Orbital and peri-orbital cellulitis reflect a spectrum of disease which are differentiated by the anatomy of the orbital septum.
Peri-orbital cellulitis refers to infection occurring anterior to the orbital septum (pre-septal) and orbital cellulitis refers to infection occurring posterior to the orbital septum (post-septal).
The orbital septum is a membranous sheet that forms the anterior boundary of the orbit and separates the pre-septal and post-septal spaces (Figure 1). The septum acts as a barrier to infection. It originates both superiorly and inferiorly from the orbital periosteum. Superiorly, it is continuous with levator palpebrae superioris. Inferiorly, it is continuous with the inferior tarsal plate.1
Orbital cellulitis involves infection of the muscle and fat within the orbit, posterior to the orbital septum.
It is more common in children, with the incidence reported to be 16-fold higher in children compared to adults.3
Differentiation between peri-orbital and orbital cellulitis can be difficult in the initial stages of infection.
Orbital cellulitis is a serious sight-threatening condition. Approximately 11% of patients will have visual loss following orbital cellulitis.4
Orbital cellulitis is commonly caused by a local spreading infection from acute bacterial sinusitis, typically from the paranasal sinuses.
Less common causes of orbital cellulitis include the extension of peri-orbital cellulitis, haematogenous spread, orbit trauma (e.g. dog bite), or contiguous spread from the face or teeth from recent surgery or dental infection.5
Typical symptoms of orbital cellulitis include:
Erythema and swelling around the eye
Painful eye movements
Change in colour vision
Other important areas to cover in the history include:
Past medical history: previous episodes of eye disease including any previous episodes of peri-orbital/orbital cellulitis
History of precipitating cause: for example orbital trauma, sinusitis, or dental infection
Duration of symptoms
Laterality (unilateral or bilateral)
Severity of symptoms (worsening, stable or improvement in symptoms since start)
In the context of suspected orbital cellulitis, the following clinical examinations should be performed:6
Oral cavity examination: assessing oral hygiene, any evidence of dental disease, and any recent dental treatment of the upper molars
Examination of the eyes and vision: including assessment of visual fields, visual acuity, colour vision, relevant afferent pupillary defect (RAPD), light reflexes, proptosis measurement of intraocular pressure and slit-lamp examination.
Altered colour vision *(red-green tends to be the first colours lost)
Bilateral eye signs may indicate cavernous sinus thrombosis. Nausea, vomiting, headache, neck stiffness may indicate intracranial involvement.
* The clinical findings marked with an asterisk are red flag features and should prompt clinicians to consider severe post-septal disease. These ‘grave eye signs’ are positive predictors of advanced disease, which includes abscess formation and cavernous sinus thrombosis.8
These patients will need cross-sectional imaging and multidisciplinary involvement.
Relevant laboratory investigations include:
Full blood count: may show elevated white cell count, particularly neutrophilia
C-reactive protein (CRP): may be elevated
Lactate: may be raised if the patient is septic
Blood cultures: the most common isolated organisms include Staphylococcus, Streptomyces species and Haemophilus
Microscopy, culture and sensitivity swabs: including swabs of the conjunctiva and nasopharynx
Contrast-enhanced CT orbit, sinuses and brain is the imaging modality of choice.
Imaging is required to assess for complications of orbital cellulitis (including abscess formation or intracranial involvement) and to guide ongoing management.
Imaging is indicated if clinical examination of the eye is not possible, there are any red flag eye signs, or there is a failure to improve (e.g. ongoing pyrexia) after 36-48 hours of intravenous antibiotics.9
MR venogram may be required to aid the diagnosis of cavernous sinus thrombosis. If meningeal signs develop, lumbar puncture is indicated. A CT head should be considered to exclude raised intracranial pressure prior to lumbar puncture.
Patients with suspected orbital cellulitis require emergency referral to ophthalmology and ENT.10
Patients with orbital cellulitis require intravenous antibiotics, for seven to ten days. Antibiotic choice depends on local guidelines and results from microbiological investigations.
The patient will require multidisciplinary care (ophthalmology, ENT and paediatrics) and re-imaging if necessary.
If an orbital collection is seen on imaging, evacuation of orbital pus or drainage of paranasal sinus pus may be required.
Chandler’s classification anatomically categorises orbital complications of acute rhinosinusitis (the most common cause of orbital cellulitis).
Although this is not a continuum of disease it is useful in diagnosis (especially as the difference in signs can be subtle). It also provides a useful aid in guiding management of peri-orbital and orbital cellulitis.11
Group 1: Pre-septal cellulitis (infection anterior to orbital septum)
Group 2: Orbital cellulitis (infection posterior to orbital septum)
Group 3: Subperiosteal abscess (pus collection between bone and periosteum)
Group 4: Intraorbital abscess (pus collection within the orbit)
Group 5: Cavernous sinus thrombosis (mural thrombus which may propagate centrally)
Broadly speaking, grade 1 can be treated medically with antibiotics. Grade 2 can also be treated medically however if there is no improvement surgical drainage should be considered. Grade 3 and 4 can be treated surgically (drainage endoscopically or externally). Grade 5 should be treated with anticoagulation as well as surgical drainage.
Complications of orbital cellulitis include:12
Cavernous sinus thrombosis
Loss of vision
Orbital cellulitis is a sight-threatening infection in the muscle and fat within the orbit, posterior to the orbital septum.
Orbital cellulitis is commonly caused by contiguous spread of paranasal sinusitis.
Clinical features include a painful red eye with proptosis, chemosis, painful eye movements, and decreased acuity.
Initial investigations include an endonasal swab and FBC, CRP, and lactate. Imaging may include CT orbit, sinuses and brain.
Medical management includes treatment with intravenous antibiotics, with surgery reserved for more complicated orbital cellulitis.
If not recognised and treated promptly there is a risk of visual loss, intracranial spread and rarely death.
Peri-orbital cellulitis (also called pre-septal cellulitis) is an infection in the eyelid tissues anterior to the orbital septum.
Peri-orbital cellulitis is a much more common and less serious than orbital cellulitis.13
Peri-orbital cellulitis is usually caused by superficial injury (e.g. insect bite, chalazion, conjunctivitis) or it can be secondary to upper respiratory tract infections or sinusitis.14
Typical symptoms of peri-orbital cellulitis include:
Pain, redness and swelling of the eyelid
Other important areas to cover in the history include:
A thorough clinical examination is required to exclude orbital cellulitis and red flag features. See the orbital cellulitis section for the examinations that should be performed.
Typical clinical features of peri-orbital cellulitis include:
Eyelid redness, mild tenderness and swelling
Unlike orbital cellulitis, patients with peri-orbital cellulitis are unlikely to experience significant pain.
Visual acuity and visual fields are normal, and there is no pain on eye movement. The patients colour vision will be intact and there will be no sign of chemosis or proptosis. A fever may or may not be present in peri-orbital cellulitis.
Patients with peri-orbital cellulitis are systemically well and symptoms are less severe. If there is severe eyelid swelling it may be difficult to rule out underlying orbital involvement and imaging may be required.
Table 1. Differentiating between orbital and peri-orbital cellulitis.
Painful and restricted
May be reduced
May be reduced
Yes, in severe cases
There are no specific investigations for peri-orbital cellulitis.
If there is any suspicion of orbital cellulitis or the diagnosis is unclear, referral to secondary care for further investigation is required (see orbital cellulitis section).
Consider emergency referral to ophthalmology/ENT if there is any suspicion of orbital cellulitis, the patient is systemically unwell, or not responding to treatment.
Paediatric patients should be urgently referred as they require empirical intravenous antibiotic treatment and daily review due to the difficulty in differentiating between orbital and peri-orbital cellulitis. Paediatric patients are often unable to give a history and can be challenging to examine.
For adult patients, oral co-amoxiclav is usually prescribed first-line (clindamycin if penicillin-allergic). Consider a follow-up review in 24-48 hours and safety netting advice should be provided to the patient.
As for orbital cellulitis, if a sinogenic cause is suspected then patients require intranasal treatment.
Peri-orbital cellulitis can spread to cause orbital cellulitis and its subsequent sequelae. As a result, it is important to provide adequate safety netting advice to patients with peri-orbital cellulitis.
Peri-orbital cellulitis is an infection anterior to the orbital septum. It is less severe than orbital cellulitis.
Peri-orbital cellulitis is usually caused by contiguous spread from facial or eyelid injury, a chalazion, insect bite, or conjunctivitis but can be caused by sinusitis.
The patient usually complains of a tender red, swollen eyelid. They are systemically well, have no eye signs but may have a fever.
If there is any uncertainty regarding the diagnosis or it is a paediatric patient, urgent referral to secondary care should be made. Otherwise, oral antibiotics can be used in the community with follow up in 1-2 days.
Peri-orbital cellulitis can spread and cause orbital cellulitis, so follow up of these patients in the community is necessary.
Peri-orbital and orbital cellulitis are dependent on whether the infection is anterior or posterior to the orbital septum.
Patients with either of these conditions may present with a red swollen, tender eye and a fever. Differentiating between orbital cellulitis (sight-threatening) and peri-orbital cellulitis (less severe) is challenging. If there is diagnostic uncertainty, early referral to ophthalmology/ENT for assessment and consideration of imaging is required.
Mr Rakesh Mistry
Dr Chris Jefferies
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