Anticholinergic and a muscarinic receptor subtype M4-preferring antagonist
REVIEW Tropicamide binds to and blocks the receptors in the muscles of the eye (muscarinic receptor M4). Tropicamide acts by blocking the responses of the iris sphincter muscle to the iris and ciliary muscles to cholinergic stimulation, producing dilation of the pupil and paralysis of the ciliary muscle.
Manny RE, Hussein M, Scheiman M, Kurtz D, Niemann K, Zinzer K (July 2001). Tropicamide (1%): an effective cycloplegic agent for myopic children. Investigative Ophthalmology & Visual Science 42 (8): 1728-35. PMID 11431435.