The orbit is the pyramid-shaped bony socket that houses the eyeball and its supporting structures. Its base opens onto the face and its apex points back toward the optic canal and superior orbital fissure. Besides the eye, it contains the extraocular muscles, orbital fat, the lacrimal gland, and the nerves and vessels serving them.
| Location | Paired bony cavities on either side of the root of the nose, below the anterior cranial fossa |
|---|---|
| Parts |
|
| Nerve Supply | Optic nerve (CN II); Oculomotor (CN III), trochlear (CN IV) and abducens (CN VI) nerves; Ophthalmic division of the trigeminal nerve (CN V1); Ciliary ganglion |
| Blood Supply | Ophthalmic artery; Infraorbital artery |
Protects the eyeball and provides a fixed frame and fat cushion within which the eye can rotate smoothly. It also channels the nerves and vessels that serve the eye.
The orbit is a closed space, so swelling or bleeding inside it can quickly raise pressure on the optic nerve. Orbital cellulitis, often spreading from the ethmoid sinus, causes painful eye movements, proptosis and reduced vision and needs urgent treatment. Blowout fractures of the thin floor or medial wall can trap the inferior rectus and cause double vision on looking up.
Bleeding or swelling within the orbit raises pressure enough to compress the optic nerve and its blood supply. Emergency lateral canthotomy and cantholysis can save vision.
Infection of the tissues behind the orbital septum, usually from adjacent sinusitis. It causes proptosis, painful restricted eye movement and fever, and can spread to the cavernous sinus.
Autoimmune swelling of the extraocular muscles and orbital fat, usually with Graves disease. It causes proptosis, eyelid retraction and, in severe cases, optic nerve compression.
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