Final answer:
Miosis, or pupillary constriction, is a potential symptom of overdose from opioids like heroin, fentanyl, and prescription pain relievers. Phenylephrine, in contrast, induces mydriasis and is used during eye exams. Pilocarpine can reverse the effects of phenylephrine, constricting the pupil and helping to treat glaucoma.
Step-by-step explanation:
Miosis, or pupillary constriction, can be a sign of overdose from a variety of substances including prescription pain relievers, heroin, fentanyl, and other opioids. These substances primarily activate the parasympathetic system, which leads to the constriction of the pupil. Substances that can cause miosis are often misused or taken in excessive quantities, potentially leading to serious health complications. For example, opioids such as oxycodone and methadone, when taken in high doses, can result in significant pupillary constriction.
In contrast to miotic agents, phenylephrine causes mydriasis, which is the dilation of the pupil by activating the sympathetic system. This reaction occurs when norepinephrine binds to adrenergic receptors in the radial fibers of the iris smooth muscle, and phenylephrine can mimic this action. Mydriasis induced by phenylephrine is often observed during eye examinations. However, pilocarpine, a muscarinic agonist, can reverse mydriasis by causing pupillary constriction and is used in the treatment of eye disorders such as glaucoma.