ABSTRACT
The dog has the highest incidence of eyelid disease due to the wide variation in conformation that has been bred into the species. The skin of the eyelids is typically thin and loosely adherent to the underlying tissue to facilitate movement. When making surgical incisions into the eyelid, the orbicularis oculi muscle is encountered immediately under the skin. The orbicularis oculi muscle is a superficial facial sphincter muscle and is the only muscle that contributes significantly to closure of the palpebral aperture. The orbicularis oculi muscle is involved in the efferent arm of the palpebral reflex, the corneal reflex, the glabellar reflex, the dazzle reflex and the menace response. The orbicularis oculi muscle is a strong muscle that is responsible for the severe blepharospasm seen with ocular pain. A vicious cycle of pain and blepharospasm occurs that, once it is well established in conformationally predisposed animals, is not relieved by removing the pain.
