Tropicamide

Tropicamide is a short acting antimuscarinic eye drop used to dilate the pupil for fundus examination and to give weak, brief cycloplegia. It is the first choice for routine diagnostic mydriasis because it works fast and wears off in hours.

Classification. Topical ocular antimuscarinic; mydriatic and weak cycloplegic.

Mechanism. Blocks muscarinic receptors on the iris sphincter and ciliary muscle, leaving the dilator muscle unopposed.

Pharmacodynamics. Mydriasis begins within 15 to 20 minutes, peaks at 20 to 40 minutes and lasts about 4 to 6 hours. Cycloplegia is weaker and shorter than with cyclopentolate and atropine and peaks at 20 to 35 minutes.

Pharmacokinetics. Systemic absorption through the nasolacrimal duct and conjunctiva is small but real in infants. Eliminated by hepatic metabolism and renal excretion.

Diagnostic mydriasis, adult and child. Tropicamide 0.5% or 1% eye drops, one drop in each eye; a second drop can be given 5 minutes later if dilation is inadequate. Examine 15 to 30 minutes after the first drop. Dark irides need 1%, and often an added alpha agonist.

Cycloplegic refraction, adult and older child. 1% one drop, repeated after 5 minutes; refraction after 30 minutes. Cycloplegia is partial; use cyclopentolate in children with strong accommodation.

Retinopathy of prematurity screening, preterm infants. Tropicamide 0.5% (or 0.25%) one drop in each eye, often with phenylephrine 2.5% or less, 30 to 60 minutes before examination. Use the lowest effective concentration and press the lacrimal sac to limit systemic absorption.

Maximum. Usually no more than two drops in each eye for a diagnostic visit.

Contraindications. Narrow anterior chamber angle or primary angle closure glaucoma; hypersensitivity.

Warnings. Can precipitate acute angle closure in predisposed eyes; assess the angle first where doubt exists. Rare systemic effects in children: dry mouth, tachycardia, flushing, behavioural change and, uncommonly, psychotic reactions, seizures or ataxia. Blurred vision and photophobia impair driving for 4 to 6 hours.

Adverse effects. Transient stinging, photophobia, blurred vision, rise in intraocular pressure; conjunctival allergy with repeated use.

Interactions. Additive effects with systemic antimuscarinics. Opposed by miotics.

Special groups.

• Pregnancy: acceptable for examination; use punctal pressure.

• Breastfeeding: compatible.

• Children and preterm infants: lower concentrations and punctal pressure; watch heart rate and feeding tolerance.

• Older adults: check anterior chamber angle; assess risk of angle closure.

• Kidney and liver impairment: no adjustment.

Formulations. Eye drops 0.5% and 1%; single use units where available.

Technique. Instil into the lower conjunctival sac and close the eye for 1 to 2 minutes with pressure over the lacrimal sac to reduce systemic absorption. Avoid contaminating the dropper.

Baseline. Anterior chamber depth (peripheral slit lamp assessment), intraocular pressure in at risk eyes, history of glaucoma.

Monitoring. Pupil size at the time of examination; intraocular pressure and symptoms of angle closure (pain, headache, haloes, vomiting) in the hours after dilation. Warn patients to seek urgent care if these appear.

Reversal. Allow wearing off. Dilute pilocarpine (0.5% to 1%) is sometimes used after examination in at risk older patients, but it does not fully reverse the effect and adds its own risks.