Orbital compartment syndrome

Orbital compartment syndrome is an ophthalmological emergency referring to an increased intraorbital pressure that may lead to permanent visual impairment if left untreated.

Clinical presentation

Features usuallyFindings on exam may include:

• acutedecreased visual impairmentacuity ⁶
• periorbital bruisingglobe palpably tense and resistant to manual compression
• fixed, dilated pupil in the affected eyerestricted lid motion
• proptosis
• raised intra-ocular pressure
• the presence of ana relative afferent pupillary defect
• restricted extra-ocular muscle movement

The condition is often seen in the context of trauma so other signs of trauma, particularly craniofacial, are usually present as well.

Pathology

The orbit is a conical space formed by the rigid bony orbit as the apex and the eyelid and orbital septum as the base. The eyelid and septum however are also relatively rigid and movement of the eyelids is also restricted by the medial and lateral canthal ligaments. The orbital compartment is therefore unablesusceptible to dealan acute increase in pressure with large increasesan acute increase in intraorbital pressure.

Causesvolume. Potential aetiologies of increased intraorbitalan acute increase in orbital compartment pressure include:

• retrobulbar haemorrhage
  • blunt trauma (most commonly from trauma)common cause)
  • retrobulbar or peribulbar injections
  • metastases
• infection
• emphysema (tension pneumo-orbitus)
• post surgical
• contrast extravasation

Increased intraorbitalWhen the increase in orbital compartment pressure can quickly lead compression ofsufficiently diminishes the perfusion to the retina and optic nerve and (via the central retinal artery leading to ischaemia of the optic nerveand vasa nervorum, respectively) ischaemia and retinavision loss may occur.

Radiographic features

CT

Although the diagnosis of orbital compartment syndrome is a clinical one, CT may show:

• proptosis
• tenting of the globe - guitar pick sign
• stretching of the optic nerve
• tenting of the globe
  • may be defined by the presence of a posterior globe angle of less than 130 degrees
    • obtained by calculating the angle between medial and lateral tangential lines at the margin of the posterior globe which converge at the insertion of the optic nerve ⁶
  • the guitar pick sign refers to the resultant abnormally conical contour of the posterior globe 
• asymmetry/narrowing of the stretch angle
  • degree of discrepancy from contralateral eye may be correlated with diminished visual acuity ⁴
• retrobulbar haemorrhage
• associated orbital fractures, intracranial haemorrhage and other signs of trauma

Treatment and prognosis

Urgent decompression by performing a lateral canthotomy and cantholysis is required. Permanent visual damage can occur within one hour if the condition is left untreated.