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What is astigmatism?

Astigmatism is a vision problem that is defined as an error in refraction. When light strikes the eye, it is refracted, or bent, by the eye lens and the cornea, which is the transparent membrane in front of the eyeball. Errors of refraction occur if the lens, cornea, and length of the eyeball are not perfectly balanced, resulting in blurry vision.

What causes astigmatism?

Astigmatism is the result of irregularities in the cornea. Because of these irregularities, some of the light rays that enter the eye do not focus directly on the retina.

The rod cells that perceive light and the cone cells that perceive both light and color are located in the retina. These cells convert light into electrical impulses that are carried to the brain. The brain interprets these impulses, creating each person's view of the world. Someone with astigmatism sees less sharply because light rays are improperly focused on the retina.

How is astigmatism diagnosed and treated?

Refractive errors, including astigmatism, are identified during standard eye examinations and can be corrected with lenses. Different types of lenses are used for different eye problems, but all work on the same principle of properly focusing light rays directly on the retina. Cylindrical lenses, which may be made as conventional eyeglasses or contact lenses, are used to correct astigmatism. Contact lenses, however, may be contraindicated for persons with diabetes or other health problems, including various eye disorders that are unrelated to astigmatism.

What can I do myself?
A person cannot correct any refractive error without glasses or contact lenses prescribed by an eye-care professional. Contrary to popular belief, eye

exercises and special diets are of no benefit in curing astigmatism.

When should I see my doctor?
Everyone should have regular eye examinations starting early in childhood. Even if a person has no vision problems, the eyes should be checked periodically. A person who is otherwise healthy should have an eye examination every 3 years up to the age of 35, and every year or 18 months thereafter. More frequent examinations are recommended for people with diabetes, high blood pressure, or other conditions that may affect the health of the eyes.

A person should see an eye doctor right away if he or she experiences any changes in vision or pain, burning, or a feeling that something is lodged in the eye. Ophthalmologists (medical doctors who are specialists in eye diseases) and optometrists (graduates of schools of optometry) are both qualified to examine eyes and prescribe corrective lenses if an error of refraction is diagnosed.

Opticians specialize in filling the ophthalmologist's or optometrist's prescription for eyeglasses or contact lenses, but they are not medically qualified to examine the eyes.

What will the doctor do?
The doctor will obtain a medical history with special attention to any vision problems and how they have been treated in the

A chart made up of parallel black bars is used to determine the axis of astigmatism.

past. Various tests will be performed as part of a physical examination of the eyes. An instrument called an

ophthalmoscope and another device known as a slit-lamp microscope are used to check for injuries, eye disease, and various problems that can result in impaired vision.

Reading an eye chart is the initial test involved in diagnosing astigmatism and other errors of refraction. If a person is unable to read this chart, the doctor will have the patient look through an instrument called a phoropter as different types of lenses are inserted. The phoropter pinpoints the correction needed to bring the vision as close as possible to 20/20 — a measurement that indicates what a person with normal vision sees at a distance of 20 feet. This standard is used for prescribing corrective lenses.

If a person needs corrective lenses, the doctor will help the person decide whether to choose glasses or contact lenses. Some eye doctors have an optician on the premises who can grind the lenses as prescribed and fit them into the frames. If not, the doctor will give the patient a prescription to take to an optician.

The course of astigmatism

Astigmatism rarely worsens with age, but changes in vision caused by other eye problems, such as near- or farsightedness, may make it seem more noticeable. It can be readily corrected with the proper lenses.

Is astigmatism dangerous?
It is not a threat to health, but a severe astigmatism can interfere with vision enough to making driving or operating power tools dangerous. Anyone who has had corrective lenses prescribed should wear them as directed, especially when driving or performing tasks that demand clear vision.