2020–2021 BCSC Basic and Clinical Science Course™
2 Fundamentals and Principles of Ophthalmology
Part I: Anatomy
Chapter 1: Orbit and Ocular Adnexa
Orbital Anatomy
Orbital Floor
The floor of the orbit, which is the roof of the maxillary antrum (or sinus), is composed of 3 bones (Fig 1-4):
The infraorbital groove traverses the floor and descends anteriorly into the infraorbital canal. Both the groove and the canal house the infraorbital nerve (maxillary division of the trigeminal nerve, V2), which emerges at the infraorbital foramen, below the orbital margin of the maxillary bone. For this reason, patients evaluated for orbital floor fractures should also be assessed for infraorbital hypoesthesia.
Arising from the floor of the orbit just lateral to the opening of the nasolacrimal canal is the inferior oblique muscle, the only extraocular muscle that does not originate from the orbital apex. The floor of the orbit slopes downward approximately 20° from posterior to anterior. Before puberty, the orbital floor bones are immature and more prone to “trapdoor”-type fractures and secondary muscle entrapment.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.