Key Facts

Orbital cellulitis is an acute infection of the soft tissues posterior to the orbital septum. It must be distinguished from the far more common and less serious preseptal (periorbital) cellulitis, which involves tissues anterior to the septum. Orbital cellulitis is a sight-threatening and potentially life-threatening emergency.

Epidemiology

• Most common in children and young adults
• More common in winter months (correlates with sinusitis prevalence)
• Annual incidence approximately 1.6 per 100,000 in children
• More common in males
• Pre-existing sinusitis is present in >90% of cases

Aetiology

• Sinusitis (most common cause, particularly ethmoid sinusitis via paper-thin lamina papyracea)
• Periorbital trauma or foreign body
• Post-surgical (sinus or orbital surgery)
• Dental infection (upper molars/premolars)
• Dacryocystitis (lacrimal sac infection)
• Haematogenous spread from distant infection
• Common organisms: Streptococcus pneumoniae, Staphylococcus aureus, Streptococcus pyogenes, Haemophilus influenzae (children), anaerobes (Bacteroides, Peptostreptococcus), polymicrobial in many cases

Pathophysiology

• Infection spreads from sinuses to orbit via valveless ethmoidal veins or directly through thin orbital walls
• The lamina papyracea (medial orbital wall) is paper-thin and allows direct extension from ethmoid sinusitis
• Progressive stages: preseptal cellulitis → orbital cellulitis → subperiosteal abscess → orbital abscess → cavernous sinus thrombosis
• Raised intraorbital pressure compromises optic nerve blood supply and extraocular muscle function

Key Features

• Proptosis (eye pushed forward by retro-orbital swelling)
• Painful ophthalmoplegia (restricted and painful eye movements)
• Reduced visual acuity (optic nerve compromise)
• Periorbital swelling and erythema (often severe)
• Chemosis (conjunctival oedema)
• Fever and systemic illness
• Relative afferent pupillary defect (if optic nerve affected)

Red Flags

• Reduced visual acuity or colour vision (optic nerve compromise)
• RAPD (indicates optic neuropathy)
• Complete ophthalmoplegia
• Bilateral orbital cellulitis (suggests cavernous sinus thrombosis)
• Signs of meningism (headache, neck stiffness, photophobia)
• Deterioration despite 24-48 hours of IV antibiotics (abscess likely)
• Altered consciousness (intracranial complications)

Bedside

• Visual acuity (essential baseline, serial monitoring)
• Pupil examination (RAPD)
• Colour vision (red desaturation)
• Assessment of eye movements (painful restriction)
• Measurement of proptosis (Hertel exophthalmometer)
• Temperature and observations

Bloods

• FBC: raised WCC (neutrophilia)
• CRP/ESR: raised inflammatory markers
• Blood cultures (before antibiotics if possible)
• U&Es, LFTs: baseline

Imaging

• CT orbits and paranasal sinuses with contrast: investigation of choice
  • Identifies extent of orbital infection
  • Detects subperiosteal or orbital abscess
  • Demonstrates sinus disease
  • Ring-enhancing collection indicates abscess
• MRI orbits: superior soft tissue detail; better for intracranial complications
• CT with contrast venography: if cavernous sinus thrombosis suspected

Special Tests

• Microbiology: culture of any surgically drained abscess material
• Nasal swab may identify pathogen
• ENT assessment for concurrent sinusitis

Non-pharmacological

• Admission to hospital — all cases of orbital cellulitis require inpatient management
• Serial visual acuity monitoring (minimum 4-6 hourly)
• Head elevation to reduce orbital oedema
• ENT involvement for management of underlying sinusitis

Pharmacological

• IV antibiotics — start empirically, urgent:
  • IV co-amoxiclav 1.2g TDS (covers Gram-positives, Gram-negatives, anaerobes)
  • OR IV ceftriaxone 2g BD + IV metronidazole 500mg TDS
  • If MRSA suspected: add IV vancomycin (dosed per levels)
  • Duration: IV antibiotics until clinical improvement (typically 3-7 days), then switch to oral (total 2-3 weeks)
• Nasal decongestants and saline irrigation for associated sinusitis
• Analgesia: paracetamol and ibuprofen

Surgical

• Surgical drainage indicated for:
  • Subperiosteal or orbital abscess on CT
  • No improvement or deterioration after 24-48 hours of IV antibiotics
  • Declining visual acuity
  • Non-medial subperiosteal abscess (less likely to resolve with antibiotics alone)
• Endoscopic sinus surgery with drainage via medial orbital wall approach
• Functional endoscopic sinus surgery (FESS) for underlying sinusitis

Referral Criteria

• Emergency ophthalmology referral for all suspected orbital cellulitis
• ENT referral for sinus disease management
• Neurosurgery referral if intracranial complications (abscess, CST, meningitis)
• Paediatric referral if child affected

• With prompt treatment, >90% achieve full recovery
• Visual loss occurs in 3-11% of cases
• Intracranial complications (meningitis, brain abscess): <5% with prompt treatment
• Cavernous sinus thrombosis mortality: 20-30% historically; improving with modern treatment
• Subperiosteal abscess: medial abscesses in children <9 years may resolve with antibiotics alone in >75% of cases
• Recurrence risk is low with adequate treatment of underlying sinusitis
• Long-term sequelae: residual ophthalmoplegia, visual impairment, cosmetic deformity (rare)

Chandler Classification of Orbital Complications of Sinusitis

Distinguishing Orbital from Preseptal Cellulitis