Understanding astigmatism: Answers to common astigmatism questions
Most people have a good understanding of nearsightedness and farsightedness, but when it comes to astigmatism, things seem to get more complicated. Even though many people have some degree of astigmatism, it’s not as widely understood as other common vision problems.
This list of questions and answers about astigmatism is designed to offer all the information you need.
What is astigmatism?
Astigmatism occurs when the surface curvatures of the eye’s cornea or lens refract (or bend) light onto more than one focal point within the eye. (Illustrative video)
In most cases, astigmatism is caused by unequal curves in different meridians of the cornea. Think of meridians as lines connecting numbers on the opposite sides of a clock face. For example, a line connecting 12 and 6 is one meridian. The steepest and flattest meridians are called the principal meridians, which typically are 90 degrees apart.
Ideally, all meridians of the cornea are symmetrically curved, like a baseball. This symmetry means that light rays entering the eye from any angle will all be focused onto the same spot.
With astigmatism, the curvatures are not symmetrical. The horizontal curvature might be flatter than the vertical curvature, or vice versa. The curvatures more closely resemble the shape of an American football or an egg.
Due to this asymmetry, light rays are refracted onto multiple focal points inside the eye instead of just one. Depending on the number and locations of those focal points, vision can be blurred or distorted at multiple distances.
How common is astigmatism?
According to the American Academy of Ophthalmology, around one-third of the U.S. population, or one person out of three, has astigmatism.
What does mixed astigmatism mean?
In mixed astigmatism, the principal meridians of the cornea are significantly different in curvature, causing one meridian (the steeper one) to be nearsighted, and the other (the flatter one) to be farsighted.
Mixed astigmatism is relatively uncommon. In most eyes with astigmatism, the principal meridians are both nearsighted or both farsighted, but in different degrees.
What is irregular astigmatism?
Irregular astigmatism is a relatively rare form of astigmatism in which the principal meridians of the cornea are not 90 degrees apart from each other. In some cases, irregular astigmatism is caused by keratoconus or scarring of the cornea from an injury.
The unusual shape of irregular astigmatism makes it difficult to correct with eyeglass lenses or soft contact lenses designed for astigmatism. In many cases, however, irregular astigmatism can be corrected with rigid gas permeable contact lenses.
What makes astigmatism different from nearsightedness and farsightedness?
Astigmatism, nearsightedness (myopia) and farsightedness (hyperopia) are all types of refractive errors. Refractive errors happen when light rays can’t hit the retina properly due to the shape of the cornea, the lens or the eye in general.
With nearsightedness, the curvatures are symmetrical but are too round, or the whole eye is too long from front to back. This causes light entering the eye to be refracted to a focal point in front of the retina, rather than on the retina.
Farsightedness is the opposite — the curvatures are symmetrical but not quite round enough, or the eye is too short from front to back. Light rays that enter the eye end up at a focal point somewhere behind the retina.
With astigmatism, the curvatures are asymmetrical. They are shaped like the side of an American football rather than round like a baseball. This creates multiple focal points of light within the eye, rather than just one. Astigmatism usually occurs along with myopia or hyperopia.
SEE RELATED: Can astigmatism cause myopia?
What are the symptoms of astigmatism?
The main symptom of astigmatism is blurry or distorted vision at more than one distance. For example, you might need to squint to see the television and the computer screen. Some people may also notice that things look “wavy,” either in peripheral vision or when looking directly at something.
However, astigmatism isn’t always severe enough to noticeably affect vision. In addition, young children with astigmatism might have always had blurry vision and therefore don’t realize their vision is different than anyone else’s.
Squinting, headaches, eye strain and poor night vision can all be symptoms of uncorrected astigmatism in people who don’t have other vision problems. If you notice these issues in yourself or your child, you should schedule an eye exam to find out whether astigmatism is the problem. Even if you don’t technically “need” prescription lenses (to pass your vision test for a driver’s license, for example), wearing them could significantly reduce headaches and eye strain.
Read more about the symptoms of astigmatism.
Is astigmatism hereditary?
Some types of astigmatism probably do have a genetic component. According to the American Academy of Ophthalmology, the exact cause of astigmatism isn’t known, but it is more common among people who have a family history of the condition.
Some evidence also suggests that astigmatism is slightly more common in people of Hispanic and African American descent. There is also some evidence that smoking during pregnancy can increase the chances of the baby having astigmatism.
At what age does astigmatism usually occur?
Most people with astigmatism are born with the condition, but it might not be diagnosed until later. It can develop at any age, though, from an injury, other eye conditions, after a surgery or due to other changes in the shape of the cornea.
How is astigmatism diagnosed?
As part of a comprehensive eye exam, your eye doctor can diagnose astigmatism by measuring the curvatures of your corneas and performing tests to see how your eyes refract light onto your retinas.
How is astigmatism measured?
If you have astigmatism, the numbers on your prescription will indicate how much lens power you need to correct for the astigmatism, as well as where the power is needed.
The amount of lens power needed is measured in diopters, and the lens power to correct astigmatism is listed in the “cylinder” column. This is because the lens will only have corrective curve in one direction, like a cylinder, to balance the powers of the principal meridians of your eye. The higher the number, the more lens power is needed.
The number in the axis column is the lens meridian that won’t have corrective curve. It is perpendicular (at a 90-degree angle) to the corrective meridian. The meridians are numbered in degrees, with the horizontal and vertical meridians at 180 degrees and 90 degrees, respectively.
See a helpful graph about meridians and learn more about eyeglass lens prescriptions.
Is 20/20 vision possible with astigmatism?
Yes, people with very mild astigmatism can still experience 20/20 uncorrected vision (vision without corrective lenses). However, the letters on the “20/20” line of the eye chart won’t be as distinct as they are for someone with no refractive error.
It is also possible for people with noticeable astigmatism to achieve 20/20 vision with glasses, contact lenses and/or laser vision surgery. However, it will depend on the severity and type of astigmatism.
If the degree of astigmatism is high, corrective lenses might not be able to provide 20/20 vision. Also, some types of astigmatism may not be corrected with lenses but can be corrected with refractive surgery.
Read more about astigmatism treatments.
Can you get astigmatism if you aren’t born with it?
Yes, it is possible to develop astigmatism if you aren’t born with it, though it is much less likely.
As the eyes grow and mature, their shape can change slightly. Most people with astigmatism are born with eyes that are more egg-shaped (from the front view) than round. It is possible that their eyes can become less egg-shaped over time.
For people born with round, “normal-shaped” eyes, especially for those who have higher degrees of myopia, it’s possible the shape may become less round and more like an egg over time, which can introduce astigmatism.
Astigmatism can also develop due to other eye conditions, an eye injury or after an eye surgery.
Why is my vision still blurry with astigmatism contacts?
The two most likely reasons are that the contacts are new and your eyes are still adjusting, or they are old and your prescription has changed.
If it has been longer than three or four days since you got the contacts, you should return to your eye doctor to make sure the prescription is accurate and that the contacts are fitted properly. Likewise, if it’s been more than a year since your last eye exam, you should see your eye doctor for a comprehensive exam and to have your prescription updated.
Contact lenses for astigmatism are more difficult to fit than regular lenses. It may be a good idea to find an eye doctor whose primary focus is specialty lenses to ensure you get the best type of lens and fit for your eyes.
Can astigmatism go away?
In most cases, very young children “outgrow” astigmatism; however, the likelihood of outgrowing astigmatism decreases after ages 5 to 6.
After the age of 25, astigmatism will typically stay the same. It can also gradually worsen with age or due to other eye conditions. Fortunately, most astigmatism can be easily corrected with eyeglasses, contact lenses or laser vision surgery.
Can LASIK correct astigmatism?
LASIK and other laser refractive surgeries are usually effective options for correcting regular astigmatism. If you have mixed astigmatism or irregular astigmatism, you may still be a good candidate, depending on your lens prescription.
Be sure to find a laser surgeon who is experienced with astigmatism corrections for an in-depth consultation.
Are glasses or contact lenses better for astigmatism?
Contact lenses and eyeglasses are both safe and effective ways to correct astigmatism. LASIK, PRK and other laser refractive surgeries can also be good options.
Wearing ill-fitting or the wrong type of contacts, or wearing contacts for too long, can make astigmatism worse in some cases. If you know you have astigmatism, talk to your eye doctor to make sure you have appropriate contacts.
Can astigmatism get worse or better?
Unfortunately, astigmatism can worsen over time, and it won’t get any better after around the age of 25. The natural aging process or other eye conditions can cause the shape of the eye to gradually change, which can intensify astigmatism.
However, progressing astigmatism can usually be easily corrected with glasses or contact lenses, just like other progressing refractive errors. It may be best to wait to correct astigmatism with refractive surgery until any progression has stopped.
Contact a local eye doctor to schedule an eye exam if you think your astigmatism is getting worse. It might simply be time to update your lens prescription.
Can astigmatism cause lazy eye?
Yes, uncorrected astigmatism can cause amblyopia, also known as lazy eye. If one eye has significant astigmatism, myopia or hyperopia, the brain can start to “tune out” the visual information from that eye and only use the information from the eye with better vision.
This kind of amblyopia is called refractive amblyopia. In many cases, it can be treated by consistently wearing glasses that correct the astigmatism, along with vision therapies prescribed by your eye doctor.
Why do my astigmatism glasses make me dizzy?
People often need a period of adjustment to get used to a new lens prescription, and that includes glasses that correct astigmatism.
If you have just been diagnosed with moderate or severe astigmatism, or if you had a significant change in your astigmatism prescription, you may feel dizzy or get headaches for a few days while your eyes adjust to corrective lenses.
If it’s been more than a few days, your eyeglasses prescription may be incorrect, or your lenses might not have been made properly. Schedule another visit with your eye doctor to double check that your prescription is accurate.
At what age can children have LASIK surgery to correct astigmatism?
One of the main criteria for undergoing LASIK is that your eyes have stopped growing, which is usually not until at least age 18. Another is that your lens prescription needs to be stable, meaning unchanged, for at least one year. Astigmatism can continue to change (get better or worse) until around age 25.
Having LASIK or another refractive surgery before the eyes are done growing or before vision is stable can lead to vision regression. This is when vision is corrected for a time but then gets worse again because the original reason for the refractive error is still getting worse.
For more LASIK Q&As, visit our Ask the LASIK Surgeon page.
Are glasses always required for astigmatism?
No, not always. Some astigmatism is very mild, and sometimes astigmatism only occurs in one eye while the other eye has clear vision.
Prescription eyeglasses for astigmatism are generally considered optional if your uncorrected vision (meaning your vision without corrective lenses) is 20/40 or better. However, even if your vision is 20/40 or better, you might still end up with eye strain or headaches if you don’t wear glasses.
If it’s been more than two years since your last eye exam, you should visit your eye doctor to make sure your prescription hasn’t changed. During your exam, your doctor can show you how well you can see with glasses. Even if you don’t technically “need” them, you may be surprised how much clearer the world is with your astigmatism fully corrected.
Will astigmatism get worse if my glasses prescription is wrong?
Wearing glasses can’t make astigmatism worse, even if they are the wrong prescription. Astigmatism is caused by the shape of the eye’s cornea or lens, and glasses can’t change those.
However, wearing glasses with an incorrect astigmatism prescription can cause other problems, including blurry vision, eye strain and headaches. Depending on how “wrong” your prescription is, your corrected vision may not be legal for driving.
You should see your eye doctor at least every other year to make sure your glasses prescription is up to date. (If you wear contact lenses, you should have annual eye exams.)
Can cataract surgery cause astigmatism?
Yes, it is possible for astigmatism to be induced by cataract surgery. It’s also possible for mild astigmatism to worsen due to cataract surgery.
Cataract surgery requires an incision through the cornea. Sometimes, the way the incision heals ends up changing the cornea’s curvature. Astigmatism after cataract surgery may also be caused by the lens implant used.
Corneal healing after surgery isn’t always predictable, but a lot of the risk of astigmatism after cataract surgery can be avoided by finding an experienced cataract surgeon. If you do develop astigmatism after cataract surgery, it can often be corrected with glasses or a follow-up refractive surgery.
Click the link to learn how cataract surgery may be able to fix astigmatism.
Can wearing contact lenses cause astigmatism?
It is possible to develop contact lens-induced astigmatism. If you wear your contacts for too long or they don’t fit properly — or both — they can reduce the amount of oxygen your corneas receive.
This kind of astigmatism can usually be reversed by not wearing contacts for a while and then wearing a different type of lens afterward. It’s important not to wear contact lenses for too long. Talk to your eye doctor about how long is appropriate for you to wear your contacts; it isn’t the same for everyone or every type of lens.
Please note: If you have an urgent question about your eye health, contact your eye care practitioner immediately. This page is designed to provide general information about vision, vision care and vision correction. It is not intended to provide medical advice.
Page published on Thursday, August 13, 2020