What is Cycloplegia?
Cycloplegia is the paralysis of the ciliary muscle of the eye, resulting in loss of accommodation (the ability to focus on near objects) and allowing accurate measurement of refractive error, particularly in children. 1
Mechanism of Action
Cycloplegia occurs when anticholinergic medications block muscarinic acetylcholine receptors on the ciliary muscle, preventing its contraction and thereby eliminating the eye's ability to accommodate. 2, 1
- The ciliary muscle normally controls the shape of the lens to allow focusing at different distances 2
- When paralyzed, the lens assumes its flattest configuration, revealing the true refractive state of the eye without the confounding effect of accommodation 1
- This paralysis is accompanied by pupillary dilation (mydriasis) because the same anticholinergic agents also block the iris sphincter muscle 2, 1
Clinical Importance
Adequate cycloplegia is essential for accurate refraction in children because they have significantly greater accommodative tone compared to adults. 3
- Without cycloplegia, children's strong accommodation can mask hyperopia or falsely suggest myopia 3
- One study demonstrated that noncycloplegic refraction in school-aged children measured 0.65 diopters more myopic on average compared to cycloplegic refraction 3
- Accurate refractive error determination is critical for diagnosing and treating amblyopia and strabismus 3
Common Cycloplegic Agents
The most frequently used cycloplegic medications include:
- Cyclopentolate 1%: Produces rapid cycloplegia approximating atropine's effect but with shorter duration (maximal effect within 25-75 minutes, recovery in 6-24 hours) 3, 1
- Tropicamide 0.5-1%: Provides adequate dilation with even shorter duration than cyclopentolate, preferred when brief cycloplegia is desired 3, 4
- Atropine 1%: The gold standard providing maximal cycloplegia, but with prolonged effect lasting multiple days 3, 2
- Homatropine: A moderately long-acting agent used less frequently 5
Practical Considerations
The choice of cycloplegic agent depends on the patient's age, iris pigmentation, and clinical indication. 3
- For term infants over 12 months: cyclopentolate 1% is typically used 3
- For children under 6 months: combination of cyclopentolate 0.2% and phenylephrine 1% is preferred 3
- Heavily pigmented irides may require repeated doses or adjunctive agents like phenylephrine 2.5% or tropicamide 1% 3, 1
- Using topical anesthetic prior to cycloplegic drops reduces stinging and improves penetration 3
Side Effects
Uncommon systemic side effects of cycloplegic agents include: 3
- Fever, dry mouth, tachycardia
- Nausea, vomiting, flushing
- Somnolence
- Rarely, behavioral changes including delirium (particularly in children) 6
- Hypersensitivity reactions 3
Punctal occlusion during instillation reduces systemic absorption and minimizes these side effects. 3, 6
Important Contraindications
Cycloplegic agents can precipitate acute angle-closure glaucoma in patients with narrow iridocorneal angles. 6, 7