Computed tomography measurement of extra-ocular muscle diameters in a population of normal patients in a tertiary hospital in Nigeria

Abstract

Measurements of extraocular muscle diameter may be useful in diagnosis and as an outcome indicator in the assessment of treatment options in thyroid-associated ophthalmopathy. Racial differences are known to account for craniofacial variations and orbital sizes. Objective: To determine the normal diameters of extra-ocular muscles using computed tomography in a homogeneous, group of hospital patients in a tertiary hospital in Nigeria. Material and Method: The maximum diameters of extra-ocular muscles were measured for 182 normal patients on thin slice reconstructed coronal computed tomography images. The effects of age and sex were determined. Result: Normal ranges for the diameters (mean + 2 SDs) of extraocular muscles were 4.5 + 1.2 mm for media l rectus, 4.9 + 2.1 mm for lateral rectus, 4.8 + 1.6 mm for inferior rectus and 4.0 + 1.5 mm for the superior group. T h e mean diameter of the extra-ocular muscles of mal e patients was not significantly larger than that of female patients (p > 0.05). There was a small but positive correlation between age and diameter of each extra-ocular muscle except in the left medial rectus and right lateral rectus muscles (P<0.005).