The Effect of Edrophonium Chloride on Muscle Balance in Normal Subjects and Those with Nonmyasthenic Strabismus

Abstract

Because the Lancaster red-green test and the Hess screen are not widely used by most ophthalmologists, we used the alternate prism-cover test to study the effect of intravenous edrophonium chloride (Tensilon) on the ocular alignment of 30 normal subjects and 14 individuals with nonmyasthenic strabismus. After measurement of their baseline phorias and tropias, patients received an intravenous injection of Tensilon via the incremental dose technique until autonomic effects of the drug were noted or until 10 mg was administered. Another set of measurements of muscle balance was taken immediately postinjection and 2 and 5 min later. Apart from a small increase (mean, 2 prism dipoters; p = 0.004) in their exophoria at near, normal subjects exhibited no significant change in their phorias after Tensilon injection. One third to one half of the nonmyasthenic strabismics, however, showed a change in their vertical deviation after Tensilon (46% at distance and 38% at near), with the majority of them increasing their angle of squint. These changes were small (mean, 1.7 prism diopters; maximum, 5 prism diopters). In only one case did reversal of the direction of deviation occur. Tensilon produces a statistically significant increase in near exophorias of normal subjects and in vertical distance deviations of nonmyasthenic strabismics. These changes, however, are clinically insignificant and should not be considered to constitute a positive Tensilon test.