Embryology of extraocular muscles : A new vision

Purpose To describe the embryology of extraocular muscles, through a 3D viewing algorithm, from Carnegie stage XVII to Carnegie stage XXIII (41st-57th day of development). Methods The work consisted of a scanning and a data processing reconstruction of embryonic histological material. Material came from anatomical universities collections. 12 embryos were selected, and 7 were dedicated to muscle study (from 14.5mm to 54.5mm). This data processing has allowed a study in three spatial planes. Results From Carnegie stage XVII, all extraocular muscles are in place, including levator palpebrae. The study in 3 planes makes their individualization easier. Gilbert (Carnegie Institution) described the origin of inferior rectus and inferior oblique by a common primordium, however from the stage XVII the two muscles are clearly separated. The decussation of the superior oblique is seen from the stage XIX, the trochlea appears at stage XXII. Our work also demonstrates the nerves : optic, oculomotor, trochlear, trigeminal and abducens. The junctions between nerve and muscle are put in evidence, especially for the lower branch of the oculomotor nerve. Conclusion This new study tool has resulted in explicit images of the development of extraocular muscles in the embryonic period. It helped to provide details with respect to the work already established by the Carnegie Institution.