What structure separates preseptal and orbital cellulitis?

The structure that separates preseptal and orbital cellulitis is the orbital septum. The orbital septum is a fibrous membrane that acts as a barrier between the eyelids and the orbit. Preseptal cellulitis, which occurs in the eyelid and does not involve the orbit, is generally less severe and is usually caused by local infection, such as from a skin wound or conjunctivitis. In contrast, orbital cellulitis involves the orbital contents and can pose greater risks, including potential vision loss or other serious complications.

Since the orbital septum delineates these two areas, its presence is critical in clinical diagnosis. Any signs of proptosis, limited eye movement, or pain upon eye movement typically signal orbital cellulitis and indicate that the infection has spread beyond the confines of the eyelids into the orbit itself. Understanding this separation helps in assessing the patient's condition and determining the appropriate management and treatment strategies.