## Distinguishing Orbital Cellulitis from Preseptal Cellulitis ### Key Discriminating Feature **Key Point:** Ophthalmoplegia (restriction of extraocular movements) and proptosis are the hallmark signs that distinguish orbital cellulitis from preseptal cellulitis. These indicate involvement of the orbital contents posterior to the orbital septum. ### Comparative Table | Feature | Orbital Cellulitis | Preseptal Cellulitis | |---------|-------------------|---------------------| | **Ophthalmoplegia** | Present (pathognomonic) | Absent | | **Proptosis** | Present | Absent | | **Chemosis** | Present | May be present | | **Eyelid edema** | Present | Present | | **Vision loss** | Common | Rare | | **Afferent pupillary defect** | May occur | Absent | | **Location** | Posterior to orbital septum | Anterior to orbital septum | ### Clinical Pearl **Clinical Pearl:** Ophthalmoplegia occurs because orbital cellulitis involves the extraocular muscles and/or cranial nerves (CN III, IV, VI) within the orbit. The presence of any restriction in eye movements—even subtle—is a red flag for orbital involvement and mandates urgent imaging (CT/MRI) and systemic antibiotics. ### High-Yield Mnemonic **Mnemonic:** ORBIT = Ophthalmoplegia, Restricted movements, Behind septum, In-orbit abscess, Toxic systemic signs ### Pathophysiologic Basis Preseptal cellulitis is confined to tissues anterior to the orbital septum (skin, subcutaneous tissue, orbicularis oculi muscle). Orbital cellulitis crosses the septum and involves: - Extraocular muscles (causing ophthalmoplegia) - Orbital fat and connective tissue - Cranial nerves within the orbit - Potential for cavernous sinus thrombosis **Warning:** Do not assume preseptal cellulitis is benign—it can progress to orbital cellulitis, especially if untreated or inadequately managed. 
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