Tropicamid

Tropicamide is a short-acting antimuscarinic ophthalmic agent used to dilate the pupil and temporarily paralyze accommodation for eye examinations. It is commonly administered as topical eye drops, typically available in 0.5% or 1% solutions, and may be used alone or in combination with a sympathomimetic such as phenylephrine to achieve greater dilation.

Mechanism of action: Tropicamide blocks muscarinic acetylcholine receptors on the iris sphincter muscle and the ciliary body, causing relaxation of the pupil constrictor and accommodation muscles. This results in mydriasis (dilated pupil) and cycloplegia (loss of accommodation).

Onset and duration: Effects begin within about 15–30 minutes after instillation, with peak dilation occurring within 30–60 minutes. Pupil dilation generally lasts about 4–6 hours, while cycloplegia may persist longer, potentially up to 24 hours in some individuals.

Clinical use and administration: The primary use is to facilitate retinal examination, imaging, tonometry, and other diagnostic procedures. Dosing varies by concentration and clinical practice, but commonly involves one or two drops in each affected eye. In some regimens, tropicamide is paired with phenylephrine to enhance dilation, particularly in darker irides or when deeper dilation is desired.

Safety and contraindications: Tropicamide is usually well tolerated. Common local adverse effects include transient stinging, blurred vision, light sensitivity, and dry eye. Systemic anticholinergic effects are rare with topical use. Contraindications include known hypersensitivity to tropicamide or other muscarinic antagonists and conditions with narrow anterior chamber angle or risk of acute angle-closure glaucoma. Caution is advised in young children, the elderly, and patients with cardiac or central nervous system disease.