Which eye drop is used as a dilating drop?

• A. Tropicamide
• B. Phenylephrine
• C. Ketorolac
• D. Proparacaine

Answer: (A)

Tropicamide is used as a dilating drop because it is a short-acting antimuscarinic that blocks muscarinic receptors on the iris sphincter muscle. This causes the sphincter to relax, allowing the pupil to dilate. It also produces mild cycloplegia, which can help during eye examinations by preventing accommodation. The onset is relatively quick (often within 15–30 minutes) and the dilation wears off in a few hours, making it ideal for routine dilated fundus exams with minimal downtime for the patient. By contrast, phenylephrine dilates mainly by stimulating the iris dilator muscle via alpha-1 receptors and can produce stronger dilation with more systemic effects and longer duration; the other drops are not used for dilation—ketorolac is an NSAID for inflammation/pain, and proparacaine is a local anesthetic.