The orbit and its contents

Abstract The function of the orbit is to protect and accommodate the globe in order to maximise its function. The bony orbits are paired four-sided conical cavities within the skull each comprising seven bones – ranging from the paper thin ethmoid and lacrimal plate medially to the buttress thick zygoma laterally. The conical shape consists of an apex posteriorly and a base anteriorly forming the outer margin. The medial wall and floor begin to blend towards the apex forming a posteromedial bulge as the orbit takes on a three-walled pyramidal structure. The walls are lined by periosteum (periorbita), which is continuous with the periosteal layer of the dura mater at the apex, the orbital septa and the fascial sheaths of the extraocular muscles. There are five principal openings of the orbit – three principal foramina located at the apex that transmit the neurovascular supply of the orbit and two lesser foramina located on the medial wall.