Prism is a special type of lens that shifts space and changes the way our eyes work, rather than just changing eyesight.

Here is just a sample of its uses:

1. to improve the stability of how both eyes work together
   • crucial for reading and learning
2. to re-orient posture and movement
   • potentially for torticolis and autism
3. to help visual attention
   • may be useful for ADHD
4. to compensate for field loss after brain injury
   • may be helpful for homonymous hemianopia

The need for prism in a prescription is best determined by a specially trained Doctor of Optometry. The specialized tests involved are not typically conducted as part of a basic eye examination. One of the key tests we utilize is called fixation disparity, originally developed in England, and another is the influence of prism on depth perception.

Any reputable source of eyewear can work with a laboratory that makes prism. Prism is obtained by either change the relationship of the center of a lens to the center of the eye, or by a specialized process that creates differential thinning.

In higher amounts you can see that one edge of a prism is thicker than the opposite edge. This is only true in higher powers, as needed when patients see double, or during vision therapy. Otherwise it doesn’t noticeably change the appearance of the lens.

Yes. It is possible to incorporate prism power into any prescription, including bifocal lens prescriptions.

That depends on whether the prism is working as a support or as a therapeutic tool. The average length of time is between one and two years. When it is prescribed for double vision, the length of time may be longer.

Absolutely! In one sense, prism is like medication: Just because a little bit is good doesn’t mean more is better. The amount has to be carefully determined, and is as much an art based on the experience of the doctor as it is a science rooted in optics. Patients are typically monitored at one month, three month, or six month intervals depending on the case.

That depends on why the prism is being prescribed. When used for learning purposes we anticipate improved attention, concentration and fluency. When used for convergence problems we expect less eye strain or doubling. When used for developmental purposes we anticipate improved responses to other therapies.

Prism is very individualized. Sometimes changes occur rapidly, but in other cases not for months. When prism has a beneficial effect initially, and then levels off, that may be a sign that the amount, the balance between the two eyes, or the direction of prism needs to be changed. It may also signal that the prism has done its job and should be removed.

Prism is not a panacea, but when it is indicated it can bring about remarkable changes. Dr. Press collaborates with occupational therapists, physical therapists, speech-language pathologists, reading specialists, and educators, and is very interested in feedback from them as well as parents regarding what changes are being seen.

Dr. Press published his approach to prescribing prism in a peer-reviewed journal, Optometric Clinical Practice, in 2020. It is an open-source journal so that all doctors can access and review his work.