The orbital septum is a fibrous membrane running from the orbital rim periosteum to the tarsal plates, dividing the periorbital region into a preseptal (anterior) space and a postseptal (orbital) space. The preseptal space lies between the skin and the orbital septum; the orbital space lies between the orbital septum and the orbital fat. This distinction determines the classification and management of periorbital cellulitis.
| Location | Eyelids, in front of the orbital septum |
|---|---|
| Boundaries |
|
| Contents |
The orbital septum walls this space off from the orbit, so infection in front of it (preseptal cellulitis) is usually mild, while infection behind it (orbital cellulitis) threatens vision.
Preseptal (periorbital) cellulitis is infection confined to the preseptal space, typically from skin trauma, insect bites, or dacryocystitis, and presents with eyelid swelling and erythema without proptosis, restricted eye movement, or pain on eye movement. It is managed with oral antibiotics in mild cases and does not threaten vision. Orbital (postseptal) cellulitis from ethmoid sinusitis involves the orbital fat posterior to the septum, producing proptosis, chemosis, restricted painful eye movements, and potential vision loss from optic nerve compression; it requires IV antibiotics and often surgical drainage. CT with contrast confirms the orbital septum as the anatomical boundary.
The orbital septum is the critical anatomical boundary differentiating preseptal cellulitis (anterior, managed with antibiotics) from orbital cellulitis (postseptal, vision-threatening emergency requiring IV antibiotics and surgical drainage); CT confirms whether infection is anterior or posterior to the septum when the clinical examination is ambiguous.
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