Persistence of eye movement following disinsertion of extraocular muscle

BACKGROUND It is widely assumed that the insertion of the extraocular muscle is the sole site of force translation from muscle to eye. Our aim was to test this assumption by examining ocular motility after disinsertion of the extraocular muscle. METHODS Forty-two adults (age, 20-45 years; median age, 26 years) underwent strabismus surgery. All surgeries were completed under topical anesthesia with lidocaine 2\% jelly or peribulbar sensorimotor differential blocking anesthesia with ropivacaine 0.2\%. Sixty-six rectus muscles and six oblique muscles were suture-locked and disinserted. After disinsertion of each muscle, the patient was asked to move the eye in the field of action of the muscle; eye movement was recorded as normal, reduced, or absent. RESULTS For 50 rectus muscles (76\%), eye movement was normal after disinsertion, while for 14 rectus muscles (21\%), eye movement was reduced after disinsertion. For only two rectus muscles (3\%), eye movement was absent after disinsertion. For all six oblique muscles (100\%), eye movement was normal after disinsertion. CONCLUSIONS The unexpected, strong persistence of eye movement in the direction of action of the disinserted muscle indicates that anatomic insertion not only occurs at the point at which the muscle blends into the sclera but also involves the surrounding connective tissue. Orbital connective tissue can be considered an additional and important locomotor system.