When you see an eye doctor about blurred vision, they'll probably give you an eye exam to assess your eye's ability to focus on near and far objects. Your eye doctor may also check for astigmatism, another condition that can affect your vision. Find out what happens during an astigmatism test.
What is Astigmatism?
Astigmatism is an eye condition that causes blurred or distorted vision for both near and far vision. Your eye is normally shaped like an oval, but when astigmatism occurs, your cornea has an irregular curve, leading to blurred vision. Astigmatism is a lifelong condition and typically appears at birth, according to the American Optometric Association.
Astigmatism may cause the following symptoms:
- Blurry vision
- Distorted vision, especially in severe cases
Regular eye exams are important in identifying changes in patients with astigmatism.
“If a patient has trouble seeing with their eyeglasses or contacts on, it could be that astigmatism is not being corrected,” William Wiley, MD, medical director of the Cleveland Eye Clinic, tells WebMD Connect to Care.
How Do Eye Doctors Test For Astigmatism?
There are several methods of astigmatism testing. None of them are invasive.
Eye Exam with Vision Test
According to the American Optometric Association, a complete eye exam includes a vision test and is one way to test for astigmatism. Your doctor can determine how well you see a chart with letters or symbols. Your doctor may also switch between lenses using a phoropter, an instrument that helps determine the best corrective lenses for your vision. Eye doctors can determine the strength of your prescription using these vision tests.
A retinoscope is a handheld instrument that projects a beam of light into your eye, according to the American Association for Pediatric Ophthalmology and Strabismus. During a retinoscopy, your doctor moves the beam vertically and horizontally to observe the movement of the reflected light. A retinoscopy can be done quickly and is especially helpful when testing young children for astigmatism.
According to the American Optometric Association, astigmatism can be diagnosed by taking your corneal topography during a test called photokeratoscopy. It’s a technique that maps the curve of your cornea using a special camera.
“We can then see changes of a thinning cornea or if astigmatism is progressing in order to determine if there is corneal disease,” Sonny Goel, MD, founder and CEO of Goel Vision, tells WebMD Connect to Care.
The Duochrome Test
Goel says the duochrome test, or the “red and green” test, is used to refine your prescription and not necessarily to determine astigmatism. It’s a subjective exam during which you state whether letters are clearer on the red or green section of the test.
“If vision is sharper when reading on the red side, vision is undercorrected, and if vision is sharper on the green side, there is too much correction,” Goel says. “The goal is to be evenly balanced.”
Astigmatism Tests Online
At-home tests can help determine whether you may have astigmatism. One example of an astigmatism test pattern is a diagram that resembles the spokes of a wagon wheel with the same width and boldness. If you see some spokes darker than others, you may have astigmatism.
These tests shouldn’t be a replacement for an eye exam at your doctor’s office.
“Doctors spend a lot of time refining the way to measure and correct astigmatism,” Wiley says. “An in-office exam gives a patient access to expertise that cannot be duplicated with online self-testing.”
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