Astigmatism is a common vision problem caused by an error in the shape of the cornea. With astigmatism, the front surface of the eye (the cornea) or the lens of the eye has an irregular curve, which can change the way light is passed to the retina (or refracted). This causes blurry, fuzzy, or distorted vision. Farsightedness and nearsightedness (hyperopia and myopia) are two other types of refractive errors.
It is not known what causes astigmatism, but genetics is a big factor. It is often present at birth, but may develop later in life. It may also occur as a result of an injury to the eye or after eye surgery. Astigmatism is often accompanied by nearsightedness or farsightedness.
The two main types of astigmatism are:
A corneal astigmatism is when the cornea is misshapen.
A lenticular astigmatism is when the lens is misshapen.
Astigmatism can occur in children and adults. Your risk of developing astigmatism may be higher if you have any of the following:
- a family history of astigmatism or other eye disorders, such as keratoconus (a degeneration of the cornea)
- scarring or thinning of the cornea
- excessive nearsightedness (blurry vision at a distance) or farsightedness (blurry close-up vision)
- a history of certain types of eye surgery, such as cataract surgery (surgical removal of a clouded lens)
- your risk of developing astigmatism may be increased if your mother smoked when she was pregnant with you, according to a study published in the October 2011 issue of Ophthalmology
The symptoms of astigmatism may differ in each person. Some people do not experience any symptoms at all. Symptoms of astigmatism include:
- blurry, distorted, or fuzzy vision at all distances (close-up and far away)
- difficulty seeing at night
- eye irritation
See a doctor if you experience symptoms of astigmatism. Some symptoms may also be caused by other health or vision problems.
Astigmatism is diagnosed by an optometrist (a licensed healthcare professional who diagnoses vision problems and eye diseases), or an ophthalmologist (a medical eye doctor who provides medical and surgical treatment of vision problems and eye diseases), through a comprehensive eye examination. Tests optometrists and ophthalmologists may use during your eye examination to diagnose astigmatism include:
Visual Acuity Assessment Test (VAT)
During a VAT, your optometrist or ophthalmologist will have you read letters from a chart at a specific distance to determine how well you can see the letters.
A refractor test is performed using a machine called an optical refractor. The machine has multiple corrective glass lenses (like eyeglass lenses) of different strengths. Your optometrist or ophthalmologist will ask you to read a chart while looking through different strength lenses on the optical refractor, until he finds a lens that appropriately corrects your vision.
During a keratometry examination, your optometrist or ophthalmologist will look at your eye through a keratoscope machine to detect and measure the curvature of your cornea.
Mild cases of astigmatism may not require treatment. Astigmatism that causes vision problems may be treated by an optometrist or ophthalmologist using one of the following methods:
Corrective eyeglasses and contact lenses prescribed by an optometrist or ophthalmologist are the most common and least invasive treatment for astigmatism.
Ortho-K is a treatment that uses rigid contact lenses to temporarily correct the irregular curvature of the cornea. The rigid contact lenses are worm for limited periods of time, such as during sleep, and removed during the day. Some people are able to achieve clear vision during the day without corrective lenses when undergoing Ortho-K. The benefits of Ortho-K disappear when it is discontinued, and vision usually returns to what it was before treatment.
For severe cases of astigmatism, your doctor may recommend refractive surgery. This type of surgery uses lasers or small knives to reshape the cornea to permanently correct astigmatism. The three common surgeries for astigmatism are laser in situ keratomileusis (LASIK), photorefractive keratectomy (PRK), and radial keratotomy (RK). All surgeries carry some risks. Talk to your doctor about the risks and benefits before getting surgery for astigmatism.
Vision can usually be restored to normal with corrective lenses, or after corrective surgery. There is no known way to prevent astigmatism from developing.
If a person only has astigmatism in one eye, and does not correct it, amblyopia (a lazy eye) may develop.
Written by: Rose Kivi and Elizabeth Boskey, PhD
Medically reviewed by George Krucik, MD