Cycloplegics

Cycloplegics are drugs used in ophthalmology to block the action of the eye’s parasympathetic system on the ciliary muscle and iris sphincter, producing cycloplegia (paralysis of accommodation) and pupil dilation (mydriasis). They are employed to facilitate accurate refraction, fundus examination, and to manage certain inflammatory conditions of the eye.

Mechanism and overview

Cycloplegics act as antimuscarinic agents, mainly antagonizing M3 receptors in the iris and ciliary body. By inhibiting acetylcholine activity at these sites, they prevent accommodation and cause pupil dilation. They may also reduce ciliary muscle spasm and relieve pain in inflammatory conditions. Systemic absorption can yield anticholinergic effects beyond the eye, particularly in higher doses or with improper use.

Common agents and typical use

The main cycloplegics in clinical use include tropicamide (short-acting), cyclopentolate (intermediate), tropicamide often used for routine dilated exams in adults, cyclopentolate favored for pediatric refraction, and atropine (long-acting) or homatropine (intermediate) for longer-term cycloplegia when needed. Onset and duration vary: tropicamide typically begins within 15-30 minutes and lasts about 4-6 hours; cyclopentolate begins in 30-60 minutes and lasts around 24 hours; atropine can last several days to a week or more, especially in children.

Indications and cautions

Indications include facilitation of comprehensive dilated eye examinations, cycloplegic refraction in children, and adjunctive therapy in anterior uveitis or other inflammatory eye conditions. Contraindications include narrow-angle or angle-closure glaucoma, known hypersensitivity, and conditions where anticholinergic effects could be harmful. Caution is advised in young children, the elderly, or individuals with systemic anticholinergic sensitivity.

Adverse effects and safety

Local adverse effects may include stinging, conjunctival irritation, and photophobia. Systemic effects, though uncommon with topical use, can include dry mouth, flushing, tachycardia, restlessness or delirium in sensitive individuals. Careful dosing, minimizing systemic absorption, and monitoring in at-risk patients are essential.