A New Classification of Superior Oblique Palsy Based on Congenital Variations in the Tendon

Background: Superior oblique palsy is the most frequent isolated cranial nerve palsy seen in strabismus practice. It is traditionally diagnosed according to etiology as acquired, congenital, or idiopathic, but surgical treatment is based on deviation not etiology. Observations at surgery led to speculation that the superior oblique tendon is different in congenital compared with acquired superior oblique palsy and that this difference should be considered in surgical treatment. Methods: The authors reviewed the charts of 82 patients (89 eyes) undergoing surgery on the superior oblique tendon for superior oblique palsy. In each case, the palsy had been diagnosed preoperatively as acquired, congenital, or idiopathic, and, at surgery, characteristics of the tendon anatomy were described. Results: Thirty-eight superior oblique tendons (36 patients), diagnosed as congenital superior oblique palsy, included 33 abnormal tendons and 5 normal tendons. Twentyfour tendons (21 patients), diagnosed as traumatic superior oblique palsy, included 22 normal and 2 abnormal tendons. Twenty-seven tendons (25 patients), diagnosed as idiopathic, included 19 normal and 8 abnormal tendons. Abnormal tendons were divided into 4 categories: (1) redundant, (2) misdirected, (3) inserted in posterior Tenon's capsule, and (4) absent. Conclusions: The authors conclude that congenital superior oblique palsy is usually associated with a structural abnormality of the superior oblique tendon (87%). Whereas acquired superior oblique palsy usually has a normal tendon (92%). Superior oblique underaction in acquired superior oblique palsy results from a neural deficit. Potential variance in anatomy of the superior oblique tendon should be considered when undertaking surgery for superior oblique palsy.