Which substance is used to induce mydriasis in diagnostic procedures?

Tropicamide is a commonly used agent for inducing mydriasis, particularly in diagnostic procedures involving the examination of the retina and other internal structures of the eye. It is a fast-acting anticholinergic agent that works by blocking the action of acetylcholine on the sphincter muscle of the iris, resulting in pupil dilation. One of its significant advantages is that the mydriatic effect is relatively short-lived, which is beneficial for cases where quick recovery of normal pupil size is desired after diagnostic procedures.

While atropine is also an anticholinergic that produces mydriasis, it has a longer duration of action. Phenylephrine, although it induces mydriasis through a different mechanism (alpha-adrenergic agonism), is typically used in specific scenarios, such as when a neurogenic cause of miosis is suspected. Timolol is a non-selective beta-blocker primarily used to manage intraocular pressure in conditions like glaucoma and does not have mydriatic properties. Thus, tropicamide is the most appropriate choice for inducing mydriasis relevant to diagnostic examinations due to its rapid onset and short duration of action.