Abstract: Abstract:Objective  To locate the optic canal precisely by measuring related distances and angles between optic canal and certain landmarks. Methods 120 CT images from clinical database were chosen for measurement.The  line (L1) of the nasal bone tip (P1) and the middle point of tuberculum sellae (P2)  in centre sagittal plane were set as a baseline.The plane went through L1 and perpendicular to centre sagittal plane (L2) was set as measurement plane.The parameters were the medial canal wall length (D1),the distance between nasal bone tip (P1) and orbit end of optic canal (P3 ) (D2),the distance between P1 and cranium end of optic canal (P4) (D3),the distance between P3 and L2 (D4),the distance between P4 and L2 (D5),the angle between P1P3 and L2 (A1),and the angle between P1P4 and L2 (A2).Results  D1 was (10.51±1.07) mm on the left,(10.64±1.10) mm on the right,statistical difference was found 〖JP3〗between the two sides (P<0.05). D2 was (66.68±5.99) mm on the left,(66.81±〖JP〗5.97) mm on the right,there was no statistical difference between the two sides (P>0.05). D3 was (72.82±6.33)  mm on the left,(73.04±6.33)mm on the right,statistical difference was found between the two sides(P<0.05).D4 was (13.96±1.43) mm on the left,  (14.16±1.53) mm on the right,there was no statistical difference between the two sides (P>0.05). D5 was (6.65±1.25) mm on the left,(6.58±1.41) mm on the right,there was no statistical difference between the two sides (P>0.05). A1 was (12.26±1.63)°,and  A2 was (5.28±1.13)°.Conclusion  The parameters above can help to  locate the optic canal precisely in the measurement plane and provide reference for the decompression surgery.It also makes the surgery safer.

Key words: CT image, optic canal, location, decompression