What is the function of the orbicularis oculi muscle?

The orbicularis oculi muscle is primarily responsible for closing the eyelids. This muscle encircles the eye and is essential for protecting the eye from environmental damage, controlling light exposure, and facilitating the distribution of tears across the surface of the eye during blinking. The action of this muscle helps maintain moisture and provides comfort for the ocular surface.

Understanding the anatomy and function of the orbicularis oculi is important in veterinary ophthalmology, as issues with this muscle can lead to various ocular surface diseases or conditions. For example, weakness or paralysis of this muscle can result in incomplete eyelid closure, which may cause corneal dryness, irritation, or even ulceration.

The other options do not accurately describe the function of the orbicularis oculi muscle. The muscle does not open the eyelids; rather, this is the role of the levator palpebrae superioris. Elevating the third eyelid is primarily managed by different muscles such as the nictitating membrane retractor muscle. Lastly, tear drainage is controlled by the structures associated with the lacrimal apparatus, not the orbicularis oculi muscle.