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FIGURE 107.3 Mechanism of blowout fracture. In a sagittal view, a ball is shown striking the
eye, deforming it, and causing increased pressure of the intraorbital contents. The periorbital fat
is forced through the floor of the orbit. Retropositioning of the eye (enophthalmos), lowering of
the eye, and extraocular muscle entrapment can result.

In children, the floor of the orbit is relatively flexible. Consequently, it may
fracture in a linear pattern that snaps back to create a “trapdoor” fracture. In
adults, the floor of the orbit is thick and more likely to shatter when exposed to
force. If the inferior rectus muscle is entrapped in the fracture gap in the floor of
the orbit, voluntary upward gaze may be limited. Thin-cut coronal CT is
especially valuable in detection of orbital blowout fractures and extraocular
muscle entrapment. The presence of entrapment is an indication to operate on a
blowout fracture on an urgent basis.
A thorough ophthalmologic examination is warranted in all patients with
orbital fractures because of the high likelihood of associated eye injuries. In
particular, vision should be assessed because decreased visual acuity may be an
early sign of a retrobulbar hemorrhage, or injury to the optic nerve or eye itself. A
retrobulbar hemorrhage can cause compression of the central retinal artery, which
can threaten vision to the affected eye if not surgically decompressed. The type of
eye and orbit injuries varies on the basis of the object and mechanism involved.
Typically, a low-impact mechanism with a small object will result in injuries to