Many people have heard the word astigmatism in passing or may even know that they have it, but they may not be clear on the details. This common eye condition affects roughly one-third of the population, and around 70% of all eyeglass and contact prescriptions include an astigmatism correction.

What is Astigmatism?

Astigmatism is a common refractive error within the eye. In people with the error, the cornea has an egg-like shape rather than a mostly circular one. This causes light to focus unevenly on the retina, the light-sensitive tissue in the back of the eye that sends messages to the brain. Because the brain is interpreting these messages into the images that the eye sees, the images have flaws.

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What are the Symptoms?

People with astigmatism can experience various symptoms. In many cases, astigmatism is present at birth but causes no issues initially. Often, optometrists will mention the condition without prescribing a treatment or altering a prescription. When the symptoms do appear, the most common are blurry or distorted vision [at]. Eyestrain, discomfort, and headaches may occur if a person does not receive corrective treatment. He may notice himself squinting in an attempt to see more clearly and his night vision may be worse than average. It is common for astigmatism to occur alongside other vision issues (like myopia), causing many people to confuse the condition's symptoms.

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What Causes Astigmatism?

Doctors know that astigmatism results from a cornea with an irregular shape, but nobody is sure of the cause. Astigmatism affects the meridians in the cornea. To understand meridians, think of the eye as the face of a clock. A meridian is a line that connects three and nine or two and eight. Principal meridians are the steepest and flattest. A person with astigmatism has one meridian with a larger curve than the meridian perpendicular to it. Because the condition is often present at birth, researchers believe certain people have inherited genes that affect cornea shape. However, it is also possible to develop astigmatism later in life, which points to non-genetic causes, as well, such as the result of an eye injury.

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Are There Different Kinds of Astigmatism?

There are three primary forms of astigmatism:

  • Hyperopic astigmatism means that one or both of the principal meridians are farsighted.
  • Myopic astigmatism means that one or both principal meridians are nearsighted.
  • Mixed astigmatism means one meridian is farsighted and the other is nearsighted.

Beyond these three primary forms, a variety of terms help optometrists and ophthalmologists further classify astigmatism. Corneal astigmatism is the common form of astigmatism that affects the cornea. Lenticular astigmatism occurs when the lens, rather than the cornea, has an irregular shape. Doctors may also refer to astigmatism as regular or irregular. Regular astigmatism means that the principal meridians are perpendicular to each other, while irregular means they are not.

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Who is at Risk?

Because doctors aren't aware of the underlying cause of astigmatism, it is hard to identify the characteristics of at-risk individuals. Existing evidence suggests people with the following factors could make one more likely to develop or be born with astigmatism:

  • a family history of astigmatism or eye disorders such as keratoconus
  • thinning or scarred corneas
  • excessive farsightedness or nearsightedness
  • a history of eye surgery, particularly cataract surgery

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How Do Doctors Diagnose Astigmatism?

A diagnosis for astigmatism usually begins with an eye inspection using direct light. If the doctor suspects the condition, they will conduct more comprehensive tests including a visual acuity assessment test that has the patient read letters of varying sizes from a chart. The doctor may also use an optical refractor to see if a corrective lens will improve the eyes'incorrect refraction. One of the most effective tests involves using a keratometer to measure the curvature of the cornea.

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Are There Corrective Options?

Thankfully, astigmatism responds well to minor medical interference. The most common treatment for astigmatism is a pair of corrective lenses, glasses, or contacts that help compensate for the incorrect refraction. For some people, doctors may prescribe rigid contact lenses to correct the curvature of the cornea temporarily. This treatment, orthokeratology or Ortho-K, may allow people to see normally when they are not wearing their corrective lenses as long as they continue the treatment. Advanced cases of astigmatism may require refractive surgery.

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Is Corrective Surgery Safe?

Corrective surgeries are safe as long as a qualified eye surgeon performs the procedures. However, all medical procedures carry some risks, of which all prospective patients should be aware. The various forms of LASIK, LASEK, and other laser surgeries often cause dry eyes. and in some cases may cause more severe symptoms. Glare, halos, and double vision are possible, as are under or overcorrections. Procedures such as photorefractive keratectomy involve removing the outer portion of the cornea, which usually involves moderate to severe pain after the surgery.

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Is it Possible to Have Astigmatism and Not Know?

It is quite common to have astigmatism and not be aware of it, mostly because the condition can be asymptomatic. Alternatively, if the condition is causing issues, people often assume they are slightly nearsighted or farsighted. They may also experience symptoms and never realize that the way they are seeing is not the same as everyone else. This is particularly common in children and young adults.

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When are Eye Exams Necessary for Astigmatism?

Astigmatism often changes throughout a person's life. To account for this, optometrists recommend frequent eye exams to adjust prescriptions for corrective lenses and to ensure surgery has not become necessary. The American Optometric Association recommends children get eye exams at six months, three years, before first grade, and every two years after that. Children with severe astigmatism should receive eye exams yearly. Adults should have eye exams at least every two years. People with diabetes or other eye conditions should visit an eye doctor annually.

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