Cyclopentolate

Cyclopentolate is a topical antimuscarinic that gives rapid, strong cycloplegia and mydriasis. It is the usual agent for cycloplegic refraction in children, where accommodation hides hypermetropia.

Classification. Topical ocular antimuscarinic; cycloplegic and mydriatic.

Mechanism. Blocks muscarinic receptors on the ciliary muscle and iris sphincter, paralysing accommodation and dilating the pupil.

Pharmacodynamics. Mydriasis in 15 to 30 minutes; maximum cycloplegia at 30 to 60 minutes; recovery of accommodation in 6 to 24 hours, mydriasis may last up to 24 hours or longer in dark irides. Less prolonged than atropine, but longer than tropicamide.

Pharmacokinetics. Absorbed through the nasolacrimal mucosa; systemic exposure matters in infants and small children. Metabolised by esterases and excreted in urine.

Cycloplegic refraction, adult. Cyclopentolate 1% eye drops, one drop in each eye, repeated after 5 to 10 minutes; refract at 30 to 45 minutes after the last drop.

Cycloplegic refraction, children.

• Under 1 year, and lightly pigmented irides: 0.5%, one drop.

• Older children: 0.5% or 1%, one drop, repeated once after 5 to 10 minutes if needed. Darkly pigmented irides (common in East Africa) usually need 1% and sometimes a second drop; some centres add tropicamide.

• Do not use the 2% concentration in children.

Uveitis and diagnostic mydriasis. One drop of 0.5% or 1% two or three times daily for anterior uveitis when a short acting alternative to atropine is wanted; specialist use.

Maximum. Two drops in each eye in one visit; no repeated daily dosing in infants without specialist direction.

Contraindications. Primary angle closure glaucoma or a narrow anterior chamber angle; hypersensitivity.

Warnings. Central nervous system toxicity, mainly in children and older adults: confusion, disorientation, ataxia, incoherent speech, visual hallucinations, restlessness, psychosis, seizures. Higher sensitivity in children with Down syndrome, spastic paralysis or brain injury. In preterm and small infants, systemic absorption can cause feeding intolerance and, rarely, necrotising enterocolitis; use the lowest concentration and punctal pressure. Hyperthermia in hot weather.

Adverse effects. Stinging, burning, blurred vision, photophobia, raised intraocular pressure, tachycardia, dry mouth, flushing.

Interactions. Additive with systemic antimuscarinics. Reduces the effect of miotics and cholinesterase inhibitors.

Special groups.

• Pregnancy: acceptable for essential examination; use punctal pressure.

• Breastfeeding: compatible.

• Neonates and preterm infants: 0.5% or lower; watch for abdominal distension and feeding problems.

• Older adults: check the angle; higher risk of delirium.

• Kidney and liver impairment: no adjustment.

Formulations. Eye drops 0.5% and 1%; 2% is available in some markets but not advised in children.

Technique. Instil into the lower conjunctival sac, close the eyes for 1 to 2 minutes and press over the lacrimal sac. Wipe excess from the cheek. Do not allow infants to swallow drops from the face.

Baseline. Anterior chamber angle and intraocular pressure in at risk eyes; history of seizures or neurological disease.

Monitoring. Pupil and accommodation at the time of refraction; behaviour, gait and speech for 4 hours after in children; heart rate and feeding tolerance in infants.

Disposition. Warn the family about light sensitivity and blurred near vision for 24 hours; advise against driving and cycling until vision has recovered. Treat central toxicity by stopping the drug, giving supportive care and considering physostigmine only for severe cases under specialist direction.