Relieving Prism, Non Prism Glasses Show Similar Intermittent Exotropia Control

Base-in relieving prism spectacles do not demonstrate better distance control in children with intermittent exotropia compared with refractive correction without prism, according to a study published in Optometry and Vision Science. 

“Relieving prism treatment is prescribed for intermittent exotropia with the rationale of potentially restoring, improving, or maintaining normal binocular vision by optically reducing the fusional convergence demand, and thus making it easier to sustain
fusion,” the study authors explain. “If prism treatment results in better control of the intermittent exotropia and facilitates enhanced binocular fusion, thereby reducing the need for surgical or vision therapy/orthoptic treatment, there could be significant cost savings.”

Researchers included 57 children (58% girls; mean age, 6.6 years; mean baseline distance control 3.5 points) with distance intermittent exotropia in the investigation. Children who met the enrollment criteria, which included an Intermittent Exotropia Office Control Scale score of 2 or greater (0, phoria; 5, constant), 1 or more episodes of spontaneous exotropia, and between 16 and 35 prism diopters by prism-and-alternate cover test, underwent random assignment to treatment with base-in relieving prism (n=28) or non prism spectacles with refractive correction(n=25). 

Participants treated with the relieving prism wore their refractive correction and base-in prism equal to 40% of the larger of the distance and near exodeviations. The study’s purpose was to determine whether the results would warrant a full-scale clinical trial.

After 8 weeks, the mean intermittent exotropia distance control was 3.6 and 3.8 in the relieving prism and non prism groups, respectively. Mean distance control changes were 0.1 and −0.2 in the prism and non prism groups, respectively. The adjusted difference of 0.3 points (95% CI, −0.5-1.1) favored non prism, which did not allow the investigators to proceed to a full-scale clinical trial. 

“Our findings suggest that a 0.75-point or larger favorable effect on distance control is unlikely with our prism prescribing protocol,” according to the researchers. “It is unknown whether results might differ with other prism-prescribing regimens or with different eligibility criteria.”

Study limitations include a small sample size and convenience sampling.