An ophthalmologist instils an eye drop that dilates the pupil fully, yet the patient's near vision and light-near dissociation of accommodation remain completely normal. The drug used is most likely:
- A Phenylephrine ✓
- B Homatropine
- C Atropine
- D Tropicamide
Correct answer: A. Phenylephrine
Explanation
Phenylephrine is an alpha-1 agonist acting on the radially oriented dilator pupillae muscle, producing pure mydriasis without touching the M3-mediated ciliary muscle, so accommodation is spared. All three antimuscarinics listed produce mydriasis together with cycloplegia by blocking ciliary muscarinic receptors, which would blur near vision. This separation of mydriasis from cycloplegia is the defining feature of sympathomimetic mydriatics.
Reference: Katzung's Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.