INFERIOR OBLIQUE MUSCLE INJURY FROM LOCAL-ANESTHESIA FOR CATARACT-SURGERY

Background: Vertical rectus muscle injury is commonly cited as a cause of strabismus after cataract surgery. Injury to the inferior oblique muscle or nerve as a complication of cataract surgery has not been des cribed previously. Methods: Four patients without pre-existing strabis mus who had diplopia after cataract surgery were studied. Analysis inc luded prism and cover testing, Lancaster red-green testing, and fundus torsion assessment. Results: Three patients had a delayed-onset hyper tropia with fundus extorsion in the eye that underwent surgery, which is consistent with inferior oblique muscle over-action secondary to pr esumed contracture. The fourth patient had an immediate-onset hypotrop ia with fundus intorsion in the eye that underwent surgery, which is c onsistent with inferior oblique muscle paresis. Damage to a vertical r ectus muscle or ''unmasking'' of a pre-existing superior oblique muscl e paresis could not explain the history and findings in this group of four patients. Conclusion: The inferior oblique muscle contracture obs erved in three patients may have been caused by local anesthetic myoto xicity, whereas the paresis observed in one patient may have been due to mechanical trauma or anesthetic toxicity directly to the nerve inne rvating the muscle. Inferior oblique muscle or nerve injury should be considered as another possible cause of postoperative strabismus, espe cially when significant fundus torsion accompanies a vertical deviatio n.