Repeatability of the measurement of intraorbital optic nerve with CT

Objective To evaluate the repeatability and feasibility of the measurement of optic nerve sheath diameter (ONSD) and area (ONSA) in normal subjects using multi-slice spiral CT.Methods 64 slice spiral CT of brain was performed in 55 normal adults.The intraorbital ONSD and ONSA in axial sections,at 3,6,9,12 and 15 mm posterior to the globe,were measured using a standardized technique on the image workstation.The intraorbital ONSD and ONSA of all subjects were measured by a masked observer on 3 separate occasions.The intraclass correlation coefficient (ICC) and the within-subject coefficient of variation (CVw) were calculated to evaluate the repeatability of the measurement.Results In the measurement locations of 3,6,9,12 and 15 mm posterior to the globe,the ICC and CVw of the maximum of ONSD were 0.902 ～ 0.941 and 2.99％ ～4.50％,which of the minimum of ONSD were 0.902 ～ 0.943 and 3.54％ ～4.74％.The ICC and CVw of the ONSA were 0.932 ～ 0.957and 5.77％ ～ 7.37％,and the highest ICC value of the ONSA measurement at 3 mm posterior to the globe was 0.957.Conclusion The intraorbital ONSD and ONSA can be measured in normal subjects by 64 slice spiral CT with high repeatability.The measurement at 3 mm posterior to the globe shows the best reproducibility.This method is also useful for the diagnosis of contusion and inflammation of optic nerve. Key words: Nerve, optic;  Tomography, X-ray, computed;  Repeatability