Patient guide
Astigmatism: what it is, and the ways to correct it
Astigmatism changes gradually. Call (609) 246-0236 the same day for sudden blurred or lost vision, a shadow or curtain across your vision, new flashes or floaters, eye pain, or a red eye that is sensitive to light.
Astigmatism is not a disease. It is a question of shape: the front of the eye is curved more steeply in one direction than the other. About one American adult in three has enough of it to matter, and glasses and contact lenses correct it.
This page explains what it is, what the numbers on your prescription mean, the ways to correct it, and the two situations where it deserves a closer look: in a young child, and when it keeps increasing.
What it is
An eye without astigmatism is curved evenly, like a ball. With astigmatism, the cornea, the clear front of the eye, is shaped more like the back of a spoon: steeper one way than the other. Light then focuses at two places instead of one, so things blur at every distance.
Evenly curved. The cornea bends light the same amount in every direction, and a point of light lands as a point.
Astigmatism. One direction is curved more steeply than the other, so the two focus at different depths and the point is drawn out into a smear.
The uneven curve can be in the cornea or in the lens inside the eye. A small amount is normal and very common, and it often comes along with nearsightedness or farsightedness.
In ordinary astigmatism the surface is smooth, and glasses correct it. When the surface itself is uneven, as in keratoconus or after a scar, it is called irregular astigmatism, and glasses may not bring vision up to where it should be.
What it looks like
- Blur at every distance. Far and near are both affected.
- Smeared or shadowed letters.
- Streaky lights at night, and more trouble seeing at night generally.
- Squinting, tired eyes and headaches.
- Nothing at all. With mild astigmatism you may not notice any symptoms.
None of these is special to astigmatism. An eye exam is the only way to find out whether you have it, and how much.
Where it comes from
- It runs in families. Why the shape of the cornea varies from person to person is not known, but the tendency is inherited.
- It usually starts early. Some people are born with it, and many develop it as children or young adults.
- It can follow an eye injury, eye surgery or eye disease.
- It can change. Astigmatism can shift gradually as the eye grows or ages. It may increase, decrease or stay the same.
- Nothing you did caused it. Reading in low light or sitting close to the television does not cause astigmatism or make it worse, and there is no known way to prevent it.
In a national survey of American adults, 36 percent had astigmatism of 1.00 diopter or more in at least one eye. It was more common in people aged 60 and over than in younger adults.
How it is measured
- Refraction. The part of the exam where lenses are compared in front of each eye. It finds the amount of astigmatism and its direction.
- Keratometry. A measurement of the curve of the cornea.
- Corneal topography. A detailed map of the shape of the cornea, which shows whether the surface is smooth or uneven. It needs no drops, and nothing touches the eye, and it is taken in this office when the shape of the cornea is in question.
On your prescription
Two of the numbers on a glasses prescription describe astigmatism.
- Cylinder (CYL)
- The extra power that corrects astigmatism. Blank or zero means little or none. The farther from zero, the more astigmatism.
- Axis
- The direction of the astigmatism correction, from 1 to 180 degrees. It is a direction, not a strength, so a bigger number is not worse.
A prescription written −2.00 −1.25 × 180 means −2.00 of nearsightedness, 1.25 of astigmatism, and a correction lined up at 180 degrees.
The national survey above counted a cylinder of 1.00 or more as enough to matter. How to read the rest of your prescription.
Correcting it
- Glasses. The most common correction. A new astigmatism correction, or a change in one, can take up to a week to get used to. Floors may look tilted and edges curved at first. Wear the new glasses full time; switching back and forth to the old pair resets the clock.
- Soft toric contact lenses. Contact lenses made for astigmatism, in daily and reusable forms. They are weighted to stay in the right orientation on the eye. Fitting them is routine here.
- Rigid and scleral lenses. Rigid gas permeable lenses give the sharpest vision and correct irregular corneas by letting the tears fill the gap underneath. Scleral lenses are larger rigid lenses that vault over the cornea on a layer of fluid. The kinds of contact lenses.
- Laser surgery. LASIK and related procedures reshape the cornea so that it focuses light correctly. Whether it suits you depends on your prescription, corneal shape and tear film, all measured here. The procedure is performed by an ophthalmic surgeon; the assessment before and the follow-up after are done in this office.
- At cataract surgery. A toric lens implant corrects astigmatism as well as the cataract, reducing the need for distance glasses. Cataracts and choosing the lens.
- Nothing. Mild astigmatism may not need correcting at all.
Astigmatism in children
Children may not realize that their vision is blurred, because they assume everyone sees that way. In a young child, a large amount of astigmatism, or a big difference between the two eyes, can keep an eye from developing full sharpness even with glasses later. That is lazy eye (amblyopia), and it is best caught early.
A child with astigmatism can pass a school screening. What a children's eye exam checks.
When it keeps changing
Early keratoconus, a thinning and bulging of the cornea, can look like ordinary astigmatism. These are the signs that something more is going on:
- A glasses prescription that keeps changing, especially more astigmatism each year
- Vision that is not fully sharp even with new glasses
- Ghost images or doubling in one eye, lines that look bent or wavy
- Soft contact lenses that no longer give clear vision
Frequent, hard eye rubbing is one of the strongest links to keratoconus found in studies, and the one you can change. If any of these fit, a map of the cornea settles the question.
Common questions
Is astigmatism an eye disease?
No. It is a focusing problem, like nearsightedness and farsightedness, and it comes from the shape of the eye. An eye with astigmatism is usually a healthy eye.
Will it get worse?
It can change gradually as the eye grows or ages, and it may increase, decrease or stay the same. Regular exams track it. Astigmatism that goes up year after year is worth a closer look at the shape of the cornea.
Did screens or reading in poor light cause it?
No. Reading in low light or sitting close to a screen does not cause astigmatism or make it worse.
Can I wear contact lenses if I have astigmatism?
Yes. Toric lenses for astigmatism are routine, in daily and reusable forms, and rigid or scleral lenses cover the corneas that soft lenses cannot. What a fitting involves.
Why do my new glasses make the floor look tilted?
A new or changed astigmatism correction changes the shape of what the brain receives, and the brain takes up to a week to recalibrate. Wear the new pair full time. If it has not settled after two weeks, call, because a lens that was made or fitted wrong is fixable.
Do drugstore reading glasses work if I have astigmatism?
They suit many people when both eyes need about the same power and there is little astigmatism. They do not correct astigmatism, so with more of it, prescription lenses will be sharper. Reading glasses and the other options after forty.
Can eye exercises fix it?
No. Exercises cannot change the curve of the cornea.
Does this go through my vision plan or my medical insurance?
A routine exam for glasses or contact lenses usually goes through a vision plan. If you are coming in about a symptom or a condition, it is a medical visit and goes through your medical insurance. Vision plan or medical insurance explains the difference.
Book an eye exam
A routine exam checks your prescription and the health of each eye at the same visit.
Book an exam Call (609) 246-0236
Khoury Eye Care, Hamilton Mall, 4403 Black Horse Pike, Mays Landing.
Sources
The figures and recommendations on this page come from the following. Ask at your visit if you would like a copy of any of them.
- National Eye Institute. Astigmatism. Updated December 2024.
- American Academy of Ophthalmology. Astigmatism explained: causes, diagnosis, treatment.
- Vitale S, Ellwein L, Cotch MF, Ferris FL 3rd, Sperduto R. Prevalence of refractive error in the United States, 1999-2004. Archives of Ophthalmology. 2008;126(8):1111-1119.