Preseptal versus orbital cellulitis

The orbital septum is a fibrous barrier separating eyelid tissues from the deeper orbit. Preseptal cellulitis produces lid erythema, oedema and tenderness in front of this barrier. Orbital cellulitis involves structures behind it, including orbital fat and tissues around the extraocular muscles. Although the visible lid swelling can look similar, the consequences and treatment pathways differ substantially. The practical task is to establish whether ocular function is preserved and whether examination is reliable, not simply to grade how red the eyelid looks.

Preseptal infection may follow a skin wound, insect bite, hordeolum or nearby infection. Orbital disease commonly relates to sinus infection, especially in children, because of the anatomical relationship between the ethmoid sinuses and the medial orbital wall. Dental infection, trauma, surgery and spread from adjacent structures are other possibilities. Ask about preceding sinus or dental symptoms and recent injury, including a possible retained foreign body. A rapidly progressing or unusual presentation in an immunocompromised patient warrants early microbiology input and a broader differential.

A typical mild preseptal presentation has a tender swollen lid but normal acuity, pupils, eye position and painless full movements. Postseptal disease may cause pain on movement, restriction, diplopia, proptosis or globe displacement. Reduced colour vision, acuity or an afferent pupil defect indicates more serious visual pathway compromise. These features need not all be present. Early orbital infection can preserve acuity, and a distressed child may not describe diplopia. An inability to open the eyelids or complete the eye examination is a reason for a more cautious pathway.

Suspected orbital cellulitis requires hospital assessment, prompt intravenous antibiotics and coordinated ophthalmic and ENT care; paediatrics usually participates for children. Obtain blood cultures when indicated without delaying treatment. Contrast CT commonly assesses the orbits and sinuses, with brain imaging when complications are possible. The BSAC paediatric pathway also identifies inability to examine the eye, progression despite twenty-four hours of treatment or lack of improvement after forty-eight hours as imaging triggers. These are reassessment thresholds, not a reason to wait when an orbital sign is present initially.

Antimicrobial choice depends on age, local resistance, allergy, source and possible intracranial extension. For a selected adult with mild preseptal infection, NICE recommends co-amoxiclav 500/125 mg three times daily for seven days for infection near the eyes or nose, with specialist advice considered. One current Oxford adult orbital protocol uses ceftriaxone 2 g intravenously once daily with metronidazole 400 mg orally three times daily, for a total of seven to fourteen days and daily intravenous review. Suspected CNS infection requires a different specialist regimen; this example must not be extrapolated to infants.

Some patients need source control as well as antibiotics. An orbital or subperiosteal collection, compromised vision, substantial proptosis or failure to improve can lead to urgent drainage or sinus surgery. The decision depends on collection size and location, clinical findings and response, rather than an automatic rule that every small collection needs surgery. Conversely, a reassuring initial scan should not override subsequent visual deterioration. Serial eye and neurological observations are essential because the condition can change after the initial assessment.

Outpatient care is appropriate only for selected preseptal cases with a reliable normal eye assessment, adequate oral intake, manageable systemic state and dependable follow-up. Provide a clear review plan and immediate return instructions for visual symptoms, painful movements, severe headache or worsening illness. Children with significant swelling, fever or uncertainty need senior assessment; structured ambulatory intravenous care is a specialist service with its own safeguards. A prescription and an instruction to return at the end of the course are not sufficient for a patient whose disease extent remains uncertain.