The orbicularis oculi muscle is one of the two major components that form the core of the eyelid, the other being the tarsal plate. The orbicularis oculi muscle is composed of skeletal muscle fibers, and receives nerves from the facial nerve. It is an important muscle in facial expression.
The orbicularis oculi muscle lies directly underneath the surface the skin, around the eyes. Its function is to close the eyelid, and to help in the passing and draining of tears through the punctum, canaliculi, and lacrimal sac, all parts of the tear drainage system.
The orbicularis oculi muscle is composed of three parts: the orbital portion, the palpebral portion, and the lacrimal portion. The orbital portion closes the eyelids firmly and is controlled by voluntary action. The palpebral portion closes the eyelids gently in involuntary or reflex blinking. The palpebral portion is divided into three parts; the pretarsal portion, the preseptal portion, and the ciliary portion. The lacrimal portion compresses the lacrimal sac, which receives tears from the lacrimal ducts and conveys them into the nasolacrimal duct.
Facial paralysis often affects the orbicularis oculi muscle. Inability to close the eye causes it to dry out, resulting in pain or even blindness in extreme cases.