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Prisms may alleviate diplopia over wide range of etiologies, types of misalignment
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Prisms proved effective in managing diplopia of varying etiologies and across a wide range of ocular misalignment, a study found.
“Our results indicate that prisms could be considered as initial management in patients with a wide range and variety of etiologies of ocular deviations, including larger and mixed strabismus, and do not have to be limited to smaller deviations,” the study authors said. “The decision to prescribe prisms should not be based simply on the amount of misalignment, but on other factors such as etiology, type of deviation, and degree of fusional amplitude.”
The retrospective cohort study included 94 patients who were prescribed prisms for con¬vergence and divergence insufficiency, skew devia¬tion, and decompensated phoria or tropia. Mean patient age was 68.7 years. Average follow-up was 15 months.
Thirty patients had divergence insufficiency, 14 had convergence insufficiency, nine had skew deviation and 41 had decompensated strabismus.
Prescribed prism power was based on the minimum necessary to eliminate diplopia in the primary gaze. Prism power equaling 50% of the deviation was increased or decreased according to fusional amplitudes. In most cases, a ground-in prism was prescribed binocularly and a Fresnel prism was prescribed monocularly.
Study results showed complete or partial resolution of double vision in 88% of patients.
Prisms were 100% effective in patients with divergence insufficiency and skew deviation, 85% effective in patients with decompensated strabismus and 64% effective in patients with convergence insufficiency.
Throughout the follow-up interval, prisms were continued in 89% of patients. However, 11% of patients chose to halt prism use and undergo strabismus surgery, the authors said.
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