Astigmatism

Overview

By Sarah Maurer

If you catch yourself squinting at the television, driving slowly at night, or wondering why your image looks distorted in the mirror, astigmatism may be the culprit.

Astigmatism is a common eye condition that causes blurred vision at distances close and far. It happens when the cornea (clear front surface of the eye) or lens (a clear structure inside the eye) has an unusual shape.

Like a camera, your eye must focus all of the light rays that enter your eye from different directions down to a single point in order to create a clear picture. Normally, this happens as light passes through the curved surfaces of the cornea and lens. When these surfaces are evenly curved (like the surface of a ball), they refract (bend) the light rays and focus them on the retina, a light-sensing organ at the back of the eye. (The retina then converts the light patterns into electrical signals, which are sent to the brain via the optic nerve and interpreted as the "picture" we see.)

In reality, almost no one has a perfectly shaped cornea or lens. Steep or flat spots bend light in irregular ways, causing images to focus in front of and behind the retina. This is called a refractive error, and the result is blurry or distorted vision.

Astigmatism sometimes happens alongside other refractive errors, including:

  • Nearsightedness: Light focuses in front of the retina, causing distant objects to blur.
  • Farsightedness: Light focuses behind the back of the eye, making nearer objects blur.

Astigmatism can cause eyestrain, leading to headaches and eye discomfort. Children with astigmatism often don't realize their vision is abnormal, which can cause them difficulties with school and sports.

Causes

In most cases, the exact cause of astigmatism is unknown. The tendency to develop this condition appears to run in families.

A few people develop astigmatism after an eye injury or surgery. A condition called keratoconus, which causes progressive thinning and bending of the cornea, eventually leads to severe astigmatism.

Contrary to popular belief, astigmatism isn't caused or aggravated by reading in the dark or sitting too close to the TV.

Symptoms

The most common symptom of astigmatism is blurred vision, which occurs at both near and far distances. The blurring can be vertical, horizontal, diagonal, or any combination of these. In some cases, objects also look distorted (too tall, short, wide, or narrow). People with astigmatism often report difficult driving at night.

Squinting due to untreated astigmatism can lead to eyestrain, which in turn causes discomfort and headaches.

People with very mild astigmatism often don't notice any symptoms.

Diagnosis and Treatment

If you notice any changes in your vision that interfere with your activities, see an ophthalmologist (eye doctor) for a comprehensive exam. Depending on your needs, this may include:

  • Visual acuity testing: You'll be asked to read letters of various sizes off an eye chart from a distance of 20 feet.
  • Keratometry: The ophthalmologist uses reflected light from a device called a keratoscope to measure the curvature of the cornea.
  • Computerized corneal mapping: This involves running a keratoscope with a video camera over the cornea's entire surface to create a detailed picture of its shape.
  • Refraction testing: The ophthalmologist places a series of lenses with different shapes in front of your eyes to determine which provides the clearest vision.

Most cases of astigmatism respond to the following treatments:

  • Glasses. This is the simplest and most common option. Glasses for astigmatism contain a specialized toric (cylindrical) lens that provides additional light-bending power along a certain visual axis.
  • Contacts. These corrective lenses sit directly on the cornea surface, providing a wider field of vision. Mild to moderate astigmatism can usually be corrected with soft toric lenses. More severe cases may require rigid gas permeable lenses. Your ophthalmologist can help you determine which type is best for you.
  • Orthokeratology. This treatment uses specialized rigid contact lenses to gradually correct the curvature of the cornea. At the start of treatment, the lenses are worn for a few hours at a time (usually at night), and then removed. As the shape of the cornea improves, they can be worn less frequently. Orthokeratology is not a permanent fix; if you stop wearing the lenses, your vision issues will return.
  • Laser surgery. Several types of surgical procedures can reshape the cornea surface and provide permanent correction of some types of astigmatism.

In almost all cases, astigmatism responds to treatment and won't keep you from your daily activities. Because your eyes change over time, you may need to update your corrective lens prescription periodically to keep your vision sharp.

Prevention

There is no known prevention for astigmatism. However, regular preventative care can detect the problem early and keep your corrective lens prescription up-to-date.

Healthy adults should have eye exams:

  • Every 2-4 years between ages 40 and 55
  • Every 1-3 years from 55-65
  • Every 1-2 years after 65
  • More frequently if recommended by your physician.

Sources

  • Astigmatism. American Optometric Association. Retrieved May 21, 2015 from http://www.aoa.org/patients-and-public/eye-and-vision-problems/glossary-of-eye-and-vision-conditions/astigmatism.
  • Astigmatism. University of Michigan Kellogg Eye Center. Retrieved May 21, 2015 from http://www.kellogg.umich.edu/patientcare/conditions/astigmatism.html.
  • Diseases and Conditions: Astigmatism (Jan. 2014). Mayo Foundation for Medical Education and Research. Retrieved May 21, 2015 from http://www.mayoclinic.org/diseases-conditions/astigmatism/basics/definition/con-20022003.
  • Facts About Astigmatism (2010). National Eye Institute. Retrieved May 21, 2015 from https://www.nei.nih.gov/health/errors/astigmatism.
  • What Is Astigmatism? (2013). American Academy of Ophthalmology. Retrieved May 21, 2015 from http://www.geteyesmart.org/eyesmart/diseases/astigmatism/.