Preseptal & Orbital Cellulitis

The Critical Boundary: the Orbital Septum

Infections around the eye are classified by one anatomic landmark: the orbital septum — a fibrous sheet that runs from the orbital rim into the eyelids and walls off the eyelid soft tissue from the orbit itself. Infection in front of the septum (preseptal cellulitis) is usually managed with antibiotics alone. Infection behind the septum (orbital cellulitis) surrounds the eye, the extraocular muscles, and the optic nerve — and is treated as an emergency.

Preseptal Cellulitis

Preseptal cellulitis is an infection of the eyelid and periorbital soft tissue. It typically follows a skin source — an insect bite, stye (hordeolum), chalazion, trauma, or spread from the lacrimal sac (dacryocystitis) or sinuses. Common organisms include Staphylococcus aureus, Streptococcus pneumoniae, and (less often since routine immunization) Haemophilus influenzae.

• Signs: eyelid swelling, redness, warmth, and tenderness
• Crucially normal: vision, pupil reactions, eye movements, and globe position — the eye itself is quiet and comfortable

Older children and adults with mild preseptal infection are treated with oral antibiotics and close follow-up. Infants, the unimmunized, and any patient who worsens on oral therapy are admitted for intravenous antibiotics.

Orbital Cellulitis — an Emergency

Orbital cellulitis is infection of the tissues behind the septum. Roughly 90% of cases extend from bacterial sinusitis (especially the ethmoid sinuses, separated from the orbit by paper-thin bone); the remainder follow trauma, surgery, or spread from adjacent infection.

• Red-flag signs: pain with eye movement, restricted eye movements, proptosis (bulging of the eye), double vision, decreased vision, an afferent pupillary defect, and fever
• Feared complications: subperiosteal or orbital abscess, orbital apex syndrome, optic nerve compromise, and cavernous sinus thrombosis

Evaluation

Any suspicion of orbital involvement warrants CT of the orbits and sinuses — to confirm sinus disease, look for a subperiosteal or orbital abscess that would need surgical drainage, exclude a retained foreign body after trauma, and rule out a mass. Blood cultures are drawn before antibiotics. Vision, color vision, pupils, eye movements, and intraocular pressure are monitored serially — deterioration despite IV antibiotics suggests abscess formation.

Treatment

• Preseptal: oral antibiotics for mild adult/older-child cases; IV therapy for infants or progression.
• Orbital: admission and broad-spectrum intravenous antibiotics covering gram-positive cocci, H. influenzae, and anaerobes — typically 7–10 days IV followed by 10–14 days of oral therapy, with infectious-disease consultation as needed.
• Surgical drainage: for subperiosteal or orbital abscess, or failure to improve on IV antibiotics — often combined with endoscopic sinus drainage of the source.

An oculoplastic surgeon manages the orbital side of these infections — monitoring the optic nerve, draining abscesses, and coordinating care with ENT and infectious disease.