Walls of orbit

• Orbits are pyramidal bony cavities, situated one on each side of the root of nose.
• They provide sockets for rotatory movements of eyeball.
• Orbit is four-side pyramid with an apex, a base and four walls.                             

SUPERIOR WALL OF ORBIT

• The superior wall (roof) is formed primarily by the orbital plate of frontal bone, and the lesser wing of sphenoid.
• The orbital surface presents medially by trochlear fovea and laterally by lacrimal fossa.

INFERIOR WALL OF ORBIT

• The  inferior wall (floor) is formed by the orbital surface of maxilla, the orbital surface of zygomatic bone and orbital process of palatine bone.
• Medially, near the orbital margin, is located the groove for nasolacrimal duct.
• Near the middle of the floor, located infraorbital groove, which leads to the infraorbital foramen.
• The floor is separated from the lateral wall by inferior orbital fissure, which connects the orbit to pterygopalatine and infratemporal fossa.
• Haller cells are seen in Orbital Floor.
• Some of the ethmoidal air cells which invade the floor of the orbit are called haller cells.
• Lines of Sebileau pass through Floor of orbit and maxillary antrum.
• Used in the Ledermann’s classification of maxillary carcinoma.

MEDIAL WALL OF ORBIT

• Medial orbital wall is formed by frontal process of maxilla, lacrimal bone, ethmoid bone (orbital plate) and body of sphenoid bone.
• It is the thinnest (weakest) wall of the orbit.
• The thinnest portion of medial wall of orbit is the lamina papyracea which separates ethmoid sinuses from orbit.

LATERAL WALL OF ORBIT

• The lateral wall is formed by the frontal process of zygomatic and orbital plate of the greater wing of sphenoid.
• The lateral wall is the thickest wall of the orbit, important because it is the most exposed surface, highly vulnerable to blunt force trauma.

CLINICAL SIGNIFICANCE OF ORBITAL WALLS.

1. Blow out fracture of Orbit:

• Blow out fractures mainly involve orbital floor and medial wall (Most commonly Posterior-medial wall of floor).
• The most common bone fractured is the maxillary bone which comprises the floor of the orbit. 
• The orbital contents can be significantly displaced inferiorly after orbital blowout fracture.
• Clinical Features are: Enophthalmos,Diplopia,Restriction of eye movements and Hypaesthesia (Reduced sense of touch or sensation) which is due to injury of infraorbital nerve.
• Diplopia in both up & down gaze (double diplopia).
• Backward traction is due to entrapped inferior rectus.
• Enophthalmos is caused by fracture of floor of orbit.
• Escape (herniation) of orbital fat into maxillary sinus.
• Restriction movements occur due to entrapment of Inferior rectus & Inferior oblique and Medial Rectus.Orbital emphysema is most common in medial wall fractures.
• Specially vertical, and adduction & abduction movements restricted.
• Confirmed by ‘positive forced duction test’.
• Investigation: Radiograph (Waters view) may see a soft tissue mass on the superior margin of the maxillary sinus.
• Hanging drop or tear drop sign: hanging opacity of superior maxillary antrum.

Management:

• Small cracks & fractures involving less than half of the orbital floor with little or no herniation & improving diplopia do not require treatment unless more than 2mm enopthalmos develop.
• Fractures involving half or more orbital floor with entrapment of orbital contents & persistent diplopia in the primary position should be repaired with in 2 weeks.

2. Fracture of roof of orbit:

•  The most common cause of fracture of roof of orbit is Blow on the forehead.
• Often associated with a late-developing periorbital hematoma.
• Severe fractures of the orbital roof often are associated with fractures of the forehead combined with brain injury and dural tears with cerebrospinal fluid leakage.
• Unilateral lacrimal gland destruction may be caused by fracture of roof of Orbit.