**Core Concept**
Blowout fractures of the orbit occur due to blunt trauma, typically affecting the orbital floor or medial wall. The most common feature is a fracture of the orbital floor, leading to orbital contents herniation into the maxillary sinus and potentially causing diplopia, periorbital swelling, and enophthalmos.

**Why the Correct Answer is Right**
In a blowout fracture, force transmitted through the orbital floor causes a fracture of the thin orbital floor bone, particularly in the region of the maxillary sinus. This allows the globe and extraocular muscles to protrude into the pterygopalatine fossa, leading to visual disturbances and pain. The fracture of the floor of orbit is the hallmark of this injury, especially in high-impact trauma like a fall or motor vehicle accident.

**Why Each Wrong Option is Incorrect**
Option A: Deviation of septum is seen in nasal septal fractures, not orbital blowout injuries.
Option B: Retinal hemorrhage is associated with shaken baby syndrome, not orbital trauma.
Option C: Nasal bone fractures occur in nasal trauma, but are not specific to blowout fractures.

**Clinical Pearl / High-Yield Fact**
Blowout fractures most commonly affect the orbital floor, and patients often present with periorbital swelling, diplopia, and a "sunken" eye appearance. Early diagnosis with CT scan is essential to avoid complications like optic nerve compression or visual loss.

✓ Correct Answer: D. Fracture of floor of orbit