NORMATIVE MEASUREMENTS OF ORBITAL STRUCTURES USING CT

OBJECTIVE. The purposes of this study were to establish criteria for t he diameters of normal extraocular muscles, to determine the normal po sition of the globe as revealed by CT, and to investigate the effects of age and sex on these structures. SUBJECTS AND METHODS. Diameters of extraocular muscles, distance from the interzygomatic line to the pos terior margin of the globe, width of the optic nerve-sheath complex, a nd length of the interzygomatic line were calculated for 200 normal or bits of 100 patients on axial and direct coronal CT images. Effects of age and sex on muscle diameters and globe position were analyzed. RES ULTS. Normal ranges for the diameters (mean +/- 2SDs) of extraocular m uscles were medial rectus, 3.3-5.0 mm; lateral rectus, 1.7-4.8 mm; inf erior rectus, 3.2-6.5 mm; and superior group, 3.2-6.1 mm. The normal p osition of the globe was 9.4 mm behind the interzygomatic line (range, 5.9-12.8 mm). The mean diameters of the extraocular muscles and the l ength of the interzygomatic line in male patients were significantly l arger than in female patients (p < .001). Statistically significant co rrelation was found between age and the diameters of the inferior and lateral rectus muscles (p = .32, p = .013; and r = .23, p = .048, resp ectively). CONCLUSION. Our results may be important in interpreting CT scans of the orbit because, to our knowledge, no reliable normative d ata exist regarding these orbital structures.