Ocular Pharmacology

Mydriatics dilate the pupil by stimulating the iris dilator muscle (sympathomimetics) or blocking the iris sphincter (parasympatholytics). Phenylephrine 2.5% is the most commonly used sympathomimetic mydriatic — it dilates the pupil without affecting accommodation and is useful for fundus examination. Tropicamide 0.5-1% is a short-acting parasympatholytic that provides both mydriasis and cycloplegia (paralysis of accommodation), with onset in 20-30 minutes and recovery in 4-6 hours. Cyclopentolate 0.5-2% provides stronger cycloplegia for refraction in children, lasting 6-24 hours. Atropine 1% is the strongest cycloplegic with effects lasting 1-2 weeks, used primarily for pediatric refraction and amblyopia treatment. Always check for narrow angles before dilation — use the Van Herick technique or gonioscopy. Contraindications include narrow/closed angles and known hypersensitivity.