The anatomy of the muscle insertion (Scleromuscular junction) of the lateral and medial rectus muscle in humans

Purpose. To analyze the histologic features of the insertion of the medial and the lateral rectus muscles in humans. Methods. Postmortem study performed on 49 extraocular muscles from 21 subjects without known ocular disease. All muscles were obtained no longer than 8 hours after death, after consent for autopsy. Thirty-seven lateral recti muscles and 12 medial recti muscles were studied with light microscopy (hematoxylin-eosin and Goldner stains) as well as with enzyme histochemistry and immunohistochemistry, with monoclonal-human tenascin C antibody. Results. Light microscopic studies of muscle insertions of the lateral and the medial rectus muscle demonstrated muscle tissue connecting directly to the sclera without a tendon. These findings were confirmed immunohistochemically with tenascin C-antibody staining. Conclusions. Based on the results of this postmortem study in humans the term "muscle tendon" should be used with caution for the insertional area (scleromuscular junction) of the lateral and medial extraocular muscles. Light microscopy, histochemistry, and immunohistochemistry demonstrate that the tissue at the scleromuscular junction contains striated muscle with minimal connective (tendinous) tissue connecting to the sclera. To the best of the authors' knowledge, this is the first study in which enzyme histochemistry and immunohistochemistry have been used to investigate the anatomy of the insertional area (muscle-tendon-sclera junction) of the extraocular muscles in humans.