Normative Measurements of Ko rean Orbital Structure

ABSTRACT

We studied to establish criteria for the diameters of normal extraocular muscles, the width of the optic nerve, and the globe position by CT, and to investigate the effects of age and sex on these structures among Korean populations. Diameters of extraocular muscles, distance from the interzygomatic line to the posterior margin of the globe, width of the optic nervesheath complex, and length of the interzygomatic line were calculated for 428 normal orbit on axial and direct coronal CT images. Normal range for the diameters of extraocular muscles were medial rectus 2.2~5.4 mm, lateral rectus 2.1~4.9 mm, inferior rectus 2.5~5.7 mm, and superior complex group 2.6~6.4 mm. The mean optic nerve-sheath complex was 4.1 mm ranged from 2.9 mm to 5.3 mm, and the mean length of interzygomatic line was 103.8 mm. The normal position of the globe was 11.2 mm behind the interzygomatic line(range, 6.4~15.3 mm). The mean diameters of extraocular muscles, sum of all muscle, optic nerve-sheath complex, globe position, and the mean length of interzygomatic line were larger in males than females. However, there was no significant difference between male and female patients except interzygomatic line, and there was also no difference among the various age groups(P>0.05). Our results may help to assess enlargement of the extraocular muscles and the optic nerve as well as determining whether exophthalmos is present in a practical quantitative method.