Anterior transposition of the inferior oblique. Anatomic assessment of the neurovascular bundle.

Anterior transposition of the inferior oblique insertion has been described as an effective procedure for weakening the inferior oblique and for decreasing dissociated vertical deviation. It has been postulated that this occurs by converting the inferior oblique muscle from an elevator to a depressor. We found histologic, radiologic, and clinical evidence that anterior transposition of the inferior oblique muscle converts it to a depressor by means of the firm posterior attachment of the inferior oblique muscle at the site of its neurovascular bundle. This new functional insertion at the neurovascular bundle created by the anterior transposition allows for the depressor effect seen after this procedure.