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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Preseptal cellulitis is anterior to the orbital septum: eyelid erythema/swelling with normal vision, no proptosis, and full painless eye movements
- Orbital cellulitis is posterior to the septum: proptosis, painful/restricted extraocular movements, diplopia, decreased vision, RAPD, fever, or toxic appearance
- Orbital cellulitis is an emergency requiring hospital admission, CT/MRI orbit/sinuses, IV antibiotics, and ophthalmology/ENT involvement
- Most orbital cellulitis arises from bacterial sinusitis, especially ethmoid sinusitis
- Complications include subperiosteal abscess, cavernous sinus thrombosis, meningitis, brain abscess, and vision loss
Overview
Preseptal cellulitis is infection of eyelid and periorbital soft tissue anterior to the orbital septum. Orbital cellulitis involves tissues posterior to the orbital septum and can compromise the optic nerve, ocular motility, and intracranial structures. The distinction is high-yield because both can present with eyelid swelling and erythema, but orbital signs require urgent imaging, IV antibiotics, and specialist management.
Epidemiology
Preseptal cellulitis is more common and may follow local skin trauma, insect bite, hordeolum/chalazion, dacryocystitis, or spread from adjacent infection. Orbital cellulitis is less common but more dangerous and most often results from contiguous spread of bacterial sinusitis, particularly ethmoid sinusitis. Children are commonly affected, but adult disease can be severe, especially with diabetes, immunosuppression, dental infection, fungal sinusitis, or trauma.
Clinical Features
Symptoms
Preseptal: eyelid swelling, erythema, tenderness, and sometimes low-grade fever
Orbital: pain with eye movement or painful restricted eye movements
Diplopia from ophthalmoplegia suggests orbital involvement
Decreased vision, color desaturation, or visual field loss suggests optic nerve compromise
Headache, vomiting, altered mental status, or cranial neuropathies suggest intracranial extension
History of sinusitis, recent URI, dental infection, trauma, or surgery
Signs
Preseptal: eyelid erythema/edema with normal visual acuity, pupils, color vision, and extraocular movements
Orbital: proptosis
Orbital: ophthalmoplegia or pain with extraocular movements
Orbital: chemosis, fever, toxic appearance, or severe edema preventing eye opening
RAPD, decreased acuity, or impaired color vision suggests optic neuropathy
Cranial nerve III/IV/VI palsies or bilateral signs may suggest cavernous sinus thrombosis
Investigations
First-line
Visual acuity, pupils, color vision, and extraocular movementsCore bedside distinction. Any abnormality raises concern for orbital cellulitis or optic nerve compromise
External and slit-lamp examinationAssess eyelid, conjunctiva, cornea, anterior chamber, and signs of trauma or foreign body
Vital signs and systemic assessmentFever, toxicity, immunosuppression, or neurologic signs increase urgency
Second-line
CT orbit and sinuses with IV contrastIndicated for suspected orbital cellulitis, proptosis, painful/restricted EOM, decreased vision, severe swelling, trauma, abscess concern, or poor response
MRI orbit/brain ± MRVBetter for intracranial extension, cavernous sinus thrombosis, optic nerve involvement, or fungal disease concern
CBC, blood cultures, inflammatory markersUseful in febrile/toxic patients, admitted patients, or before IV antibiotics when feasible
Specialist
ENT evaluationNeeded for sinus source, subperiosteal abscess, orbital abscess, or need for drainage
Ophthalmology evaluationRequired for suspected orbital cellulitis and for any vision, pupil, motility, or pressure abnormality
1
Preseptal cellulitis — mild, reliable outpatient
- Oral antibiotics covering streptococci and Staphylococcus aureus; include MRSA coverage when local risk or purulence is present
- Common outpatient choices include amoxicillin-clavulanate plus MRSA coverage when needed, or clindamycin when appropriate
- Close follow-up within 24-48 hours; escalate if no improvement or orbital signs develop
- Children, immunocompromised patients, systemic toxicity, or unreliable follow-up may require admission
2
Orbital cellulitis
- Hospital admission with IV broad-spectrum antibiotics
- Empiric coverage commonly includes vancomycin plus a third-generation cephalosporin or ampicillin-sulbactam/piperacillin-tazobactam depending on severity and local patterns
- Add anaerobic coverage when dental infection, chronic sinus disease, or intracranial extension is suspected
- Urgent ophthalmology and ENT consultation
- Monitor vision, pupils, color vision, proptosis, EOM, and IOP frequently
3
Drainage and surgery
- Indications include orbital abscess, large or medial subperiosteal abscess with risk features, optic nerve compromise, intracranial extension, fungal infection, foreign body, or failure to improve on IV antibiotics
- ENT drainage of infected sinuses may be required for source control
4
Special concerns
- Diabetic or immunocompromised patient with sinus disease, black eschar, cranial neuropathy, or severe pain: consider invasive fungal infection such as mucormycosis
- Cavernous sinus thrombosis requires urgent imaging, IV antibiotics, and specialist management
Complications
- Optic neuropathy: Vision loss from compressive, ischemic, or inflammatory injury
- Subperiosteal/orbital abscess: May require surgical drainage
- Cavernous sinus thrombosis: Cranial neuropathies, bilateral orbital signs, sepsis
- Meningitis or brain abscess: Intracranial spread from sinus/orbital infection
- Exposure keratopathy: From severe proptosis or incomplete eyelid closure
- Fungal orbital infection: Rapidly fatal in immunocompromised or diabetic patients if missed
USMLE Step 2 CK Exam Tips
- 1Pain with eye movement + proptosis + fever = orbital cellulitis
- 2Preseptal cellulitis has normal visual acuity, no proptosis, and full painless extraocular movements
- 3Best next step for suspected orbital cellulitis = CT orbit/sinuses with IV contrast + IV antibiotics + admission
- 4Most common source of orbital cellulitis is ethmoid sinusitis
- 5Decreased vision or RAPD = optic nerve compromise, emergency
- 6Cavernous sinus thrombosis causes cranial nerve palsies and may become bilateral
- 7Diabetic patient with sinusitis and black nasal eschar = mucormycosis until proven otherwise
- 8Do not diagnose conjunctivitis when there is proptosis or painful restricted EOM
practicetest your knowledge on orbital cellulitis vs preseptal cellulitisApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — ophthalmology and beyond.
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