Developmental adaptations in the extraocular muscles of Macaca nemestrina may reflect a predisposition to strabismus

Extraoclar muscle development has been studied in two species of monkeys (Macaca nemestrina and Macaca fascicularis). In these studies, the authors have demonstrated a distinctive developmental difference between the two macaques. Specifically, tubular aggregates (ordered aggregations of sarcoplasmic reticulum) occur transiently in the orbital singly innervated muscle fiber type in nemestrina extraocular muscles only. Tubular aggregates are typically seen in skeletal muscle fast-twitch fibers during neuromuscular disease or experimental denervation. The alterations in developing extraocular muscle either may be indicative of a primary muscle disorder or may be secondary to neurologic maldevelopment. The authors suggest that the presence of tubular aggregates in the extraocular muscles of nemestrina monkeys may be indicative of aberrant innervation levels during early postnatal development.