PRI Vision Training Glasses—More Than Just Prisms



Dr. Heidi Wise – PRI Vision

(This post originally appeared on the PRI Vision website at and is reposted with permission)

I get asked rather frequently by people if what we do in PRI Vision is to treat patients is to prescribe prism glasses.  This question has come in from patients, other optometrists, therapists, and I’m sure I’m forgetting others.  The answer is “sometimes”.

What is a prism?  A prism is theoretically any optical lens, regardless of whether there is power in it for making you see more clearly or not.  A prism creates an illusion, by displacing light so that the location of where an object viewed through it appears is not the same as the actual location (see picture below).  Prismatic effect generally occurs in one plane, such as left/right, forward/back, or up/down.  Only certain combinations of prisms, used with both eyes open, effect more than one plane at a time.  These generally are used in cases of eye alignment/coordination problems.

In glasses that are prescribed for seeing more clearly, prismatic effect increases the further away from the center of the lens you look.  Generally, a prescription pair of glasses will have the center of the lens lined up with your pupil to minimize how much prismatic effect you experience when you wear them. Prescription lenses also have refractive power, which means they change the size, location, as well as the clarity of the image when viewed through them.  If you have ever looked at someone with glasses on and have thought that their glasses either make their face look smaller than it is, or make their eyes look really magnified, you have seen an example of the refractive effect of lenses to magnify and minify objects when you look through them (see pictures below).


Top left: Example of image displacement by a prism (left lens)

Top right: Example of minification by lenses for nearsightedness

Bottom Left: Example of magnification by lenses for high farsightedness

My background in behavioral optometry and neuro-optometric rehabilitation provides a strong history of utilizing prisms.   I have used them for eye alignment difficulties, visual field loss, distortions in processing of visual space common after acquired brain injuries, and neglect syndromes, just to name a few.  Early on I began to feel that if prisms were going to be used, an active therapeutic intervention needed to also be undertaken in most cases so that the prisms weren’t just a “band-aid”, whose effect might seem to “wear off” with time.  This is called adaptation.

When Ron and I first started working back and forth between his office and mine, we exclusively used prisms to change patients’ position, which would result in PRI-defined neutrality.  Ron had spent a lot of time with other neuro-minded optometrists and knew the powerful effects prisms could have.  But what we noticed is that many of our patients would experience adaptation, lose neutrality, and ultimately not maintain the changes we saw initially.

Once we started working in the same room together, we began using lenses with refractive power in them, which as you see in the pictures above magnify or minify images.  This also means they expand or compress space.   We capitalize on this to alter the way our patients sense and interpret the space around them in all three planes.  This allows us to achieve more than just neutrality, by increasing the brain’s ability to control the body in a tri-planar manner.  (If you aren’t familiar with the concept of neutrality and its impact on how the entire body functions including the central nervous system, visit for more info.)   The patient then uses active, integrated therapeutic activities to get their brain and body to sense things differently, so they can learn how to move more appropriately.  As learning takes place, the need for these training lenses is reduced and the ultimate goal is elimination.

“This allows us to achieve more than just neutrality, by increasing the brain’s ability to control the body in a tri-planar manner.”

So when do we use prisms for PRI Vision?  When we can’t get enough effect in a certain plane of movement with refractive lenses alone, I will add prisms to achieve the desired result.  There are many reasons why this may be needed, which are too numerous to list here, but we use objective testing and subjective feedback to determine when it’s appropriate and when it’s not.

The power of prisms is undeniable.  PRI Vision capitalizes on the power of lenses, with an added effect from prisms when needed, in a tri-planar manner. This is what makes PRI Vision different from other modalities of postural treatment.

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