Adaptability of Extraocular Muscle of Rabit in Experimental Exotropia

Kim, Seong Ju; Yoon, Kyung Chul; Park, Yeoung Geol

Abstract

Fusion loss or anomaly of eye muscle and its nerve is a cause of strabismus. This induces adaptation of vergence and muscle length, the mechanisms of which are normally responsible for long-term maintenance of ocular alignment and orthophorization. To determine variability of muscle length adaptation according to age, we divided white rabbits into three groups: Group I(less than 8 weeks of age and 15000gm of body weight), Group II(10~14 weeks and 1500~2000gm), GroupIII(more than 16 weeks and 2500gm). Under local anesthesia with intravenous pentobarbital sodium, the right eyeball was fixed in exotropic position by suturing through the periosteum of the lateral canthal region with 5-o polypropylene. The muscles of left eye were not operated and served as a control. We examined electron microscopically the changes in sarcomere of the experimental right medial rectus(RMR) and right lateral rectus(RLR) after sacrificing four rabbits of each group at 1, 2 and 4 weeks, respectively. Regardless of age, when the muscle(RLR) was immobilized in the lengthened position, sarcomeres were added on and its length decreased, and when the muscle(RMR) was immobilized in the shortened position, sarcomeres were lost and its length increased. In conclusion, the study revealed that experimental extraocular muscle of rabbit is adapted in the direction to produce maximal power of its muscle and maintain ocular alignment constantly.