The Orbit & The Eye

Introduction

The orbit is a pair of bony cavities in the skull that house and protect the eyeballs and associated structures. Understanding the anatomy of the orbit and the eye is essential for comprehending visual function and the protection of ocular structures.

The Orbit

General Structure

• Definition: The orbit is a pyramidal-shaped cavity in the skull, opening anteriorly to the face and guarded by the eyelids.

• Main Features: Each orbit has a base (orbital opening), an apex, and four walls (roof, floor, medial wall, lateral wall).

Base of the Orbit

• Orbital Opening: The base opens anteriorly in the face.

• Margins:

  • Superior: Formed by the frontal bone.

  • Inferior: Formed by the maxilla (medially) and the zygomatic bone (laterally).

  • Medial: Composed of the maxillary process of the frontal bone and the frontal process of the maxilla.

  • Lateral: Formed by the zygomatic process of the frontal bone and the frontal process of the zygomatic bone.

Apex of the Orbit

• Location: The apex corresponds to the optic canal, which transmits the optic nerve and ophthalmic artery.

Walls of the Orbit

• Roof: Mainly formed by the orbital plate of the frontal bone.

• Floor: Formed by the orbital plate of the maxilla, which separates the orbit from the maxillary sinus. Also includes the maxillary process of the zygomatic bone.

• Medial Wall: Composed of the frontal process of the maxilla, lacrimal bone, body of sphenoid, and orbital plate of ethmoid.

• Lateral Wall: Formed by the frontal process of the zygomatic bone and the greater wing of the sphenoid.

Key Openings in the Orbit

• Optic Canal: Transmits the optic nerve and ophthalmic artery.

• Superior Orbital Fissure: Passage for cranial nerves III, IV, V1, VI, and the superior ophthalmic vein.

• Inferior Orbital Fissure: Passage for the maxillary nerve, zygomatic branch, inferior ophthalmic vein, and sympathetic nerves.

• Nasolacrimal Canal: Transmits the nasolacrimal duct to the inferior meatus of the nose.

• Supraorbital Notch: Transmits the supraorbital nerve and vessels.

• Infraorbital Groove & Canal: Transmits the infraorbital nerve and vessels.

Functions and Clinical Relevance

• Protection: The bony orbit protects the eye from trauma.

• Support: Provides attachment for extraocular muscles, nerves, and vessels.

• Clinical Note: Fractures of the orbital floor (blowout fractures) can affect the maxillary sinus and infraorbital nerve.

Example: Orbital Fracture

A fracture of the orbital floor may result in herniation of orbital contents into the maxillary sinus, leading to diplopia (double vision) and infraorbital nerve damage.

Additional info: The orbit also contains orbital fat, ligaments, fascia, the lacrimal apparatus, and is traversed by several cranial nerves and blood vessels essential for ocular function.