From the Guidelines
To assess orbital compartment syndrome using ultrasound, position the patient upright and use a high-frequency linear transducer (7-15 MHz) with copious gel, looking for increased optic nerve sheath diameter, globe tenting, flattening of the posterior sclera, and decreased ocular blood flow on Doppler imaging. When evaluating orbital compartment syndrome, it is crucial to consider the clinical context and symptoms such as decreased visual acuity, pain, proptosis, and restricted eye movements 1. The American College of Radiology suggests that imaging analysis of orbital diseases is facilitated by a compartmental approach, establishing a differential diagnosis based on lesion location along the visual pathway 1. Some key features to assess in ultrasound include:
- Increased optic nerve sheath diameter (>5.0-5.9 mm is abnormal)
- Globe tenting (posterior displacement of the globe)
- Flattening of the posterior sclera
- Decreased ocular blood flow on Doppler imaging
- Ophthalmic artery resistive index, which increases with compartment pressure It is essential to compare findings with the contralateral eye when possible and correlate ultrasound findings with clinical symptoms. Ultrasound is a valuable tool in emergency situations due to its quick and non-invasive nature, but interpretation requires experience 1. Orbital compartment syndrome is an ophthalmologic emergency requiring prompt diagnosis and management, typically with lateral canthotomy and cantholysis if confirmed.
From the Research
Assessment of Orbital Compartment Syndrome in Ultrasound Scan
To assess orbital compartment syndrome in an ultrasound scan, several key features should be evaluated, as noted in the study by 2. These features include:
- Proptosis: The affected orbit is typically larger than the contralateral orbit, with a mean size of 24.4 mm compared to 17.7 mm.
- Optic nerve length: The optic nerve is often stretched, with a mean length of 32.0 mm compared to 25.8 mm in the unaffected orbit.
- Posterior globe angle: This angle is decreased, with a mean of 128.7° compared to 146.9° in the unaffected orbit.
- Morphology of the extraocular muscles: While there may be some variation, no significant differences were detected in the size and shape of extraocular muscles between affected and unaffected orbits.
- Superior ophthalmic vein caliber: In many cases (69%), the superior ophthalmic vein is smaller in the affected orbit.
Clinical Diagnosis and Imaging
It's essential to note that the diagnosis of orbital compartment syndrome is primarily clinical, as emphasized by 3 and 4. Imaging, including ultrasound, may be used to support the diagnosis but should not delay treatment. The clinical features and mechanisms resulting in orbital compartment syndrome, as well as its treatment and prognosis, are discussed in detail by 3 and 5.
Key Findings and Recommendations
The studies 2, 6, and 5 highlight the importance of immediate diagnosis and management to preserve vision in cases of orbital compartment syndrome. The emergency physician plays a critical role in this process, as outlined by 4. Key recommendations include:
- Early recognition of signs and symptoms
- Prompt intervention, including lateral canthotomy and inferior cantholysis if necessary
- Avoidance of delays in definitive surgical treatment
- Consideration of intervention even in cases of delayed presentation, as noted by 5