Anatomy of the Orbit
The eyeball is safely lodged in a bony socket called the orbit on the two sides of the nose. The four-sided orbital cavity is pyramidal in shape with an open base in front and an apex on the back. The four walls of the orbit converge posteriorly to reach
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Anatomy of the Orbit
Keywords
Four-walled orbital cavity Bony socket for eyeballs Pyramidal shape Apex and base of orbit Paranasal sinuses Frontal ethmoidal Maxillary Roof Floor Lateral and medial walls of orbit Mucocele Proptosis
The eyeball is safely lodged in a bony socket called the orbit on the two sides of the nose. The four-sided orbital cavity is pyramidal in shape with an open base in front and an apex on the back. The four walls of the orbit converge posteriorly to reach the apex on their back formed by the optic foramen. The four walls are called the roof, floor, and medial and lateral walls. The lateral wall, which has a protective function, is the strongest. The medial wall is the thinnest and contains the ethmoidal sinuses with ethmoid air cells. There are three sinuses—anterior, middle, and posterior—on each side. They are liable to fracture with severe contusion injuries of the orbit, in which case air may enter the orbit and periorbital tissues, causing periorbital crepitus. Nasal bleeding may occur if the patient blows his or her nose. Another weak spot in the orbit is in its floor near the infraorbital groove. This changes into the infraorbital canal, which lodges the infraorbital nerves and vessels whose involvement may cause anesthesia of the upper lip in what is called a “blow-out fracture of the floor.” Three paranasal sinuses are present in the orbit: (1) the frontal in the superomedial part of the roof,
(2) the ethmoidal medially, and (3) the maxillary in the floor. In the blow-out fracture of the floor, herniation of the inferior oblique muscle and of some fat into the underlying maxillary sinus may occur. Diseases of these paranasal sinuses may affect the orbit secondarily, such as in orbital cellulitis in untreated ethmoiditis in children, and mucocele of the frontal sinus can cause downward and outward pushing of the eyeball. This is called oblique proptosis. Orbital space is limited to the orbit by the septum orbitale, and a growing mass will displace its normal contents in a direction opposite of the mass. A good example is mucocele of the frontoethmoidal sinus, which may displace the eyeball down and out.
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Basic Concepts
The four-walled bony orbital cavities form a sort of protective socket for each eyeball and are situated on the two sides of nose (Figs. 1.1 and 1.2; Table 1.1). It is in this bony socket, in which each eyeball is lodged along with its muscles, nerves, and blood vessels that are essential for its
© Springer International Publishing Switzerland 2016 M.W. Ansari and A. Nadeem, Atlas of Ocular Anatomy, DOI 10.1007/978-3-319-42781-2_1
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1 Anatomy of the Orbit
Fig. 1.1 The nose between two bony sockets (orbit)
Bony sockets of eyes on two sides of nose
called Orbits
Nose in between Right orbit
Left orbit
Fig. 1.2 The eyeball in its bony socket
Eyebrow
Eyelid
Pupil
Cornea Iris Sclera
Eyelid Nose
proper functioning. Above each orbit is the anterior cranial fossa, medially are the nasal cavity and ethmoid air sinuses
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