Objective:To evaluate the role of quantitative measurements of orbital medial wall in the morphology of blow-out fracture based on CT imaging. Methods:Patients with periocular trauma who underwent CT scan from January 2012 to December 2014 were reviewed. A hundred patients without orbital fracture and 76 patients with pure orbital fracture (50 medial orbital wall fracture patients and 26 inferior orbital wall fracture patients) were identified. Quantitative measurements of orbital medial wall including anterior height,posterior height,anteroposterior diameter,area of lamina papyracea and number of ethmoid air cell septa,lamina papyracea area/ethmoid air cell septa were compared between groups by independent t-test. Results:There were no significant differences in all measurements between bilateral sides in patients without orbital fractures(P > 0.05),as well as in the anterior height,posterior height,anteroposterior length,and area of lamina papyracea between patients with isolated medial fractures and those with isolated inferior fractures. The number of ethmoid air cell septa was significantly fewer (P=0.013) and lamina papyracea area/ethmoid air cell septa significantly larger (P=0.011) in patients with medial wall fractures compared to those with inferior wall fractures. Conclusion:No significant differences were found in quantitative measurements of orbital medial wall between bilateral sides. Under the similar external force,the patients with fewer ethmoid air cell septa and larger lamina papyracea area/ethmoid air cell septa might be more likely to develop a medial wall fracture in similar external force.