Structure and Contents of the Orbit
- The orbit is the cavity or socket of the skull that contains the eye and its appendages.
- The volume of the orbit in adult humans is 30 millilitres, with the eye occupying 6.5ml.
- The orbital contents include the eye, extraocular muscles, cranial nerves II, III, IV, V, and VI, blood vessels, fat, lacrimal gland, eyelids, and ligaments.
- The orbit consists of a base, an apex, and four walls.
- The walls of the orbit are formed by seven bones, including the frontal, lacrimal, ethmoid, zygomatic, maxillary, palatine, and sphenoid bones.
Openings in the Orbit
- Important openings in the orbit include the supraorbital foramen, infraorbital foramen, superior orbital fissure, inferior orbital fissure, and optic canal.
- These openings contain structures crucial to normal eye functioning, such as nerves and blood vessels.
- The supraorbital foramen contains the supraorbital nerve, while the infraorbital foramen contains the infraorbital nerve.
- The optic canal contains cranial nerve II (optic nerve) and the ophthalmic artery.
- The superior orbital fissure is a pathway for intracranial communication and contains cranial nerves III, IV, VI, and ophthalmic branches of cranial nerve V.
Bony Walls of the Orbit
- The orbit is formed by a mosaic of seven embryologically distinct bones, including the zygomatic, sphenoid, maxillary, lacrimal, ethmoid, frontal, and palatine bones.
- The ethmoid bone forms the thinnest wall of the orbit, known as the lamina papyracea.
- The frontal bone forms the superior margin of the orbital rim.
- The orbital plate of the frontal bone and the lesser wing of the sphenoid form the roof of the orbit.
- The floor of the orbit is formed by the maxilla, zygomatic bone, and palatine bone.
Borders of the Orbit
- The base of the orbit, also known as the orbital margin, has four borders formed by different bones.
- The superior margin is formed by the frontal bone.
- The inferior margin is formed by the maxilla and zygomatic bone.
- The medial margin is formed by the frontal bone and maxilla.
- The lateral margin is formed by the zygomatic bone and frontal bone.
Function of the Orbit
- The main function of the orbit is to hold and protect the eyes.
- Eye movement is controlled by six extraocular muscles.
- The ophthalmic artery and superior ophthalmic vein are important blood vessels in the orbit.
- The optic canal contains the optic nerve, which is crucial for vision.
- The orbit also protects the eyes from mechanical injury.
In anatomy, the orbit is the cavity or socket/hole of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents. In the adult human, the volume of the orbit is 30 millilitres (1.06 imp fl oz; 1.01 US fl oz), of which the eye occupies 6.5 ml (0.23 imp fl oz; 0.22 US fl oz). The orbital contents comprise the eye, the orbital and retrobulbar fascia, extraocular muscles, cranial nerves II, III, IV, V, and VI, blood vessels, fat, the lacrimal gland with its sac and duct, the eyelids, medial and lateral palpebral ligaments, cheek ligaments, the suspensory ligament, septum, ciliary ganglion and short ciliary nerves.
| Orbit | |
|---|---|
 Diagram of eye with surrounding superior, oblique, medial and inferior rectus muscles; supraorbital foramen shown above the eye, and inferior orbital fissure inferolaterally. | |
| Details | |
| Identifiers | |
| Latin | orbita |
| MeSH | D009915 |
| TA98 | A02.1.00.067 |
| TA2 | 469 |
| FMA | 53074 |
| Anatomical terminology | |
