What are Prism Lenses?

Double vision (diplopia) causes you to see two separate images of a single object. This can get in the way of everyday activities and can be especially dangerous for those who need good eyesight for their work.

Fortunately, prism glasses can help realign your vision. Here's what you need to know about prism lenses and whether they're right for you.

How Do Prism Lenses Work?

Prism glasses use specialized lenses that redirect incoming light, compensating for eye misalignment. Each prism lens is wedge-shaped, thicker at one side (the base) and thinner at the opposite side (the apex). 

When light passes through the prism, it's bent toward the thicker edge, repositioning the visual image onto the correct part of each retina. Prism strength is measured in prism diopters (Δ). 

One prism diopter shifts an image by about one centimeter at a distance of one meter. For mild double vision, you might only need a few prism diopters. Larger misalignments typically require stronger prisms.

What are the Different Types of Prism Lenses?

Prisms come in two primary types, each with distinct advantages:

• Ground-in prisms. These permanent lenses are precisely crafted for clarity, durability, and stability for long-term prescriptions. Typically used for prescriptions up to about 10Δ per lens.
• Fresnel press-on prisms. Thin, removable sheets that adhere to existing lenses. These are good for temporary conditions, rapid adjustments, or higher prism powers (up to 40Δ). May reduce visual clarity due to their textured surface.

Who Needs Prism Glasses?

Your eye doctor (optometrist) may prescribe prism glasses if you struggle with double vision alongside other eye problems, such as:

• Eye strain
• Frequent headaches
• Strabismus
• Tiredness with close-up work, such as looking at a computer

Conditions That Benefit From Prism Correction

Not all types of double vision respond equally well to prisms, but certain binocular diplopia conditions significantly benefit from prisms:

• Cranial nerve palsies. Nerve palsies due to diabetes or hypertension often resolve partially or fully over a few months. During this time, prism glasses provide effective interim relief.
• Decompensated phorias. Latent misalignments caused by age or fatigue can often be treated with prism lenses.
• Thyroid eye disease. The inflammation from thyroid eye disease can cause vertical diplopia. Prisms are often used to treat these cases.
• Stroke or traumatic brain injury. Following a stroke or traumatic brain injury, people may experience double vision. Prism glasses are essential in treating this during recovery.

When Should You See a Doctor?

Though prisms help many cases, some symptoms indicate medical emergencies requiring immediate attention:

• Sudden double vision with severe headache
• Diplopia accompanied by eye pain or pupil changes
• Double vision paired with facial numbness or weakness

If you experience these symptoms, seek urgent medical evaluation.

What Are the Potential Side Effects of Prism Lenses?

Although prism glasses are effective for correcting double vision, some people may experience the following side effects:

• Headaches
• Eye strain or discomfort
• Nausea
• Dizziness

In most cases, these can be corrected with an adjustment to the lens prescription, a change in eyeglass frames, or medication.

If you experience problems with new glasses or your old prism glasses stop working, contact your vision healthcare specialist to discuss the issue.

How Much Do Prism Lenses Cost?

The cost of prism lenses depends on the frames and whether your lenses are designed only to treat double vision. Most Fresnel prism glasses cost about $250 to $500.

Meanwhile, ground prism glasses cost about $600 to $1,500. Speak to your doctor about how much prism glasses cost and how to reduce the out-of-pocket expenses.

Here’s a breakdown of the cost:

Item	Average price
Add-on prism correction (per lens)	$100 – $300+
Complete prescription glasses with prism lenses	$200 – $600+
High-index or progressive prism lenses	$400 – $1,000+

If your prism lenses are prescribed for conditions like strabismus or double vision (diplopia), some vision or health insurance plans may partially or fully cover them. Check with your provider to see if your plan covers prism lenses.

Find an Eye Doctor for Personalized Care

Visit VisionCenter.org's "Find an Eye Doctor" tool or consult professional resources from the American Academy of Ophthalmology (AAO) or American Optometric Association (AOA) to locate a specialist near you.