Preseptal cellulitis is cellulitis involving the external soft tissues and eyelid.
The orbital septum, a connective tissue reflection of the periosteum, inserts into the eyelids and separates them from the orbits. Orbital inflammation is often caused by sinus infection because of the multiple venous channels that exists between the sinuses and orbits. Preseptal cellulitis must be differentiated from orbital cellulitis because orbital cellulitis has potential severe complications including orbital abscess, subperiosteal abscess, brain abscess, meningitis, optic neuritis, cavernous sinus thrombosis, and blindness. Preseptal cellulitis appears as inflammatory changes involving the external soft tissues. Intraconal - within the muscle cone formed by the rectus muscles.