Ct Study Of The Normal Orbit And Optic Canal Bone Diameters And Orbital Volume

Objective: To establish the measurement method of the normal orbital and optic canal by CT scanned, and to explore the clinical value of the orbital volume and its regressive equation. Method: 30 males and 30 females(120 normal orbits) respectively to separate into two groups. CT axial and coronal scanning were performed: on the coronal image which pass the lateral side of orbital, the diameters of left side to the right side and the superior side to the inferior side were measured. On the image of the nerve-optic plane(NOP) to survey the orbital depth, and the distance from the anterior margin of the lateral orbital side to the lateral margin of the superior orbital fissure and to the lateral side of the optic canal; The distance from the anterior margin mediaorbital side to the media margin of the optic canal, and to the superior orbital fissure. The width of the intraorbital opening and the intracranial opening of the optic canal, the length of medial and lateral wall of the optic canal. On the TPS(treatment planning system) workstation, the three-dimensional reconstructed of orbital, and got the orbital volume. The multiple linear regression equations of the orbital volume were induced by the SPLM 3.0 statistic software. Result: l)The located points of CT measurement and these diameters accorded with skull specimen incompletely. All diameters are nosignificant difference between left and right (P>0.05) , but the difference existed between male and female(P<0.01). 2)The diameters of the optic canal had high variation. They had statistic difference between the 2mm and 3mm thickness scanned (P<0.05).3)The orbital volume measured by the CT scanned. The average volume of men's were 24.70±1.21ml; The women's were 22.36 ± 0.50ml. The average error was 4.27% which compared to the anatomic measurement of specimens. The multiple linear regression equations were induced by the factors of the orbital diameters(the distances of orbital left side to the right, the superior to the inferior and the anterior to the posterior). The multiple correlation coefficient of male's was R=0.6225,and the female's was R=0.7965. The average error was 3.42% which between the predictive value by the equation and the measured by 3D images. Conclusion: The CT measurement of orbital and the optic canal is reliable and accurate, but it accorded with anatomic measurement incompletely. It is the first time to suggest that the orbital volume can be predicted by the multiple linear regression equation, and it offered the convenient and reliable method to measure adult orbital volume. It has clinical value for diagnosis of orbital malformation, and directed to orbit reconstruction and surgery of skull base.