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
“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.
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.
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.
Prognosis of Astigmatism
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.
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.
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.
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.
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 causes decreased vision in one or both eyes.
Research and Statistics: How Many People Have Astigmatism?
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.
Conditions Related to Astigmatism
Astigmatism can sometimes occur with both myopia and hyperopia.
Resources We Love
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.
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.
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.