Which Cholinergic Antagonist is known for having the fastest onset of mydriasis?

Tropicamide is known for having the fastest onset of mydriasis among the cholinergic antagonists listed. This rapid action is particularly beneficial in clinical settings where quick pupil dilation is required for examination or procedural purposes.

Tropicamide achieves mydriasis within approximately 20 to 30 minutes after instillation, which is significantly faster than other options. The duration of action is relatively short, making it ideal for situations where prolonged dilation is not necessary.

In contrast, homatropine and cyclopentolate, while also effective at inducing mydriasis, have longer onset times compared to tropicamide. Scopolamine, primarily used for its effects on the central nervous system and for motion sickness, has a different profile and is not typically utilized for rapid pupil dilation. Thus, tropicamide stands out as the best choice for its swift action in inducing mydriasis.