Where is orbital cellulitis located relative to the orbital septum?

• A. Posterior to the orbital septum.
• B. Anterior to the orbital septum.
• C. Within the eyelid margin.
• D. In the conjunctival space.

Answer: (A)

The orbital septum acts as a barrier between the eyelid tissues and the orbit. Infections anterior to this barrier stay in the eyelids and surrounding soft tissues (preseptal cellulitis), while infections behind it involve the orbital contents itself (orbital cellulitis). Therefore, orbital cellulitis is located posterior to the orbital septum. Clinically, posterior involvement can bring eye movement pain, proptosis, restricted extraocular movements, and potential vision changes, whereas preseptal cellulitis typically lacks these orbital signs. Imaging with CT can help confirm whether the infection lies behind the septum and guide urgent management.