Superior rectus muscle overaction after cataract extraction.

Four patients with an ipsilateral hypertropia after cataract extraction consistent with superior rectus muscle overaction were identified between March 1990 and April 1992. Operative trauma was the most likely causative factor, as other likely conditions were excluded. The proposed pathogenesis for all cases is similar to that of botulinum type-A toxin therapy: a transient postoperative weakness of the ipsilateral inferior rectur muscle leads to a contracture or strengthening of the ipsilateral antagonist (the superior rectus muscle). Possible mechanisms of injury that would result in a transient inferior rectus muscle palsy would include anesthetic myotoxicity or direct trauma to the muscle and related structures from the retrobulbar injection (or subconjunctival injection). Surgical intervention consisting of an ipsilateral superior rectus muscle recession and posterior fixation sutures (when the vertical incomitance was large) yielded excellent results in restoring single binocular vision. Possible preventive measures would include using a minimal volume of anesthetic along with careful needle placement.