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):

• orbital plate of the maxillary bone

• palatine bone

• orbital plate of the zygomatic bone

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.

Figure 1-3 Right medial orbital wall. The medial orbital wall is formed by 4 bones: (1) maxillary (frontal process); (2) lacrimal; (3) lesser wing of the sphenoid bone; and (4) orbital plate of the ethmoid. The largest component of the medial wall is the lamina papyracea of the ethmoid bone. Superiorly, the anterior and posterior foramina at the level of the frontoethmoidal suture transmit the anterior and posterior ethmoidal arteries, respectively. The anterior medial orbital wall includes the fossa for the lacrimal sac, which is formed by both the maxillary and lacrimal bones. The lacrimal bone is divided by the posterior lacrimal crest. The anterior part of the lacrimal sac fossa is formed by the anterior lacrimal crest of the maxillary bone.

(Illustration by Dave Peace.)

Figure 1-4 Right orbital floor. The orbital floor is composed of 3 bones: (1) maxillary bone; (2) orbital plate of zygomatic bone; and (3) palatine bone. The nasolacrimal duct sits in the anterior middle area of the orbital floor, medial to the origin of the inferior oblique muscle.

(Illustration by Dave Peace.)

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.

• Wei LA, Durairaj VD. Pediatric orbital floor fractures. J AAPOS. 2011;15(2):173–180.

Figure 1-5 Right lateral orbital wall. The lateral orbital wall is formed by the zygomatic bone and the greater wing of the sphenoid bone. The junction between the lateral orbital wall and the roof is represented by the frontosphenoid suture. Posteriorly, the wall is bordered by the inferior and superior orbital fissures. The sphenoid wing makes up the posterior portion of the lateral wall and separates the orbit from the middle cranial fossa. Medially, the lateral orbital wall ends at the inferior and superior orbital fissures.

(Illustration by Dave Peace.)

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.