Prescribing Relieving Prism for Kelly A. Frantz, on, F AAO, FCOVD Patients with Disorders

Patients with or nonstrabismic binocular disorders can, in certain cases, be managed using spectacle prism that partially or to- tally neutralizes the ocular deviation. Conditions particularly amenable to relieving prismatic prescription include basic exo- and esophoria, di- vergence insufficiency, vertical phoria, and strabismus with normal sen- sory fusion. A prismatic prescription can be determined using Sheard's criterion, Saladin's 1:1 rule, disparity testing, associated phoria measurement, neutralization, or residual vergence demand cri- teria. Prescribing prism for patients with noncomitant strabismus re- quires special diagnostic and management considerations. The likelihood of prism adaptation in certain patients must be considered, and methods of detection are discussed. Two case reports present examples of patients whose management included prescription of relieving prism. Key Words: prism, spectacles, binocular vision, fusion, strabismus, f/.Xation disparity, associated phoria, Sheard's criterion.

INTRODUCTION prescribed. Thus, relieving prism that reduces the demand on the vergence system without The decision to prescribe spectacle prism eliminating the deviation completely,l is often for a patient must be made carefully after preferred. Whenever possible, the goal should thorough diagnostic testing. U sed wisely, be to reduce the amount of prism worn over a prism can sometimes significantly improve a period of time as the patient is able to develop patient's comfort by relieving diplopia and/or improved motor fusion ability through a vision asthenopia. For a patient possessing normal therapy program. While acknowledging that sensory fusion {normal correspondence and prism is a very useful tool as part of vision little suppression), prism can be used to par- therapy, this review will concentrate on pre- tially or totally neutralize a phoric or strabis- scription of relieving prism in spectacles. mic angle that is too large to allow comfortable Obviously, there are certain drawbacks to and efficient fusion. The minimum amount of the use of spectacle prism. First, several con- prism that allows comfortable fusion should be ditions are not addressed by a prism prescrip- tion. Prism prescriptions do not substitute for Correspondence to Kelly A. Frantz, Illinois Col- in treating suppression, oculo- lege of Optometry, Chicago, Illinois. motor, accommodative, and vergence facility

54 Journal of Optometric Vision Development