Fig. 12. Congenital agenesis of the 6th nerve (Duane’s retraction syndrome, type I) in a 5-year-old boy.

A. Axial high-resolution T2 image showing a normal left 6th nerve (arrow). The right 6th nerve was not observed. B. Axial thin-section post-contrast T1 image shows atresia of the right Dorello’s canal (arrow), compared with the normal left side (arrow). C. Orbital coronal T2 image shows symmetrical size of the bilateral lateral recti (arrows). The volume of the lateral rectus is preserved because of aberrant innervation from the 3rd nerve in this disease. D. This is different from acquired 6th nerve palsy. Gaze photograph showing impaired abduction of the right eye. X = interruption of eye movement