An ophthalmologist needs to dilate the pupil of a 28-year-old man for retinal examination but wants to avoid paralysis of accommodation so that near vision recovers quickly. Which drug best fits this requirement?
- A Atropine
- B Phenylephrine ✓
- C Homatropine
- D Cyclopentolate
Correct answer: B. Phenylephrine
Explanation
Phenylephrine is a selective alpha-1 agonist that contracts the dilator pupillae muscle, producing mydriasis without affecting the ciliary muscle, so accommodation remains intact. Atropine, homatropine and cyclopentolate are antimuscarinics that paralyse the sphincter pupillae and ciliary muscle together, giving mydriasis plus cycloplegia. The absence of cycloplegia is the defining discriminating feature of an alpha-1 sympathomimetic mydriatic.
Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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