THE EFFECT OF EDROPHONIUM CHLORIDE ON MUSCLE BALANCE IN NORMAL SUBJECTS AND THOSE WITH NONMYASTHENIC STRABISMUS

Because the Lancaster red-green test and the Hess screen are not widel y used by most ophthalmologists, we used the alternate prism-cover tes t to study the effect of intravenous edrophonium chloride (Tensilon) o n the ocular alignment of 30 normal subjects and 14 individuals with n onmyasthenic strabismus. After measurement of their baseline phorias a nd tropias, patients received an intravenous injection of Tensilon via the incremental dose technique until autonomic effects of the drug we re 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 hal f of the nonmyasthenic strabismics, however, showed a change in their vertical deviation after Tensilon (46% at distance and 38% at near), w ith the majority of them increasing their angle of squint. These chang es were small (mean, 1.7 prism diopters; maximum, 5 prism diopters). I n only one case did reversal of the direction of deviation occur. Tens ilon produces a statistically significant increase in near exophorias of normal subjects and in vertical distance deviations of nonmyastheni c strabismics. These changes, however, are clinically insignificant an d should not be considered to constitute a positive Tensilon test.