Objective: Establish criteria for the diameters of normal extraocular muscles using computerized tomography in a Thai population.

Material and Method: Diameters of extraocular muscles (medial, lateral, superior complex, and inferior rectus) were calculated for 200 patients on coronal direction of screening paranasal sinuses. The effects of age and sex were also analyzed

Result: Normal ranges for the diameters (mean ± 2 SDs) of extraocular muscles were 3.7±0.9 mm for medial rectus, 3.6±1.2 mm for lateral rectus, 4.0±1.4 mm for inferior rectus and 3.8±1.4 mm for the superior group. The mean diameter of the extraocular muscles in male patients was not significantly larger than in female patients (p>0.05). There was also no statistically significant correlation between age, diameter of each extramuscular muscle and the sum of all four muscles.

Conclusion: The present result may help radiologists and ophthalmologists to accurately assess enlargement of the extraocular muscles, particularly in Oriental populations.

Keywords: Extraocular muscle, Normal measurement, Computed tomography