What is the effect of atropine on intraocular pressure?

Effect of Atropine on Intraocular Pressure

Atropine should be avoided in patients with increased intraocular pressure or glaucoma, as it poses a risk of elevating IOP through pupillary dilation and potential angle closure, despite some evidence suggesting it may not significantly raise IOP in most myopic children. 1

Contraindication in Acute Settings

• The American Academy of Pediatrics explicitly states that ketamine (and by extension, anticholinergics like atropine) should be avoided in patients with increased IOP or increased intracranial pressure 1
• This contraindication is based on the mechanism that pupillary dilation from muscarinic antagonists is a predisposing factor for angle-closure glaucoma 2

Evidence from Myopia Treatment Studies

Safety Profile in Children

• A prospective study of 186 myopic children receiving various concentrations of atropine showed no significant IOP elevation with long-term use; in fact, both low- and high-cumulative atropine dosage groups experienced a smaller increase in IOP compared to untreated controls 3
• A larger retrospective review of 621 myopic children (ages 6-15 years) treated with atropine for up to 3 years found no statistical association between cumulative dose or duration of atropine therapy and risk of elevated IOP 2
• Neither the cumulative dose nor duration of atropine therapy correlated with IOP elevation risk in these pediatric myopia populations 2

Important Risk Factors

• Age and severity of myopia (more negative spherical equivalent) were positively associated with elevated IOP risk, independent of atropine use 2
• Older myopic children and those with more severe myopia require careful IOP monitoring regardless of atropine therapy 2

Case Reports of IOP Elevation

• A case report documented significant IOP elevation (36 mmHg OD, 32 mmHg OS) in a 9-year-old boy using 0.125% atropine eye drops combined with orthokeratology lenses; IOP normalized to 18/20 mmHg within 2 days of discontinuation 4
• This suggests that combination therapy with orthokeratology and atropine may carry higher risk than atropine alone 4

Mechanism Considerations

• Atropine causes pupillary dilation, which can precipitate angle closure in predisposed individuals 2
• The theoretical concern is that mydriasis may reduce aqueous outflow through the trabecular meshwork in susceptible eyes 1

Clinical Algorithm for Atropine Use

Pre-treatment Assessment:

• Measure baseline IOP in all patients before initiating atropine 4, 2
• Perform gonioscopy to assess angle anatomy in patients at risk for angle closure 1
• Identify high-risk patients: those with narrow angles, family history of glaucoma, or pre-existing elevated IOP 1, 2

Monitoring Protocol:

• Check IOP within 3-7 days after initiating atropine therapy, especially in children using concurrent orthokeratology 4
• Monitor IOP more frequently in older children and those with higher myopia (>-4.00 D) 2
• Discontinue atropine immediately if IOP rises above 21 mmHg or increases >5 mmHg from baseline 4

Contraindications:

• Absolute: Known angle-closure glaucoma, increased IOP, or increased intracranial pressure 1
• Relative: Narrow angles on gonioscopy, family history of angle-closure glaucoma 1

Common Pitfalls

• Assuming all anticholinergics are safe for IOP: While studies in myopic children show relative safety, this does not apply to patients with pre-existing glaucoma or anatomically narrow angles 1, 2
• Failing to monitor IOP in combination therapy: The risk appears higher when atropine is combined with orthokeratology lenses 4
• Ignoring age and refractive error as independent risk factors: Older children with higher myopia need closer IOP surveillance regardless of atropine use 2