How do online astigmatism tests work?
Medically reviewed by Johnson & Johnson Principal Research Optometrist, Ben Straker, BAppSc(Optom)
Think about it: There aren’t very many tests that you can take online about things relating to your health. There’s no online test to detect the flu, or to tell what you’re allergic to, or to check for suspicious moles. And for good reason. Since medical conditions can look different for different people, they require the assessment and diagnosis of a trained and licensed health care professional. And while astigmatism is no different—an official diagnosis requires a comprehensive eye exam—the nature of astigmatism allows us to provide a simple and quick online test that can tell whether or not you might have astigmatism. You’ll notice the “might” in there. The test is effective for many people, but it’s not perfect. Read on, and we’ll dive into what astigmatism is, and how the online astigmatism test works.
The science of astigmatism, simplified
Astigmatism can be a tricky eye issue to explain, and simplifying it requires glossing over some of the specifics. Keep in mind, if you have any further questions about astigmatism, it’s best to reach out to your eye doctor.
How a typical eye works
The front of your eye is home to your cornea and crystalline lens. For most people, the curve of both is uniformly round, like a sphere. The round shape means that no matter where light enters the eye from, it’s passing through the same curve shape. This helps the light focus consistently in one spot in the eye.
How an astigmatic eye works
With astigmatism, your cornea or lens isn’t spherical, it’s shaped more like an American football. That means there isn’t just one curve shape for light to pass through—there are two, each with its own “steepness,” or degree of curvature. Because of this, when a person with astigmatism looks at an object, the light from that object is directed to two different focal points in the eye at the same time. For example, one point could be on the retina and one could be behind the retina. Having two focal points creates blurry or distorted vision.
What to know to understand online astigmatism tests
One focal point is closer to the retina
So far, we’ve learned that with astigmatism, the two different curves of the eye focus incoming light on two different places. This simple fact is the basis for the astigmatism test. Two focal points in the eye means that one focal point will be closer to the retina and therefore more in focus. How does this apply to the astigmatism test? Depending on your astigmatism, a line in one direction (the one oriented with the curve that focuses light closer to the retina) would be clearer and bolder than the rest of the lines.
The orientation of your astigmatism is unique to you
You may have figured out by now that the test takes advantage of the orientation of the two curves of an astigmatic eye. Those two curves are always at a 90º angle with respect to each other (keep the image of a football in mind), but the tilt is unique to the person. This is why a contact lens prescription for astigmatism includes a number referred to as the AXIS. This is describing the “tilt” of your astigmatism.
Let’s tie it all back to the astigmatism test
Now, if a person with astigmatism on a 30º axis were to take the test, the line they’d likely see clearest would be at 30º or 120º (two curves oriented 90º from one another) depending on which of their two curves has a focal point closest to the retina. The rest of the lines would not be as clear or crisp because they’d either fall on the focal point furthest away from the retina, or somewhere in between.
Do your glasses have astigmatism correction?
Our online astigmatism test also can help you figure out if your eyeglasses already have power to correct astigmatism. When a cross-hair is viewed through each lens as the lens is rotated, the image will “scissor” if the lens includes a correction for astigmatism. It works similarly to the speedometer test. The lenses have two curves, each with an orientation that complements the astigmatism it corrects.
Frequently asked questions
Important Information for Contact Lens Wearers: ACUVUE Contact Lenses are available by prescription only for vision correction. An eye care professional will determine whether contact lenses are right for you. Although rare, serious eye problems can develop while wearing contact lenses. To help avoid these problems, follow the wear and replacement schedule and the lens care instructions provided by your eye doctor. Do not wear contact lenses if you have an eye infection, or experience eye discomfort, excessive tearing, vision changes, redness or other eye problems. If one of these conditions occurs, remove the lens and contact your eye doctor immediately. For more information on proper wear, care and safety, talk to your eye care professional, call 1-800-843-2020, or download the Patient Instruction Guides.
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