You’ve likely heard this expression before, or some variation thereof: “If your only tool is a hammer, everything starts to look like a nail”. I’ve mentioned this in the context of prism glasses being used as a substitute for vision therapy. Most of us don’t see the “easy asthenopia cases” any more. We’re seeing ABI, ASD, SRD – complex problems requiring many tools in a vast shed. For these populations VT requires a significant commitment in time and resources on the part of the doctor and staff. It would be much simpler to take an alternate route and prescribe prism glasses of some sort for every patient who walks through the door. Let’s look at some of the implications of this approach.
So if we can lend that analogy to this problem, let’s call it the PEZ (Prism EZ) Factor. There are guidelines that have been suggested for prescribing prism in a classical sense for so-called decompensated hetereophoria, and some have suggested that the concept of prism adpatation is overrated and therefore clinicians should be more aggressive in Rxing prism. The debate about whether or not “prism is poison” dates back to at least 1920, the year my father was born, and he’s getting old. Over the past 30 years the discussion has slowly extended to yoked prisms.
Perhaps we can agree on this: prism is neither a poison nor a panacea. Therefore it should always be considered, but not prescribed in wholesale fashion. And by that I mean that it would be as illogical to claim that every patient with a visual performance issue needs a prism Rx as it would be that every orthopedic problem could be solved with a shoe lift to redistribute weight bearing, or that every auditory processing problem could be solved with a hearing aid of some sort.
The irony to me, and it bears repeating, is that the goal of optometric vision therapy is to provide the patient with sufficient learning opportunities so that they can become effective indpendent learners. If we believe that vision is a form of intelligence, and that the flexibility of one’s adaptability is a meaure of intelligence, the idea of trying to substitute a prism Rx for vision therapy is at the very least counter-intuitive.
The PEZ dispensing of yoked and micro-prisms merits some drum banging. Don’t get me wrong: when they work, prisms are a marvelous first line intervention. The cost is relatively minimal compared to office-based VT, and there is virtually no commitment in terms of time – a commodity as precious as currency these days. The downside is that when prisms have no demonstrable effect, or only fleeting effects but are Rxed anyway, parents or other professionals may conclude that other forms of visual intervention are not likely to succeed.