What’s the Deal with Prism Lenses?

Editor: Dr. Russel Lazarus, Published November 24, 2020

Author: Dr. Randy Schulman

EyeCare Associates, CT

Has your eye doctor prescribed prism glasses or lenses?

More recently, people are hearing more and more about prism glasses for a variety of vision problems. Prism glasses are typically prescribed for people who are experiencing double vision, as these lenses help to merge the two images into one clear image.

Why do I need prism lenses?

The following list includes the most common symptoms of vision conditions that may be alleviated with prism lenses:

  • Double vision
  • Headaches
  • Eye strain and fatigue
  • Neck, shoulder and back pain
  • Dizziness, vertigo and lightheadedness
  • Unsteady gait
  • Postural problems
  • Feeling anxious in crowds and big open spaces
  • Difficulty reading, fatiguing, losing place, words running together, etc.
  • Difficulty focusing and maintaining concentration
  • Difficulty driving for long periods

What are the benefits of prism glasses?

Prisms can be used as a therapeutic tool to provide the following benefits:

  • Alleviate diplopia (double vision)
  • Reduce stress
  • Increase comfort
  • Increase sustaining ability on near tasks
  • Increase efficiency
  • Restore postural adaptation
  • Provide control and protection against additional adverse adaptation

Prisms for the treatment of double vision 

Prisms may also be prescribed for the treatment of vision problems associated with:

Since double vision can be a sign of a serious health condition, it is important to see your doctor as soon as possible to determine the cause.

How do prism glasses work?

In normal vision, the two eyes work in tandem by pointing at the same image, simultaneously. Each eye collects distinct visual information to be sent to the brain for processing. The brain then combines the visual input from each eye to produce a single image for you to see clearly.

Double vision occurs when the two eyes are not aligned properly and are unable to work together to point in the same direction, at the same time.  As a result, the brain is unable to accurately process the distinct visual input from the two eyes to form a clear, single image.

Prisms work by moving the image to correct alignment for one eye or both eyes.  

For example, if one eye is turned outward, a base-in prism may be used to move the image to accommodate for the position of that eye. If one eye is higher or sees an image higher than the other eye, a base-down prism may be used to accommodate for that eye and move the image up.

Very often, eye doctors will prescribe more than one pair of prism glasses if varying prism powers are required for different activities. This is usually necessary if the two eyes are only misaligned intermittently or for certain distances, or when the eye turn occurs as a result of increased visual demand or fatigue.

What else do prism glasses do?

Not only do prisms displace images to improve vision, they also facilitate changes in perception, as the base of the prism slows down the rate at which light enters the eye, causing objects to appear further away.

As a result, prisms can facilitate improved depth perception, posture, gait, and movement patterns. 

Moreover, since prisms change the way light enters the eye and brain, they can have far reaching effects on the entire nervous system— affecting breathing, heart rate, muscle tonicity, and even attitude.

Do I still need vision therapy?

While prism lenses will help to relieve your visual symptoms while wearing your  glasses, vision therapy is a long term solution for your vision problems.

Vision therapy is an effective treatment for many different vision problems, including double vision.

Vision therapy retrains your eye-brain connections to improve your visual skills for clearer, single vision, with or without your eyeglasses.