An ophthalmologist used a mydriatic for dilating the pupils to facilitate ophthalmoscopy. Which of the following is the shoest acting mydriatic?

Tropicamide: The time required to reach the maximal cycloplegic effect is usually 20-25 minutes, and the duration of this effect is only 15-20 minutes. It is an effective mydriatic with weak cycloplegic action and is therefore most useful for ophthalmoscopy. Cyclopentolate Hydrochloride: The onset of dilatation and cycloplegia is within 30-60 minutes. The duration of action is less than 24 hours. Homatropine: Maximal cycloplegic effect lasts for about 3 hours, but complete recovery time is about 36-48 hours. Atropine: The onset of action is within 30-40 minutes. A maximal effect is reached in about 2 hours. The effect lasts for up to 2 weeks. Ref: Flach A.J., Fraunfelder F.W. (2011). Chapter 22. Ophthalmic Therapeutics. In P. Riordan-Eva, E.T. Cunningham, Jr. (Eds), Vaughan & Asbury's General Ophthalmology, 18e.