What is the role of the dilator iris muscle?

The dilator iris muscle is primarily responsible for the dilation of the pupil. When this muscle contracts, it pulls the iris outward, leading to an increase in the size of the pupil, allowing more light to enter the eye. This process occurs in response to low light conditions, enabling better vision in dim environments. Understanding this function is crucial, especially in contexts like pupil examination, where assessing the reaction of the iris muscles helps determine neurological function and eye health.

The other options pertain to different functions: constricting the pupil is managed by the sphincter muscle of the iris, controlling lens shape is done through the ciliary muscle, and tear production is regulated by the lacrimal glands, none of which relate to the role of the dilator muscle.