Seeing double? If so, you may be a candidate for prism glasses, a type of eyeglasses that can correct for double vision (also known as diplopia).  

Unlike other types of eyeglasses, which typically correct for myopia or hyperopia, prism glasses help align two images and merge them into one, according to the American Academy of Ophthalmology (AAO). 

“The prismatic effect in the lenses can help prevent double vision, which can be a difficult thing for people to deal with,” says Whitney Wallace, O.D., an optometrist at America’s Best Contacts & Eyeglasses in Bolingbrook, Illinois. 

Here’s a guide to prism lenses, including how they work and what to know once you start wearing them. 

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What Causes Double Vision? 

In many cases, people who have double vision are born with a slight misalignment of their eye, says Dr. Wallace. For example, one eye can point slightly inward or upward from the other. 

“For most of your youth and early life, the muscles of your eye are able to subconsciously pull themselves into alignment to fuse the images from each eye, so that you see a single image,” she explains. “But sometimes, when people get older, they lose that ability to align their eyes and see one image, so they start seeing double.” 

Many people notice double vision for the first time when they’re reading a book or looking at their cell phone. The words will start to “split” in two, Dr. Wallace says.  

In other cases, though, double vision can be temporarily caused by conditions such as diabetes, a migraine, or a concussion. Oftentimes, that vision trouble will eventually subside, either on its own or with treatment. 

Double vision can also be caused by more serious health conditions, such as thyroid eye disease, cataracts, or myasthenia gravis (an autoimmune disease that causes muscle weakness). 

“If someone comes in, we can do some extra testing to figure out if this is something that can be treated with prism glasses,” says Dr. Wallace. That’s one reason why you should see a doctor right away if you start experiencing double vision, especially if it’s appearing for the first time. “The patient should go for further testing to rule out bigger health concerns rather than immediately treating them with prism glasses,” she says. 

How Do Prism Glasses Work? 

Under normal circumstances, we see an object through both eyes because the light from that object falls on the same part of our eyes’ retinas (the back part of the eye), according to the AAO. When you have double vision though, the light falls on different parts of each retina. 

Prism eyeglasses shift the light before it reaches the eye, which allows your brain to see one single image instead of two. For example, if your eye points downward instead of straight ahead, your eye doctor will place the prism at the top of your lens, she says. 

 
“When you look through the lenses, it reduces the burden on the eyes to pull themselves into alignment,” says Dr. Wallace. 

Prism lenses can also be combined with your regular prescription, she says. For example, someone with myopia can have prism eyeglasses that correct their double vision while also helping them see into the distance. 

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Will Anyone Notice I’m Wearing Prism Lenses? 

Prism eyeglasses look the same as any other pair of eyeglasses, so no one will be able to tell you’re wearing a different type of lens, says Dr. Wallace. 

“There’s no impact on how the glasses look,” she says. 

Can I Have Prism Lenses in My Contacts? 

Probably not. Eye doctors are only able to put a tiny amount of prism into a contact lens, which likely wouldn’t be able to fix your misalignment. “Only a minority of people would need such a small amount,” says Dr. Wallace. “People who need prism lenses unfortunately aren’t good candidates for wearing contacts.” 

Tips for First-Time Wearers 

Usually, once you need prism glasses, most likely you’ll need them for life, says Dr. Wallace. Here’s how to make the adjustment. 

Ask your optometrist if you can try them out first. Some patients may be able to try a temporary Fresnel prism. This is a thin, vinyl sticker that can be fitted onto your existing eyeglasses, which allows you to see how prism lenses work, according to the AAO. 

A Fresnel prism can also be used if your prescription isn’t stable yet — for example, if you have myasthenia gravis, and your condition is still progressing. Unlike with prism lenses in your eyeglasses, the lines on a Fresnel prism are slightly visible. 

Give it time. It may take a few days to adjust to your new glasses, just as it would with any other change in your prescription. “There’s a normal adaptation period,” says Dr. Wallace. 

During this time, you might experience a little bit of eyestrain, according to the AAO. 

Call your doctor if you aren’t getting any relief. Rarely, people who wear prism glasses can experience more double vision, headache, nausea, and eye pain. If that happens, call your doctor right away. Prism glasses “should relieve trouble,” Dr. Wallace says. 

“Usually, people get into a prism lens and what I’ve seen is that they’re very happy and comfortable,” says Dr. Wallace. “They adapt well to that initial prescription, and that is what works really well for them for years or decades.” 

Medically reviewed by Whitney Wallace, O.D. 

See our sources: 
Prism correction in eyeglasses: American Academy of Ophthalmology 
Diplopia (double vision) overview: Cleveland Clinic 
How diabetes affects the eyes: American Academy of Ophthalmology