Bleeding into the confined retrobulbar space causes an increase in volume and the globe to be displaced anteriorly leading to proptosis. This increase in volume causes a compartment syndrome of the orbital compartment, leading to increased tissue pressure which directly compresses the optic nerve and vascular supply to the nerve.
Retrobulbar hemorrhage should be assumed in any eye that is proptotic after midface trauma. Common signs and symptoms are decreasing visual acuity, pain, proptosis (tense hard eye), ophthalmoplegia, pale optic disc, and loss of direct light reflex.
Release has to be accomplished with in 90 minutes of injury for optimal visual salvage. Treatment should not be delayed for further investigation such as imaging. Lateral canthotomy with cantholysis is the surgical approach to treating retrobulbar hemorrhage. The last reference article has an excellent series of procedural pictures and a good description. Check out Roberts and Hedges as well. Surgical repair of catholysis is easily performed and poor outcomes are rare. Acetazolamide, hydrocortisone and mannitol all decrease retrobulbar pressure and are adjuncts to lateral canthotomy. These medications may be contraindicated in hypovolemic shock or head injury.
Winterton JV, Patel K, Mizen KD. Review of management options for a retrobulbar hemorrhage.mJ Oral Maxillofac Surg. 2007 Feb;65(2):296-9.
Perry M. Acute proptosis in trauma: retrobulbar hemorrhage or orbital compartment syndrome–does it really matter? J Oral Maxillofac Surg. 2008 Sep;66(9):1913-20.
Vassallo S, Hartstein M, Howard D, Stetz J. Traumatic retrobulbar hemorrhage: emergent decompression by lateral canthotomy and cantholysis. J Emerg Med. 2002 Apr;22(3):251-6.