Nine patients had a permanent paresis of a vertical rectus muscle after cataract extraction. We sought to determine the common factors associated with and their contribution to vertical muscle paresis after cataract extraction. The study design included a survey that was conducted among the referring cataract surgeons and anesthesiologists with particular attention to surgical technique and anesthetic administered, as well as a medical history and examination and appropriate laboratory tests. Patients had a complete ophthalmic examination including prism cover testing in all nine diagnostic positions, forced-duction testing, and saccadic velocity and generated muscle force estimation. The results of the study demonstrate no correlation between the pareses and the use of a bridle suture, antibiotic or corticosteroid injection, systemic disease, or surgical technique. Peribulbar anesthesia was the most consistent feature in seven of the nine cases. In the other two, an atypical retrobulbar injection had been given. On the basis of the location of the injections, the needle type, and the concentration and quantity of the anesthetic injected, we conclude that permanent pareses of a vertical rectus muscle may be caused by a myotoxic effect of the local anesthetic.