Orbicularis oculi muscle in children. Histologic and histochemical characteristics

This is the first study devoted to the histologic and histochemical characteristics of the orbicularis oculi muscle in children to the authors' knowledge. The orbicularis muscle was compared with extraocular, facial, and limb striated muscle. Light microscopy showed the orbicularis oculi muscle to be much smaller and more loosely packed than skeletal limb muscles. It further showed these muscle fibers to have greater variation in fiber size and shape and more endomysial and perimysial connective tissue. Finally, analysis of the histochemical reactions showed the orbicularis oculi had a higher percentage of fast-contracting fibers (Type II). This study establishes the histologic and histochemical standard characteristics for the orbicularis oculi muscle in children. It was found that orbicularis oculi muscles have some histologic and histochemical features in common with other facial muscles and other features in common with extraocular muscles.