Proptosis and Orbital Disorders
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Direct answer
Proptosis (exophthalmos) is forward displacement of the globe, measured with the Hertel exophthalmometer, with readings above about 20 to 21 mm or a difference over 2 mm between the two eyes considered abnormal. Axial proptosis from lesions within the muscle cone (thyroid eye disease, cavernous haemangioma, optic nerve tumours) displaces the eye straight forward, while non-axial displacement indicates a lesion outside the cone, with the direction of displacement pointing opposite the lesion (for example, a superotemporal dermoid displaces the eye down and in). Orbital cellulitis, often from adjacent sinusitis, is the commonest inflammatory orbital presentation and a medical emergency; Chandler classification stages it from preseptal cellulitis through orbital cellulitis, subperiosteal and orbital abscess to cavernous sinus thrombosis. Evaluation combines the pattern of displacement, computed tomography or magnetic resonance imaging, and targeted management of the specific cause.
What you must remember
- Measurement: Hertel exophthalmometer readings with the normal adult value roughly 12 to 21 mm; asymmetry over 2 mm or absolute values over about 21 mm suggest proptosis; enophthalmos (posterior displacement) classically follows blowout fracture.
- Axial versus non-axial proptosis: axial points to intraconal lesions (thyroid orbitopathy, cavernous haemangioma, optic nerve glioma or meningioma); non-axial displacement localises the lesion to the opposite quadrant of the orbit.
- Pulsatile proptosis suggests a vascular communication (carotid-cavernous fistula, often with a bruit and conjunctival engorgement) or an orbital roof defect; intermittent proptosis with a varix; reducible proptosis in childhood haemangioma; painful proptosis in inflammatory disease (idiopathic orbital inflammation, formerly pseudotumour) or infection.
- Common causes by age: children: dermoid cyst, capillary haemangioma, rhabdomyosarcoma (the commonest primary malignant orbital tumour of childhood), optic nerve glioma, leukaemia and orbital cellulitis; adults: thyroid eye disease (the commonest cause overall), cavernous haemangioma (the commonest benign primary orbital tumour of adults), meningioma, lymphoma, mucocele and metastases (breast, lung, prostate).
- Orbital cellulitis: presents with painful proptosis, restricted and painful eye movements, chemosis, visual loss and fever, usually from ethmoid sinusitis; organisms include Staphylococcus aureus, Streptococcus species and, historically, Haemophilus influenzae in children; treatment is admission with intravenous antibiotics and CT of orbits and sinuses, with surgical drainage of abscess.
- Chandler classification of orbital infection: stage I preseptal cellulitis, stage II orbital cellulitis, stage III subperiosteal abscess, stage IV orbital abscess, stage V cavernous sinus thrombosis (with signs spreading to the contralateral eye, meningism and high fever).
- Differential of an acute "inflamed orbit": orbital cellulitis versus idiopathic orbital inflammation (pseudotumour, rapidly painful, responds dramatically to corticosteroids) versus thyroid eye disease; CT or MRI distinguishes these (celulitis with sinus opacification; pseudotumour with infiltrative enhancement and tendon involvement in myositis).
- Red-flag features needing urgent imaging and biopsy: rapid onset in childhood (rhabdomyosarcoma), bone destruction, painless progressive mass in an adult (lymphoma, metastasis) and vision-threatening compression requiring decompression.
Common confusion
The examiner's favourite distinctions are preseptal versus orbital cellulitis (preseptal: lid signs only with full motility, no proptosis and normal vision; orbital: proptosis, restriction, chemosis and possible visual loss, a sight and life-threatening emergency), and thyroid proptosis versus a true orbital mass. Students also forget that the direction of non-axial displacement points away from the lesion, which alone localises the mass. Another trap is calling every acute painful orbit "cellulitis" when idiopathic orbital inflammation responds to steroids and needs biopsy if atypical.
Exam-focused takeaway
Expect MCQs on the Hertel values and the over-2 mm asymmetry rule, the commonest tumours by age (rhabdomyosarcoma in children, cavernous haemangioma in adults, thyroid disease overall), Chandler stages, the sinus of origin (ethmoid), and the direction of displacement localising a lesion. The viva classic is differentiating orbital from preseptal cellulitis and stating management: intravenous antibiotics, imaging and abscess drainage, with ophthalmic artery or optic nerve compromise as the emergency indicator.
Frequently asked questions
How is proptosis measured and what is abnormal?
Proptosis is measured with the Hertel exophthalmometer, which records the corneal position relative to the lateral orbital rim in millimetres; normal readings average roughly 12 to 21 mm in adults. A difference of more than 2 mm between the two eyes or an absolute value above about 21 mm is abnormal and warrants imaging.
What causes axial versus non-axial proptosis?
Axial proptosis, with the globe pushed straight forward, indicates an intraconal lesion such as thyroid orbitopathy, cavernous haemangioma or optic nerve glioma. Non-axial displacement means an extraconal or wall lesion, and the globe is displaced away from it, so the direction of displacement points opposite to the lesion.
What is the Chandler classification of orbital infections?
Stage I is preseptal cellulitis; stage II is true orbital cellulitis; stage III is a subperiosteal abscess; stage IV is an orbital abscess; and stage V is cavernous sinus thrombosis, the most dangerous stage. Progression demands escalating therapy from intravenous antibiotics to surgical drainage.
Which tumours are commonest in the orbit in children and adults?
In children, dermoid cysts and capillary haemangiomas are common benign lesions, while rhabdomyosarcoma is the commonest primary malignant orbital tumour, presenting with rapidly progressive proptosis. In adults, cavernous haemangioma is the commonest benign primary tumour and lymphoma and metastases are the leading malignancies; overall, thyroid eye disease is the commonest cause of proptosis in adults.
How do preseptal and orbital cellulitis differ in management?
Preseptal cellulitis involves eyelid erythema and oedema anterior to the septum with normal vision, motility and no proptosis, and often responds to oral antibiotics. Orbital cellulitis adds proptosis, painful restricted movements, chemosis and visual risk, and requires admission, intravenous antibiotics, CT imaging of the orbits and sinuses and drainage of any abscess.