Peri-orbital cellulitis is an infectious process occurring in the eyelid tissues superficial to (anterior to or above) the orbital septum. It is usually due to superficial tissue injury (e.g., insect bite or chalazion).
Orbital cellulitis is an infectious process affecting the muscles and fat within the orbit, posterior or deep to the orbital septum, not involving the globe. It is usually due to underlying bacterial sinusitis.
Peri-orbital cellulitis is of concern in children because it may be secondary to occult underlying bacterial sinusitis or, rarely, due to bacteraemic spread from a primary infection (e.g., pneumonia), and may rapidly progress to orbital cellulitis in children.
Complications include sub-periosteal abscess, cavernous sinus thrombosis, intracranial abscess, and subsequent loss of vision and/or death.