Introduction

Orbital cellulitis is an inflammation of the soft tissues in the orbit of the eye posterior to the orbital septum.

Orbital cellulitis is caused by:

• Infection of the orbital soft tissues by extension of infection from periorbital structures (especially paranasal or ethmoid sinuses)
• Direct inoculation from accident, trauma or surgery
• Haematogenous spread.

Orbital infections are classified into five stages.  Although the classification does not necessarily imply an order of progression of disease, orbital abscesses are most often consequences of orbital cellulitis and preseptal cellulitis may cause intra-orbital infection.

Aetiology of orbital cellulitis

Pathogens are usually virulent organisms/strains, including:

• Staphylococcus aureus
• Streptococcus spp., including Streptococcus pneumoniae and beta-haemolytic Streptococcus spp. Group A
• Haemophilus influenzae
• Anaerobes
• Neisseria meningitidis
• Fungi, especially in the immunocompromised.

Diagnosis of orbital cellulitis

Clinical

Patients may be severely systemically ill with signs and symptoms including:

• Periorbital swelling
• Severe orbital pain
• Fever
• Conjunctivitis and chemosis
• Loss of colour vision
• Exophthalmos
• Impaired movement of the eye.

Microbiology

• Collect purulent material from the nose for Gram stain and culture on both aerobic and anaerobic media.
• Blood cultures:
  • Are often negative in adults
  • In younger children (<7–8 years of age) may reveal an organism, especially encapsulted organisms such as Streptococcus pneumoniae and Haemophilus influenzae which have a predilection towards bacteraemia in younger children (who have an IgG–2 antibody deficiency).

Imaging

A wide range of imaging techniques can be used:

• CT scan is the most useful investigation because it may reveal the presence and extent of any sub-periorbital abscesses
• MRI may be used to identify cavernous sinus thrombosis
• Ultrasound is less useful because it is poor at visualising posterior abscesses
• Plain x-rays are not normally useful
• Mucormycosis is rare, but if suspected, for instance in an immunocompromised patient, Hopkins rod with or without fibre optic nasopharyngeal endoscopy can be used to observe the characteristic black eschar formation which may be present.

Laboratory

• Complete blood count with differential.
  • Leucocytosis greater than 15,000 with a shift to the left is commonly seen.

Management of orbital cellulitis

Orbital cellulitis is a serious infection requiring rapid and effective treatment to preserve vision. The degree of visual loss from orbital cellulitis is related to the time taken to treat.

Rapid and effective treatment is required, including:

• High dose IV antibiotics
• Topical decongestants
• Surgery as appropriate:
  • If vision is affected (surgery is vital)
  • If the patient fails to improve on antibiotics
  If there is CT evidence of an orbital collection.

Suitable empirical antibiotic regimens on admission to hospital include:

• An injectable cephalosporin such as cefuroxime, plus metronidazole.

Penicillin-allergic patients:

• Clindamycin plus a quinolone such as ciprofloxacin. 

Treatment may be modified in consultation with an ophthalmic surgeon and your microbiologist.

Treatment may be refined based on microbiological findings and should be continued for 7–10 days.