Peri-orbital and orbital cellulitis are distinct clinical diseases, though have overlapping clinical features and therefore can be difficult to differentiate
- Orbital cellulitis: Infection within the orbit, (ie post-septal, the structures posterior to the orbital septum); Surgical emergency with major complications including loss of vision, abscess formation, venous sinus thrombosis and extension to intracranial infection with subdural empyema, and meningitis; & the majority (>80%) of cases relate to local sinus disease.
- Peri-orbital cellulitis: Infection of the eye lids and surrounding skin not involving the orbit (ie pre-septal, the structures anterior to the orbital septum)
- The globe is not involved in either infection.
The causative organisms, commonly bacterial but can also be polymicrobial, often including aerobic and anaerobic bacteria and even fungal or mycobacteria. The most common bacterial organisms causing orbital cellulitis are Staphylococcus aureus and Streptococci species. Rare cases of orbital cellulitis caused by non-spore-forming anaerobes Aeromonas hydrophila, Pseudomonas aeruginosa, and Eikenella corrodens have also been reported.
