Orbital cellulitis is a serious infection of the bony cavity in which the eyeball sits. This cavity is called the orbit. It is surrounded by sinuses. The sinuses are the hollow areas of the skull around the nose.

Orbital cellulitis affects not only the eye, but also the eyelids, eyebrows, and cheeks. It causes the eyeball to have a swollen appearance. If the infection is not treated, it can lead to blindness.

Eyeball in Orbit
Eye bone socket nerve
The cavity below the eye is a sinus, the most common place for the infection to start.
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Orbital cellulitis is caused by certain bacteria.