An ophthalmologist needs to dilate a patient's pupil for fundus examination without causing loss of accommodation. Which drug achieves this?

• A Atropine
• B Homatropine
• C Tropicamide
• D Phenylephrine ✓

Explanation

Phenylephrine is a selective alpha-1 agonist acting on the dilator pupillae muscle, producing pure mydriasis without cycloplegia because the ciliary muscle lacks significant alpha-1 innervation. All the other options are antimuscarinics, which block M3 receptors on both the sphincter pupillae and the ciliary muscle, producing mydriasis together with cycloplegia and blurred near vision. When dilation without cycloplegia is needed, a direct alpha-1 agonist is the correct choice.

Reference: Katzung's Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.