Which of the following is NOT a function of the orbicularis oculi muscle?

The orbicularis oculi muscle is primarily responsible for functions related to the movement of the eyelids. It plays a crucial role in controlled blinking, which helps to keep the cornea moist and remove debris from the surface of the eye. Additionally, it protects the eye by closing the eyelids during reflex actions, such as when an object comes close to the eye, preventing potential injury. The muscle also assists in facilitating tear drainage through the puncta by promoting the movement of tears towards the nasolacrimal duct.

In this context, regulating pupil size is a function attributed to the iris, specifically controlled by the sphincter pupillae and dilator pupillae muscles. The orbicularis oculi does not have a direct role in altering pupil size, which is why this aspect is not considered one of its functions. Therefore, identifying the option related to pupil size as the correct choice highlights an understanding of the specific roles of various ocular muscles and structures.