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Preseptal Cellulitis 1. Definition Preseptal cellulitis (also called periorbital cellulitis ) is an infection of the subcutaneous tissues anterior to the orbital septum , which includes the eyelid, periorbital skin, and subcutaneous tissues , but not the orbit itself. It must be distinguished clinically and radiologically from orbital cellulitis , which involves infection posterior to the orbital septum and carries a significantly higher risk of complications, including vision loss and intracranial spread. 2. Etiology and Causes 2.1. Etiologic Agents Preseptal cellulitis is usually caused by bacterial pathogens. The most common organisms include: Staphylococcus aureus (including MRSA) Streptococcus pyogenes (Group A Streptococcus) Streptococcus pneumoniae Haemophilus influenzae type B (Hib) – historically important, especially in children before widespread vaccination 2.2. Routes of Infection Contiguous spread from adjacent structures : Sinusitis (especially ethmo...