Inferior orbital fissure

Inferior orbital fissure is an important anatomic structure located in the skull that plays a crucial role in the functioning of the eye and surrounding structures.^[3]

Structure

The inferior orbital fissure is a narrow, slit-like opening that is located in the orbital bone (also known as the eye socket) of the skull. It is positioned between the maxillary bone and the sphenoid bone and is situated inferior (below) to the superior orbital fissure. The inferior orbital fissure is bordered by the orbital floor medially, the orbital wall laterally, and the roof of the maxillary sinus superiorly.^[1] It is triangular in shape and is wider at the base than at the apex. The inferior orbital fissure has two parts: the anterior part and the posterior part. The anterior part is located closer to the front of the face and is wider and more triangular in shape. The posterior part is located closer to the back of the skull and is narrower and more elongated. The inferior orbital fissure is lined by a thin layer of smooth muscle called the orbitalis muscle. This muscle helps to protect the structures passing through the fissure by closing the fissure when necessary.

Location

The inferior orbital fissure is located in the orbital bone of the skull, which is the bone that forms the eye socket. ^[8]It is positioned between the maxillary bone and the sphenoid bone and is situated inferior (below) to the superior orbital fissure. The inferior orbital fissure is located on the lateral (outer) side of the face, just below the orbit (eye). It can be easily located by feeling for the depression below the orbit.

Function

The inferior orbital fissure serves as a passageway for several important structures in the head and neck. These structures include:

• The infraorbital nerve: This is a branch of the maxillary nerve that supplies sensation to the skin of the lower eyelid, cheek, and upper lip. It passes through the inferior orbital fissure and exits the skull through the infraorbital foramen, which is located on the orbital floor just below the inferior orbital fissure.^[6]
• The infraorbital artery: This is a branch of the internal maxillary artery that supplies blood to the skin and muscles of the lower eyelid, cheek, and upper lip. It passes through the inferior orbital fissure and exits the skull through the infraorbital foramen.
• The nasolacrimal duct: This is a small tube that drains tears from the eye into the nasal cavity. ^[5]It passes through the inferior orbital fissure and enters the nasal cavity through the nasolacrimal canal, which is located on the orbital floor just below the inferior orbital fissure.
• The zygomaticofacial nerve: This is a branch of the zygomatic nerve that supplies sensation to the skin of the cheek. It passes through the inferior orbital fissure and exits the skull through the zygomaticofacial foramen, which is located on the orbital floor just below the inferior orbital fissure.^[4]

Clinical Significance

The inferior orbital fissure is important for several reasons in clinical practice. Some of the clinical conditions related to the inferior orbital fissure are as follows:

• Fractures: The inferior orbital fissure can be fractured as a result of trauma to the eye socket, such as a blow to the face or a car accident. A fracture of the inferior orbital fissure can cause damage to the structures passing through it, leading to numbness or weakness in the cheek and upper lip, as well as double vision and difficulty moving the eye.^[7]
• Infections: The inferior orbital fissure is prone to infections due to its close proximity to the sinuses and nasal cavity. Infections of the inferior orbital fissure can cause pain and swelling in the cheek and eye, as well as a discharge from the nose.
• Tumors: Tumors can grow in the area around the inferior orbital fissure, such as the orbital floor or the cheek. These tumors can cause swelling and pressure on the eye, leading to vision loss or other problems with eye movement.
• Sinusitis: The inferior orbital fissure is located near the maxillary sinus, which is one of the paranasal sinuses.^[2] Inflammation of the maxillary sinus (sinusitis) can cause pain and swelling in the cheek and eye, as well as a discharge from the nose.