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The orbit of the eye
Last reviewed: 04.07.2025
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The lacrimal, frontal, and trochlear nerves and the superior ophthalmic vein are located in the upper part of the orbit. The upper and lower branches of the oculomotor nerve, the abducens nerve, and the nasociliary and sympathetic fibers pass through the lower part.
The orbit of the eye is a pear-shaped cavity, the exit from which is represented by the optic nerve canal. Its intraorbital portion is longer (25 mm) than the distance from the posterior pole of the eye to the optic nerve canal (18 mm). This allows the eye to move forward a significant distance (exophthalmos) without excessive tension on the optic nerve.
- The orbital vault consists of two bones: the lesser wing of the sphenoid bone and the orbital plate of the frontal bone. The vault is adjacent to the anterior cranial fossa and frontal sinus. A defect in the orbital vault can cause pulsating exophthalmos by transmitting cerebrospinal fluid oscillations to the orbit.
- The outer wall of the orbit also consists of two bones: the zygomatic and the greater wing of the sphenoid. The anterior part of the eye protrudes beyond the outer edge of the orbit and is at risk of traumatic injury.
- The orbital floor is made up of three bones: the zygomatic, maxillary, and palatine. The posteromedial portion of the maxillary bone is relatively weak and can be subject to a "tear" fracture. The orbital floor forms the roof of the maxillary sinus, so a carcinoma growing into the orbit from the maxillary sinus can displace the eye upward.
- The inner wall of the orbit is made up of four bones: the maxillary, lacrimal, ethmoid, and sphenoid. The papillary plate, which forms part of the medial wall, is paper-thin and perforated with many openings for nerves and blood vessels, so orbital cellulitis often develops secondarily to ethmoid sinusitis.
- The superior orbital fissure is a narrow space between the greater and lesser wings of the sphenoid bone through which important structures pass from the cranial cavity into the orbit.
Inflammation in the area of the superior orbital fissure and the orbital apex manifests itself with a variety of symptoms, including ophthalmoplegia and impaired venous outflow, which causes the development of eyelid edema and exophthalmos.
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