Superior oblique tenectomy in a pattern strabismus.

Nineteen patients with A pattern exotropia and 1 with A esotropia, all of whom had marked overacting superior oblique muscles bilaterally, were evaluated surgically. Nine with A exotropia and 20 prism diopters or less in the primary position were treated only with bilateral superior oblique tenectomy. Very little correction occurred in the primary position while an average correction of 35 prism diopters occurred in downgaze. Eleven patients with at least 25 prism diopters of deviation in the primary position were treated with bilateral superior oblique tenectomy in addition to horizontal rectus muscle surgery at the same sitting. A routine amount of horizontal surgery was performed with good results without regard for any effect which superior oblique tenectomy might cause in the primary position. This is a safe method for planning surgery in A patterns as abduction by the superior oblique muscles occurs mainly in downgaze.