Objective: To evaluate orbital pressure (OP), intraocular pressure (IOP), and the effectiveness of canthotomy, cantholysis, and septolysis using an experimental orbital hemorrhage model. Methods: Expired whole blood was injected into the retrobulbar space of 10 human cadaver orbits. At 1-mL increments, OP, IOP, and globe position were documented. The mean (SD) time interval between the injections was 84(36) seconds. Following injection of 22 mL, lateral canthotomy, cantholysis, and septolysis were performed. An additional 10 mL of blood was then injected. Results: After injecting 22 mL of whole blood, mean (SD) OP and IOP were 68.4 (32.2) and 71.5 (19.1) mm Hg, respectively. The OP and IOP correlated closely throughout the experiment, with a mean (SD) difference of 11.4(4.9) mm Hg (Pearson coefficient,0.97). Following canthotomy, cantholysis, and septolysis, there was a mean (SD) decrease of 48.0(27.2) mm Hg (70%) and 50.0(18.1) mm Hg (59%) in OP and IOP, respectively. With additional injection of 10 mL of blood, OP and IOP increased rapidly. Conclusions: The IOP and OP rose in direct proportion to the volume of whole blood injected; OP lagged behind IOP by 11mmHg, and surgical release of the orbit reduced OP by 70%. This effect was short-lived in the setting of continued simulated hemorrhage.
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