Mydriatics and Cycloplegics: NBEO Guide
Mydriatics dilate the pupil; cycloplegics also paralyze accommodation. Key drug classes, uses and board traps for NBEO and OKAP prep.
Which cycloplegic agent is commonly used for pediatric cycloplegic refraction?
Mydriatics and Cycloplegics in 30 Seconds
Mydriatics enlarge the pupil, while cycloplegics enlarge the pupil and paralyze accommodation by inhibiting ciliary muscle function. Mydriatics and cycloplegics support fundus examination, cycloplegic refraction, uveitis management and amblyopia treatment.
Mechanism by Drug Class
Anticholinergic agents, muscarinic antagonists: both mydriatic and cycloplegic
Tropicamide 0.5% to 1%: Onset 20 to 30 minutes, duration 4 to 6 hours, weak cycloplegia for fundus examination. Exam relevance: Fastest, shortest acting anticholinergic cycloplegic.
Cyclopentolate 1%: Onset 30 to 45 minutes, duration 6 to 24 hours, standard pediatric cycloplegic refraction agent. Exam relevance: First-line drug for routine cycloplegic refraction in children.
Atropine 1%: Requires days of dosing, produces the most complete cycloplegia and may last up to 2 weeks. Exam relevance: Choose for maximum cycloplegia, especially in young children or significant hyperopia.
Homatropine 2% to 5%: Intermediate duration of 1 to 3 days, commonly used for anterior uveitis. Exam relevance: Prevents posterior synechiae and relieves pain from ciliary spasm.
Scopolamine: Intermediate duration and cycloplegic effect broadly similar to homatropine. Exam relevance: Know it as a less commonly used intermediate-acting anticholinergic.
Sympathomimetic agent: mydriatic only, no cycloplegia
Phenylephrine 2.5% and 10%: Alpha-1 agonist that contracts the iris dilator muscle without paralyzing accommodation. Exam relevance: Combine with tropicamide for greater dilation, not cycloplegic refraction.
Phenylephrine 10% risk: Systemic absorption can cause hypertension, particularly in elderly patients and neonates. Exam relevance: Prefer 2.5% when systemic cardiovascular risk is a concern.
Key Clinical Uses
Fundus examination: Tropicamide, with or without phenylephrine, provides routine diagnostic dilation. Cycloplegic refraction: Cyclopentolate is standard, while atropine provides maximum cycloplegia when residual accommodation is suspected. Uveitis: Homatropine or atropine reduces ciliary spasm pain and prevents posterior synechiae. Amblyopia penalization: Atropine blurs the sound eye, encouraging visual use of the amblyopic eye. Angle closure risk: Check for a shallow anterior chamber or occludable angle before dilation. Pharmacologic mydriasis can precipitate acute angle closure in susceptible eyes.
4 Facts Exams Always Ask
Anticholinergic agents produce both mydriasis and cycloplegia by blocking muscarinic receptors on the iris sphincter and ciliary muscle; phenylephrine is mydriatic only via alpha-1 agonism. Tropicamide has the shortest duration and is used for routine fundus examination; cyclopentolate is standard for cycloplegic refraction in children. Phenylephrine 10% carries a risk of systemic hypertension particularly in elderly patients, neonates and cardiovascular disease. Anticholinergic mydriatics are relatively contraindicated in narrow or occludable angles because of acute angle closure risk.
The Classic Trap
Two traps recur on boards. First, using tropicamide for cycloplegic refraction in a child produces weak cycloplegia and can miss latent hyperopia, since only cyclopentolate or atropine provide adequate cycloplegia for pediatric refraction. Second, using phenylephrine 10% in an elderly or medically fragile patient risks systemic hypertension from alpha-1 mediated vasoconstriction, so the 2.5% concentration is preferred in these patients. In both cases, also confirm the angle is not narrow or occludable before dilating, since anticholinergic mydriatics can precipitate acute angle closure.
Clinical Pearl
The classic board combination for routine dilation is tropicamide plus phenylephrine, an anticholinergic paired with a sympathomimetic acting on different receptors for stronger dilation than either agent alone. For uveitis, longer acting cycloplegics such as homatropine or atropine prevent posterior synechiae and provide sustained relief from ciliary spasm pain. Atropine penalization, which blurs the sound eye to force use of the amblyopic eye, is a well established alternative to patching in amblyopia treatment.
Checkpoint 1
Phenylephrine should be used cautiously in patients with which systemic condition?
Checkpoint 2
Which cycloplegic is often used to relieve pain and prevent synechiae in anterior uveitis?
A 4 year old is scheduled for cycloplegic refraction to evaluate suspected hyperopia. The clinician must choose between tropicamide and cyclopentolate for adequate paralysis of accommodation. Which agent should be selected, and why does the alternative risk missing the true refractive error?
Which drug is a mydriatic but not a cycloplegic?
Sources & Publisher Info
AAO Basic and Clinical Science Course, Section 3: Clinical Optics. AAO Basic and Clinical Science Course, Section 6: Pediatric Ophthalmology and Strabismus. AAO EyeWiki: Mydriatics and Cycloplegics.
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