The effects of steroid eye drops were tested on isolated preparations of the sphincter, dilator, and ciliary muscles of the monkey. The resting tension of sphincter and ciliary muscle strips decreased in the presence of the topical steroid preparations while that of the dilator muscle increased, and muscle contractions evoked by acetylcholine, epinephrine, serotonin, or potassium chloride were markedly inhibited. In all cases the steroids when tested without vehicles were ineffective while responses to the vehicles alone were identical to those of the steroid-containing eye drops. Some ingredients of the vehicles are capable of altering smooth muscle function in vitro possibly by disturbance of the permeability of the cell membrane.
Kern R, Macri FJ. Steroid Eye Drops and Their ComponentsEffect on Isolated Intraocular Muscles of Monkeys. Arch Ophthalmol. 1967;78(6):794-802. doi:10.1001/archopht.1967.00980030796018