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

BACKGROUND: 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 medial 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. The mean diameter of the extra-ocular muscles of male 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 < 0.05). CONCLUSION: These normative values may serve as radiological reference values in the assessment of changes in size and suspected enlargement of the extraocular muscles in Nigerian patients. They may also be extrapolated to other Black African patients, until population studies become available.