What medications cause pupil dilation?

Medications That Cause Pupil Dilation

Anticholinergic medications are the primary class of drugs that cause pupil dilation (mydriasis), with atropine being the most potent and longest-acting agent. 1

Mechanism of Pupil Dilation

Pupil dilation occurs through two primary mechanisms:

1. Anticholinergic action: Medications block muscarinic acetylcholine receptors in the iris sphincter muscle, preventing pupillary constriction
2. Sympathomimetic action: Medications stimulate alpha-adrenergic receptors in the iris dilator muscle, promoting pupillary dilation

Medications That Cause Pupil Dilation

Ophthalmic Medications

• Cycloplegic/mydriatic agents:
  • Atropine: Most potent, with effects lasting 7-14 days 2, 1
  • Scopolamine: Strong effect with duration of several days 3
  • Cyclopentolate: Moderate effect lasting 6-24 hours 4
  • Tropicamide: Shorter-acting with duration of 4-6 hours

Systemic Medications with Anticholinergic Effects

• Psychiatric medications:

  • Tricyclic antidepressants (TCAs) 5
  • Phenothiazines (antipsychotics) 6, 5
  • Some selective serotonin reuptake inhibitors (SSRIs) 5

• Other systemic medications:

  • Antihistamines (particularly first-generation) 6
  • Antiparkinsonian drugs (e.g., benztropine) 7
  • Antispasmodics (e.g., dicyclomine) 7
  • Certain motion sickness medications 8

• Recreational drugs:

  • Amphetamines 6
  • Cocaine 6
  • MDMA (ecstasy)
  • LSD

Clinical Implications of Pupil Dilation

Risk Factors for Complications

• Anatomical predisposition to angle closure:
  • Hyperopic eyes (farsighted) 8
  • Shallow anterior chambers 8
  • Narrow angles on gonioscopy 8
  • Family history of angle closure 8
  • Advanced age 8

Potential Complications

• Acute angle-closure glaucoma:

  • Medications with anticholinergic effects can precipitate angle closure in predisposed individuals 8, 7
  • Presents with severe eye pain, headache, blurred vision, halos around lights, nausea, and vomiting
  • Requires immediate treatment to prevent permanent vision loss

• Visual disturbances:

  • Photophobia (light sensitivity) 1
  • Blurred vision, especially for near objects (due to cycloplegia) 1
  • Difficulty with night driving

Special Considerations

Iris Pigmentation

• Darker irises may require higher doses of mydriatic agents to achieve dilation 2, 4
• Darker irises may retain anticholinergic agents longer, prolonging mydriatic effects 2

Age-Related Factors

• Children may be more sensitive to systemic effects of topical mydriatics 1
• Elderly patients may be more susceptible to adverse effects, including confusion and urinary retention 1

Prevention of Complications

1. Screen for risk factors before prescribing medications with anticholinergic effects
2. Warn patients about potential pupil dilation with certain medications 8
3. Educate patients about symptoms of angle closure that require immediate attention 8
4. Consider alternatives for patients with known narrow angles or history of angle closure 8
5. Apply digital pressure to lacrimal sac when administering ophthalmic anticholinergics to reduce systemic absorption 2

By understanding which medications cause pupil dilation and recognizing patients at risk for complications, clinicians can take appropriate precautions to prevent serious adverse events like acute angle-closure glaucoma while still providing necessary treatments.