The Measurement of Size of Human Extraocular Muscles and their Changes in Thyroid Associated Ophthalmopathy in Korea

ABSTRACT

Enlargement of the extraocular muscles may cause diplopia and exophthalmos. The most common cause of the exophthalmos is thyroid associated ophthalmopathy(TAO), followed by inflammatory diseases and orbital tumors. TAO has the classical features of proptosis and lid retraction. However, the diagnosis is frequently confused with other eye diseases due to various symptoms and signs. Therefore, measurement of the size of extraocular muscles in both normal and TAO patients will make diagnosis and treatment plan easier in TAO and other muscular diseases of the orbit. For the clinical application, we measured the size of muscle with and without magnification and the results were compared. Normal mean values of cross sectional length and thickness of the extraocular muscles measured by CT scan showed 8.83x 3.60 in the inferior rectus, 9.20x3.20 in the superior muscle group, 9.45x 3.48 in the medial rectus and 9.65x3.23 mm in the lateral rectus muscle with no sex differences. All four muscles showed statistically significant enlargement in TAO and the thickness showed greater increase than the length. Superior muscle group(superior rectus and levator muscle)was the most frequently involved in TAO in both sexes. There was no significant statistical difference in the methods of measurement.