Which medication, when overused, can cause pharmacologic mydriasis that mimics a third nerve palsy?

Which medication, when overused, can cause pharmacologic mydriasis that mimics a third nerve palsy?

• A. Tropicamide
• B. Scopolamine Patch
• C. Visine
• D. Pilocarpine

Answer: (C)

Pharmacologic mydriasis happens when a drug increases pupil size by stimulating the iris dilator muscle or by blocking the constrictor mechanism, so the pupil enlarges without nerve damage. Overuse of Visine, which contains tetrahydrozoline, a potent alpha-adrenergic agonist, can trigger this effect. By stimulating alpha receptors in the iris dilator, repeated use can produce a noticeably dilated pupil that may look like a third nerve palsy on exam — yet there’s no actual motor weakness or ptosis from nerve damage. This is the subtle but crucial clue: the dilation results from the drug’s action, not from a neuro-ophthalmic lesion, so recognizing the drug as the cause helps avoid misdiagnosis. Other options either cause dilation through different mechanisms less commonly abused (a clinic-administered mydriatic) or cause constriction (pilocarpine), so they don’t fit the scenario as well.

Pharmacologic mydriasis happens when a drug increases pupil size by stimulating the iris dilator muscle or by blocking the constrictor mechanism, so the pupil enlarges without nerve damage. Overuse of Visine, which contains tetrahydrozoline, a potent alpha-adrenergic agonist, can trigger this effect. By stimulating alpha receptors in the iris dilator, repeated use can produce a noticeably dilated pupil that may look like a third nerve palsy on exam — yet there’s no actual motor weakness or ptosis from nerve damage. This is the subtle but crucial clue: the dilation results from the drug’s action, not from a neuro-ophthalmic lesion, so recognizing the drug as the cause helps avoid misdiagnosis. Other options either cause dilation through different mechanisms less commonly abused (a clinic-administered mydriatic) or cause constriction (pilocarpine), so they don’t fit the scenario as well.