The orbit, commonly known as the eye socket, is a protective bony cavity within the skull housing the eyeball and its associated structures. Shaped like a four-sided pyramid, its bony walls shield the sensory organ from external force. The orbital floor is the lowest wall of this cavity, forming a distinct boundary that separates the eye socket contents from the air-filled spaces below. It serves as a foundational platform for the globe.
Anatomical Components of the Orbital Floor
The inferior wall of the orbit is primarily composed of three bones. The largest contribution comes from the orbital surface of the Maxillary bone, which forms the central portion of the floor. This is supplemented by the Zygomatic bone (cheekbone), which contributes to the anterolateral section. A smaller part is completed posteriorly by the orbital process of the Palatine bone.
This arrangement creates a structure that is notably thinner than the other orbital walls. The orbital floor also serves as the roof of the Maxillary sinus, a large air-filled cavity located below the eye. This close anatomical relationship means the floor is subject to the conditions of the sinus space. The thinness of the bone, particularly the posteromedial section, contributes to its vulnerability.
Functional Significance of the Orbit’s Base
The orbital floor provides essential support for the contents of the eye socket, including the eyeball, soft tissues, fat, and extraocular muscles responsible for eye movement. A primary feature of this bony shelf is the Infraorbital groove, a channel running along the Maxillary bone portion of the floor.
This groove continues forward into the Infraorbital canal, a pathway for neurovascular structures. The Infraorbital nerve, a branch of the Trigeminal nerve, and the Infraorbital artery pass through this canal. The nerve provides sensory function to the skin of the lower eyelid, cheek, side of the nose, upper lip, and gums.
Recognizing and Addressing Orbital Floor Injuries
Due to its relative thinness and location over the large Maxillary sinus, the orbital floor is the most frequent site of trauma known as an orbital blowout fracture. This injury typically results from blunt force trauma, such as a punch or a ball striking the eye. The force causes a sudden increase in pressure inside the eye socket, which is then transmitted to the weakest bony wall, causing it to fracture and displace downward into the Maxillary sinus.
Double vision (diplopia) is a common finding, frequently caused by the entrapment of the Inferior Rectus eye muscle within the fractured bone fragments. When this muscle is trapped, the eye cannot rotate correctly, particularly when attempting to look upward. Another sign is a sunken appearance of the eyeball (enophthalmos), which occurs when the fracture increases the volume of the eye socket, allowing the globe to settle further back.
The involvement of the Infraorbital nerve in the fracture site leads to numbness (hypoesthesia) in the areas it supplies, specifically the cheek, upper lip, and gums. Treatment for orbital floor fractures varies based on the severity. Small, non-displaced fractures may only require observation, a course of antibiotics to prevent sinus infection, and advice to avoid nose-blowing.
Surgical intervention becomes necessary if the double vision is persistent, if the muscle is clearly entrapped, or if the sunken eye appearance is significant. The goal of surgery is to release any trapped tissue and repair the bony defect, often by placing a synthetic implant or bone graft over the fracture site.