Optic Nerve Stretch in Orbital Compartment Syndrome

Abstract

Purpose:: Orbital Compartment Syndrome (OCS) can be the result of trauma and endogenous or postoperative bleeding. Once an orbital hemorrhage reaches a critical size, orbital compliance decreases, and intraorbital and intraocular pressures increase, potentially resulting in vision loss. During orbital compartment syndrome, the injury produced to the optic nerve is the result of a vascular insult and/or stretch, but the exact mechanism is uncertain. We surmise that evaluating the orbital commuted tomography (CT) in patients with clinical OCS may elucidate the incidence and impact of optic nerve stretching in these injurues. We also postulate that optic nerve stretch is a useful clinical finding in orbital trauma.

Methods:: We reviewed the charts and CT scans of 10 orbits (in 10 patients) with a clinical diagnosis of OCS, as defined by elevated intraocular pressure with "frozen globe" motility and an afferent pupillary defect. Using high resolution CT images, particular attention was directed to the optic nerve, which was digitally measured using a GE PACS^TM system. The optic nerve length was compared to the unaffected, opposite orbit. We reviewed the charts for mechanism of injury, visual acuity, intraocular pressure, and treatment rendered (e.g. canthotomy/cantholysis). Data from the initial evaluation and at final outcome were recorded.

Results:: The average optic nerve length was 35.68 mm in orbits with OCS. The average optic nerve length in the unaffected, opposite orbit was 28.08 mm. Six patients had statistically significant lengthening of the optic nerve on the affected side compared to the unaffected nerve. The final visual outcome in patients with "stretched" optic nerves was poor, but this was not statistically significant when compared to eyes without "stretching."

Conclusions:: Optic nerve stretch is seen in some, but not all cases of OCS. Digital measurement of the optic nerve length with comparison to the unaffected eye is quick and simple. The presence of statistical lengthening of the optic nerve (as defined by 20% increase over the opposite eye) may contribute in orbital trauma evaluation, especially in the setting of unobtainable (e.g. no intraocular pressure measuring device available) or unreliable (e.g. inexperienced examiner) clinical data.

Keywords: orbit • optic nerve • trauma