Quantitative Assessment of Extraocular Rectus Muscle Using Dynamic Functional CT

Objective To measure the largest cross-section area of extraocular rectus muscle on primary position during the muscle contraction and relaxation states using CT. Materials and Methods Sixteen volunteers performed eyes CT scan at the extraocular rectus muscle contraction and relaxation states. The largest cross-section area,the normal range and functional degree of rectus muscle were measured on the coronary images using computer software. Results On primary position,the largest cross-section area and functional degree of the lateral rectus muscle were the largest among all the extraocular rectus muscles(F=4.204,P=0.021). There were no significant difference among the other rectus muscles (F=2.562,P=0.0087). Compared with the primary position,at contraction state,the largest cross-section area of medial rectus muscle increased by 35.7%,lateral rectus muscle increased by 49.4%,superior rectus muscle increased by 28.3% and the inferior rectus muscle increased by 27.4%,while at relaxation state,the largest cross-section area of the medial rectus muscle decreased by 29.6%,lateral rectus muscle decreased by30.7%,the superior rectus muscle decreased by 32.7%and the inferior rectus muscle decreased by 26.5%. Conclusion The normal range of the largest cross-section area of the rectus muscles may help us to make correct image diagnosis.