Orbital Anatomy and Nerves

Orbital Region

• The orbit, a bony cavity, houses the eyeball and its muscles.
• Surrounding structures include orbital fat, fascia, vessels, and nerves.

Orbital Bones

• The orbital region is comprised of seven bones: frontal, sphenoid, ethmoid, lacrimal, zygomatic, palatine, and maxillary.
• The orbit boasts four walls (superior, inferior, medial, and lateral), along with openings for nerves and vessels.

Nerves of the Orbital Region

• Ophthalmic division of the trigeminal nerve (CN V1): responsible for sensory innervation of the orbit.

• Lacrimal nerve: innervates the lacrimal gland and conjunctiva.

• Frontal nerve: provides sensory innervation to the forehead and scalp.

• Nasociliary nerve: provides sensory innervation to the nasal cavity, iris, and cornea.

• Oculomotor nerve (CN III): controls most of the extraocular muscles, responsible for pupillary constriction and accommodation.

• Trochlear nerve (CN IV): innervates the superior oblique muscle, allowing for downward and outward eye movement.

• Abducent nerve (CN VI): innervates the lateral rectus muscle, responsible for lateral eye movement.

• Sympathetic fibers: innervate the dilator pupillae muscle, causing pupillary dilation.

• Parasympathetic fibers: via the oculomotor nerve, control the sphincter pupillae muscle (pupillary constriction), and the ciliary muscle (lens accommodation).

Blood Supply of the Orbital Region

• Ophthalmic artery: the primary artery supplying the orbit, branching off the internal carotid artery.
• The ophthalmic artery gives rise to several branches, including the central retinal artery and the superior and inferior muscular branches.

Venous Drainage of the Orbital Region

• The orbit is drained by the superior and inferior ophthalmic veins, which eventually empty into the cavernous sinus.

Lacrimal Apparatus

• The lacrimal gland produces tears, which are essential for lubrication and protection of the eye.
• Tears flow through the lacrimal canaliculi, then into the nasolacrimal duct, and ultimately drain into the nasal cavity.

Fascia of the Eye

• The orbital fascia provides support and structure for the eye and its associated muscles.
• There are two main types of fascia:
  • Orbital fascia: surrounds the entire orbit.
  • Bulbar fascia: surrounds the eyeball and the extraocular muscles.

Orbital Fat

• Orbital fat acts as a cushion and insulator for the eyeball, and helps to maintain the shape of the orbit.

Eyelids

• The eyelids provide protection for the eyeball and assist in tear film distribution.
• Composed of skin, muscles, and tarsal plates.

Extra-ocular Muscles (EOM)

• Six extraocular muscles control eye movement:
  • Rectus muscles (4): superior, inferior, medial, and lateral rectus.
  • Oblique muscles (2): superior and inferior oblique.

Intrinsic Muscles of the Orbital Region

• Sphincter pupillae: constricts the pupil (parasympathetic via CN III).
• Dilator pupillae: dilates the pupil (sympathetic via nasociliary nerve).
• Ciliary muscle: controls the shape of the lens for accommodation (parasympathetic, CN III).

Explore the intricate structures of the orbital region, including its bones, nerves, and surrounding elements. This quiz will test your knowledge on the anatomy of the orbit and the roles of various cranial nerves in ocular function.