An ophthalmologist needs to dilate the pupil of a 28-year-old man for fundus examination but wants to avoid loss of accommodation so the patient can read afterwards. Which drug produces mydriasis without cycloplegia?
- A Phenylephrine ✓
- B Atropine
- C Homatropine
- D Cyclopentolate
Correct answer: A. Phenylephrine
Explanation
Phenylephrine is a selective alpha-1 agonist that contracts the dilator pupillae muscle, producing mydriasis without affecting the circular sphincter or the ciliary muscle, so accommodation is spared. Atropine, homatropine and cyclopentolate are antimuscarinics that paralyse the sphincter pupillae and the ciliary body, causing both mydriasis and cycloplegia. This separation of mydriasis from cycloplegia based on receptor type is a standard examination point.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.