Which of the following drugs acting on dilator pupillae has an action analogous to that of pilocarpine on sphincter papillae?
Timolol
Epinephrine
Neostigmine
Tropicamide
Ans: B. Epinephrine(Ref Goodman Gilman 12/e p326,. Katzung, 13/e p162, 12/e p160,. KDT 7th/e p153. 6th/e p123).Epinephrine acts on dilator pupillae, causing the dilatation of pupil analogous to that of pilocarpine on sphincter papillae.Sympathetic stimulation of adrenergic receptors causes the contraction of the radial muscle and subsequent dilation of the pupil.Parasympathetic stimulation causes contraction of the circular muscle and constriction of the pupil.