Pilocarpine causes:

Ans. A. Active miosisTwo types of muscle are present in the eyes. Circular muscle which have M3 receptor and radial muscle which have Alpha 1 receptor on them. When M3 is stimulated, it causes contraction of circular muscle leading to active miosis. When alpha 1 is stimulated, it causes contraction of radial muscle leading to active mydriasis. On the other hand, if M3 is blocked, it leads to passive mydriasis and blockade of alpha 1 receptor leads to passive miosis. Pilocarpine being cholinergic drug stimulates M3 receptor and thus causing active miosis.