The orbital floor is the bottom wall of the eye socket, a cone-shaped bony cavity that houses and protects the eyeball and associated structures. This structure, known as the orbit, is positioned directly above the cheekbone and the large air space of the maxillary sinus. The floor acts as a shelf that supports the eye, separating the delicate contents of the eye socket from the sinus below. Its vulnerability makes it a common site of injury following blunt force trauma to the face.
Anatomy and Composition
The orbital floor is formed by three different bones: the orbital plate of the maxillary bone, which makes up the largest portion; the zygomatic bone (cheekbone), which contributes to the front and outer edge; and the palatine bone at the rear of the socket.
This floor is the shortest and thinnest of the four orbital walls, contributing directly to its susceptibility to fracture. The bone is particularly thin near the center, just medial to the infraorbital canal. Forces impacting the eye are often redirected here, causing it to fail before the stronger bones of the orbital rim.
The entire floor structure forms the roof of the large air-filled maxillary sinus. A channel known as the infraorbital canal runs through the floor, carrying the infraorbital nerve and blood vessels. This close anatomical relationship means a break can easily involve the sinus space and damage the nerve contained within the canal.
Understanding Orbital Floor Fractures
A break in the orbital floor is commonly described as a “blowout fracture,” a term defining the mechanism of injury. This fracture occurs when a blunt object, such as a fist or a ball, strikes the eyeball, not the thick bony rim. The impact momentarily deforms the globe, leading to a sudden, dramatic increase in the pressure inside the socket.
Since the orbital contents cannot be compressed, this hydraulic pressure is transmitted outward to the surrounding bony walls. The thin orbital floor acts like a pressure relief valve, buckling downward into the maxillary sinus below. This causes the bone to fracture without the orbital rim being broken.
Fractures are described based on whether the break is isolated to the thin walls or involves the thicker orbital rim. A pure blowout fracture means only the thin floor has broken, while an impure fracture extends to the thicker supportive bone of the rim. The delicate tissues and fat from the eye socket can prolapse through the defect into the sinus cavity.
Recognising Signs of Injury
A common sign of an orbital floor fracture is double vision (diplopia). This symptom occurs because soft tissues, specifically the inferior rectus muscle responsible for moving the eye up and down, can become trapped within the fractured bone segments. When the muscle is caught, its movement is restricted, particularly when attempting to look upward or downward.
Another noticeable sign is enophthalmos, the sunken appearance of the injured eye. This occurs because the fracture increases the volume of the bony socket, allowing the eyeball and surrounding fat to drop slightly backward and downward. The sinking may be subtle initially due to swelling but becomes more apparent as inflammation subsides.
Numbness in the cheek, upper lip, and upper gum area is a consequence of this injury. This loss of sensation results from damage or compression of the infraorbital nerve, which runs along the floor within the bony canal. Bruising around the eye (ecchymosis) and significant swelling of the eyelid are also standard findings.
Repairing the Damage
The decision to repair an orbital floor fracture depends on several factors, including the size of the defect and the presence of functional problems like muscle entrapment or significant eye sinking. Small, non-displaced fractures that do not cause double vision may be monitored closely by a medical professional. This observation period allows initial swelling to decrease, which can sometimes resolve minor symptoms.
Surgical intervention is recommended when there is persistent double vision caused by muscle entrapment or when the eye is sunken more than two millimeters compared to the uninjured side. The primary goal is to free any trapped tissue, particularly the inferior rectus muscle, from the fracture site. Once the tissue is released, the broken orbital floor is reconstructed.
Surgeons use various materials to bridge the defect and restore the original contour of the socket, including thin metal plates, synthetic polymers, or absorbable sheets. The newly placed material acts as a barrier, preventing orbital contents from falling back into the sinus and supporting the eyeball in its correct position. Timely diagnosis and follow-up are important to minimize the long-term risk of vision problems and facial asymmetry.