Medial transposition of the lateral rectus muscle in experimentally induced medial rectus paralysis

When the oculomotor nerve is completely paralyzed, the affected eye shows severe outward displacement and poor cosmetic appearance. Past results of many surgical procedures for oculomotor palsy have been generally unsatisfactory. We tried a new surgical approach experimentally, in which the disinserted lateral rectus muscle was used as an adductor by medial transposition of the muscle. Five adult cats underwent disinsertion of the medial rectus muscle of both eyes to induce iatrogenic medial rectus paralysis. The disinserted medial rectus was removed as far back as possible to prevent reattachment. Then, the right lateral rectus muscle was disinserted and passed beneath the superior rectus muscle and resutured to the sclera 4mm superoposterior to the medial rectus insertion site. After excision of the bilateral medial rectus, a large exotropia of an average 47.6 delta (42.0-55.5 delta) was induced. The medial transposition of the right lateral rectus produced an average 36.6 delta (24.8-45.8 delta) correction of the exotropia. A satisfactory cosmetic result was achieved by this procedure.