Which type of agent is used to dilate the pupil?

Mydriatic agents are specifically designed to dilate the pupil, an action known as mydriasis. These agents work by inhibiting the muscles that constrict the pupil, allowing it to widen. This dilation can be necessary for various diagnostic procedures, such as examining the retina, or during surgery to provide better access and visibility for the veterinarian.

In contrast, other types of agents listed do not cause pupil dilation. Miotic agents actually constrict the pupil, astringents are used to shrink tissues and reduce secretions, and antiseptics serve to inhibit the growth of microorganisms. This makes the mydriatic agent the correct choice for the purpose of pupil dilation.