eyes, then a type of ultraviolet light is shone on the cornea, causing new corneal collagen cross-links to form.

Risk of Complications in Astigmatism Surgery

As with any type of surgery, there is a risk of complications as a result of surgery for astigmatism.

“One of the most serious complications of LASIK surgery can be if you cause the person’s cornea to lose its strength, which can happen as a result of making cuts and removing some of the tissue. Vision can get progressively worse, and a person might need contact lenses or even a cornea transplant to see if this happens,” See says.

There can also be over- or undercorrection of the astigmatism, says See. “For example, if the goal is to treat 100 percent of it, but you only end up treating 80 percent of it. In an overcorrection, the person could end up with astigmatism in the other direction,” he says. In either case, person might still need glasses or contacts to see clearly, he adds.

Other potential complications of surgery to correct astigmatism include visual side effects such as a starburst or halo appearing around lights, infection, dry eye, and corneal scarring.

Alternative and Complementary Therapies

“There aren’t any alternative or complementary therapies that can cure astigmatism,” says See.

There are eye “exercises” — movements that include things like blinking, rolling, or focusing your eyes in a specific way, but these methods haven’t been proven to improve vision or astigmatism.

Prevention of Astigmatism

If you have astigmatism, it may be worth it to ask your doctor if you have keratoconus, says See. “If you have keratoconus there are treatments that could help prevent it from getting worse, especially if you catch it early,” he says.

Complications of Astigmatism

Astigmatism can worsen and get to the point where glasses no longer correct the vision, in which case the person may need to wear a special hard contact lens, says See. “We have lots of patients who are totally dependent on their hard contact lenses; without these, they don’t see well enough to drive or read,” he says.

If a person is unable to wear contacts or they get a scar on their cornea, they might need a corneal transplant, says See.

Amblyopia, or “lazy eye,” can occur in children who have uncorrected astigmatism in only one eye.

Amblyopia causes decreased vision in one or both eyes.

Research and Statistics: How Many People Have Astigmatism?

Approximately one in three people have some degree of astigmatism, and it often happens in conjunction with nearsightedness or farsightedness.

BIPOC Americans and Astigmatism

Research has shown disparities in the incidence of astigmatism in members of Black, Indigenous, and People of Color (BIPOC) communities when compared with white populations. Black children, Hispanic children, and Asian children are all at an increased risk of astigmatism compared with non-Hispanic white children.

A study that included 4,040 participants published in Optometry and Vision Science found that 17 percent of all children had astigmatism, 17.4 percent of African American children, 22.2 percent of Hispanic children, 18.2 percent of Asian children, and 11.4 percent of white children. Native American children had the lowest risk, at 7.9 percent.

Black, Hispanic, and Asian Americans often have less access to comprehensive eye care; cultural and language barriers can keep many people from getting the needed diagnosis and treatment.

Conditions Related to Astigmatism

Astigmatism can sometimes occur with both myopia and hyperopia.

Myopia (nearsightedness) In myopia, you can see objects close to you clearly, but distant objects are out of focus and blurry; this can lead to headaches and eyestrain. It’s caused by the shape of the eye: In a person who is nearsighted, the light coming into the eye bends incorrectly, focusing images in front of the retina rather than on the retina.

Hyperopia (farsightedness) Hyperopia occurs when the eye is shorter than normal or the cornea is too flat, causing the light rays to focus beyond the retina rather than on it. Typically, people who are farsighted can see distant objects relatively clearly, but nearby objects are blurry and out of focus.

Resources We Love

American Academy of Ophthalmology

This professional association of eye doctors and surgeons has as their mission to protect sight and empower lives through patient advocacy, education, and advancing the profession of ophthalmology. The association provides information for patients about astigmatism as well as other eye conditions and diseases on EyeSmart.

EyeCare America

This program of the American Academy of Ophthalmology offers free eye exams for eligible people over the age of 65 or who are at risk of glaucoma.

National Eye Institute (NEI)

The NEI was first established by Congress to protect and prolong the vision of the American people. The NEI supports eye disease research through grants and training. They also offer information about eye health for adults and children.