What is Astigmatism?
Astigmatism is a type of refractive error, which means that it affects how your eye focuses light. In an eye with astigmatism, light fails to focus properly on a single point on the retina, which is necessary for clear vision. Instead light falls on multiple focal points in front of your retina, behind your retina, or both.
Astigmatism is typically caused by an irregular shaped cornea (a condition called corneal astigmatism). Instead of the cornea having a round, symmetrical shape it is shaped more like a football, where one meridian is significantly more curved (like a football), refracting the light that enters the eye in a way that distorts your vision. In some cases, astigmatism is caused by the shape of the lens itself (a condition called lenticular astigmatism).
The best way to describe meridians is to think of your eye as a clock face, with one line connecting the 12 and 6 and another connecting the 3 and 9. These two lines are called the principal meridians. Between each of your principal meridians are other meridians. Astigmatism can occur along any meridian.
There are three types of astigmatism: Myopic astigmatism, hyperopic astigmatism, and mixed astigmatism.
- Myopic astigmatism: Myopic astigmatism occurs when one or both of the principal meridians on the eye are nearsighted.
- Hyperopic astigmatism: Hyperopic astigmatism occurs when one or both of the principal meridians on the eye are farsighted.
- Mixed astigmatism: Mixed astigmatism occurs when one principal meridian is nearsighted and the other is farsighted.
Who Gets Astigmatism?
Astigmatism is incredibly common in the United States affecting approximately one in three people according to the American Academy of Ophthalmology.
You are at a higher risk of developing astigmatism if:
- You have a family history of astigmatism or other eye disorders (such as keratoconus)
- Your cornea has thinned or is scarred
- You are excessively nearsighted, which creates blurry vision at a distance
- You are excessively farsighted, which creates blurry vision up close
- You have undergone some types of eye surgery such as cataract surgery.
Your likelihood of having an astigmatism is also influenced at last partially by your ethnic group. According to a 2003 study conducted by the American Medical Association individuals of Asian or Hispanic descent are statistically more likely to have astigmatism than other ethnic groups. Of the 2523 children studied 33.6% of Asian children and 36.9% of Hispanic children had some degree of astigmatism, compared to only 20.0% of African American children and 26.4% of Caucasian children.
Symptoms & Indicators
Not everyone with astigmatism experiences the same symptoms, and some individuals don’t have any symptoms at all. However, some symptoms of astigmatism include:
- Blurry, fuzzy, or distorted vision either up close or far away
- Trouble seeing clearly at night
- Irritated eyes
If you have any of these symptoms you may have astigmatism. However, these symptoms may also be indicators of other health or vision problems, so it is important for you to see your eye care professional if you experience any of them.
What Does Astigmatism Look Like?
A Cross Section of an Eye With Astigmatism
Visual Example of How Someone With Astigmatism Sees
How is Astigmatism Treated?
Astigmatism can be treated using either corrective lenses, corrective contact lenses, or laser eye surgery.
The most common and least invasive way to treat your astigmatism is by using corrective eyeglasses or contact lenses as prescribed by your eye care professional.
Ortho-K (also known as orthokeratology, corneal molding, or corneal reshaping) is a treatment that uses rigid contact lenses to temporarily correct the irregular curvature of your cornea and may be used to treat astigmatism in some cases. Ortho-K involves wearing the rigid contacts for a limited period of time, typically overnight while you sleep, and then removing them during the day. This temporarily reshapes your cornea, allowing for clear vision. However, you can only reap the benefits of Ortho-K when you use your rigid contact lenses on an ongoing basis: Your vision will revert to its previous state over the course of the day, so you will need to wear your Ortho-K lenses every night in order to have clear vision during the day.
Laser Eye Surgery
Depending on the severity of your astigmatism your eye care professional may recommend you undergo laser eye surgery. Laser eye surgery involves using lasers to reshape your cornea, thereby permanently correcting your astigmatism. The three most common types of laser eye surgery for astigmatism are:
- Laser in situ keratomileuses (LASIK)
- Photorefractive keratectomy (PRK)
- Radial keratotomy (RK)
Like any surgery laser eye surgery carries some risks, and you should talk to your eye care professional about the risks and benefits of undergoing laser eye surgery for astigmatism before you make a decision.