Anomalous posterior insertion of medial rectus muscle simulating congenital oculomotor palsy

An unusual case was examined in our Hospital showing severe exotropia with adduction palsy. However, during surgery, anomalous posterior insertion of the medial rectus muscle was found, and the Hummelsheim operation was performed to correct the exotropia. To the best of the authors' knowledge, this is the first report of anomalous posterior insertion of the medial rectus muscle as a cause for congenital exotropia with adduction palsy.