What are prism glasses?

When you focus on an object, your eyes should create one image. However, some people see two images instead. This is known as diplopia, also called double vision. Prism glasses can help correct misalignments that trigger diplopia, so your brain stops bombarding you with extra images. You may also need prisms if you have convergence insufficiency or another type of binocular vision dysfunction.

Understanding prism glasses  

Prism glasses can be a game changer for people who struggle with binocular vision dysfunction and similar conditions. You may need prescription prism glasses even if you have 20/20 vision. In fact, you may still be able to pass a standard eye exam with binocular vision problems. Many patients do not initially realize dizziness, anxiety, or derealization come from a visual misalignment. Good thing we're here to give you the rundown, right?

What are prism glasses? 

Prism glasses bend light before it hits your eyes. This helps redirect light to the correct part of your retina, which then converts images into messages for your brain. Simply put, your retina tells your brain, "Hey, this is an apple," by sending info via the optic nerve. When you wear prism lenses, it can make it easier for each retina to receive and transmit the correct images.

Applications of prism glasses 

Buy-one-get-one-free sales are fun at the grocery store, but a two-for-one deal can be stressful when it involves your vision. When light sneaks into your eye at the wrong angle, it can cause double vision. You may see two of everything all the time or only in certain situations, like when you are trying to read or perform close-up tasks. 

Prism lenses help eliminate double vision and blurred or distorted vision caused by structural misalignments. Binocular vision dysfunction, also called BVD, is one condition that may benefit from prism lenses. When you have BVD, your vision may get blurry at times, even when regular eye exams are fine. This happens because each eye is busy doing its own thing, and the brain gets confused by the conflicting images.   

Prism correction and binocular vision

Binocular vision issues can cause headaches, dizziness, anxiety attacks, motion sickness, and other unpleasant symptoms - and who wants that? Your brain panics when light enters the retinas at different angles, so it tries to get your attention with these symptoms. Prism glasses help fix this issue by telling your brain everything is aligned correctly. Prism lenses change the direction of light, so the rays hit each retina at the same angle. When this happens, your brain relaxes because it sees matching images rather than conflicting ones. 

Binocular vision disorders 

Your eyes are supposed to work as a team. When they don't, you may experience binocular vision disorders, such as strabismus and convergence insufficiency. Strabismus, also called hypertropia, occurs when your eyes cross and face two different directions instead of looking straight ahead together. This may mean that one eye drifts toward your nose or your temple. 

Convergence insufficiency describes eyes that don't work well together when doing close-up tasks, such as reading or sewing. You may notice eye strain, blurred vision, or double vision if you have convergence issues. 

These issues may occur if you have weak or overly tight eye muscles, but they can also be caused by subtle misalignments. One eye might sit slightly higher than the other, or you may have damage to your facial nerves or muscles. This can happen after a stroke or head injury. 

Sometimes, your brain can overcompensate for the misalignment, but eventually, it becomes too tired to fight your vision issues. When this happens, you may benefit from prism glasses. Prism lenses help give your brain and eyes a break so your body no longer has to fight to see clearly. 

Role of prism correction

As we mentioned earlier, prism glasses change the way light enters your retina. Your eye muscles no longer have to strain to filter light correctly because the prism lenses take over that job. When light enters each retina at the same angle, you can achieve proper binocular fusion. In other words, your eyes work better as a team instead of fighting each other. This helps correct issues such as blurred or double vision because your brain thinks your eyes are aligned. 

Types of prism glasses

There are several different types of prism glasses for binocular vision disorders. You can get prism lenses made of glass or plastic and choose from an assortment of frames. 

Horizontal prism glasses 

Horizontal prisms describe prisms that help correct horizontal misalignment. You may see this adjustment written as BI (base in) or BO (base out - not body odor) on your eyeglass prescriptions. These numbers show where the prisms are placed in your prescription glasses. You may benefit from horizontal prism lenses if your eyes drift toward your nose or the side of your face, creating a visual misalignment. 

Vertical prism glasses 

Vertical prisms help address a vertical misalignment. Rather than seeing matching BI/BO numbers on your prescription, you may notice different BU (base up) or BD (base down) measurements. Vertical prisms can be helpful for patients with vertical heterophoria. This means you have a misalignment vertically, rather than horizontally. Your eyes may drift upward or downward instead of to the sides. 

Prism glasses are often prescribed when patients need prisms. However, some patients can get mild vertical prisms in their contact lenses. 

Yoked prism glasses

Yoked prisms can help correct binocular vision problems in patients with gaze palsies, where the nerves or muscles do not move correctly in the eyes. This can happen after a stroke or neck injury. Yoked prisms help enhance visual coordination by making the brain think that the eyes are moving in the same direction instead of working against each other. 

Prism glasses: Key takeaways 

If you have normal binocular vision, congrats! It means that your eyes work well together. Binocular vision dysfunction occurs when your eyes each choose their own adventure. This can leave you with headaches, dizziness, eye pain, and even debilitating anxiety.

Fortunately, you can encourage your eyes to be team players by trying prescription prism glasses. Prism lenses change how light enters your retinas, which tells your brain that everything is okay with your vision. Instead of double vision or blurred images, you should see one crisp, clear image. 

If you suspect you have a vision misalignment, consult an eye care professional for solutions. You may find that you need prism lenses, contacts, or other vision tools to manage your condition. 

FAQs

Are prism glasses suitable for children? 

Prescription prism glasses can be worn by adults or children. However, many providers also have children try a vision therapy program for binocular vision dysfunction. 

Can prism glasses be worn all day? 

Some people only wear prisms for reading, driving, or using a computer. Your vision care provider will let you know if your prism glasses should be worn all day.

How do I find the right eye care professional for prism glasses? 

Ask your eye care professional if they have experience treating diplopia, convergence insufficiency, binocular vision dysfunction, or similar conditions. These providers can often prescribe prism glasses for vision correction.