In the previous blog I cited an example of a patient with no habitual Rx, in which learning toward the conservative side of prescribing is usually the way to go (“less is more”). This is part of the subtle art of prescribing, particularly when it involves prism. In this instance I’ll cite a case which, as the Binocular Vision Gods would have it, was the patient I had immediately following the preceding patient.
Joseph is 29 years old, and came in with the chief complaint of eye strain and squinting when reading, with frequent periods of double vision at near. His habitual Rx was:
OD: -8.75 -2.50 cx 005/ 1^ BU –> 20/20
OS: -9.00 -1.25 cx 180 –> 20/20
He had an habitual head tilt toward the right side. For the purposes of patient confidentiality, I’ll substitute an online photo of head tilt to the right.
Through his habitual Rx, Joseph measured 9 prism diopters of right hyperphoria in primary gaze with orthophoria horizontally, and 10 prism diopters of right hyperphoria in the reading position on downgaze, with 12 prism diopters of exophoria. Sensory testing showed intermittent alternating suppression at distance, and suppression of the right eye at near.
Based on the least amount of prism to attain fusion, and the best balance between distance and near, I trial framed 3^ BD OD and 3^ BU OS. Joseph was noticeably more comfortable with this when reading text. I added low plus at near, as well adding a low amount of base in prism, and neither trial resulted in improved clarity or comfort. I reviewed my findings with Joseph, and indicated that his “regular” optometrist was on the right track by prescribing vertical prism. It just turned out that in his case he needed a higher dosage of prism before it could have a therapeutic effect.
I added that I would see him back after he obtained the prism, and I would orient him on vision therapy activities. It was then that Joseph pulled a three dot card out of his pocket, and adding almost parenthetically that he had seen a surgical specialist before COVID started who said that he didn’t need eye muscle surgery, but could try eye exercises – which he found useless.
I explained to Joseph in plain English that the principle of the card is useful in some cases, but that his primary problem was in the vertical plane, and the card works only on horizontal problems.
Joseph left my office with an Rx of:
OD: -8.75 -2.50 cx 005/ 3^ BD
OS: -9.00 -1.25 cx 180/ 3^ BU
In my clinical experience, with the vertical prism adequately compensated, the horizontal will likely decrease at near if not disappear. That will certainly be the case with vertical prism and, as we expand vertical vergence ranges, we will look to progressively decrease the amount of vertical prism in Joseph’s Rx. But in Joseph’s case, at the outset, “less is more” did not apply.