Which Cholinergic Antagonist is indicated for the fastest onset of cycloplegia?

Cyclopentolate is known for its rapid onset of action, making it the best choice among the cholinergic antagonists for achieving cycloplegia quickly. When administered, it typically produces cycloplegia and mydriasis within 30 minutes, which is faster than other agents like atropine, homatropine, and tropicamide.

Atropine, while effective, has a slower onset and longer duration of action compared to cyclopentolate, which makes it less ideal when a rapid effect is needed. Homatropine also has a quicker response than atropine but does not match the onset speed of cyclopentolate. Tropicamide is known for its short duration and is commonly used in clinical practice for dilation; however, its onset is slightly slower than that of cyclopentolate.

In summary, cyclopentolate's formulation and pharmacokinetic properties facilitate a swift onset of cycloplegia, making it the preferred option when rapid pupil dilation and paralysis of accommodation are required.