Table of Contents

Sympathomimetic eyedrops and their mechanism of action on the Iris

Sympathomimetic eyedrops and their mechanism of action on the Iris

Alpha-1 Adrenergic Agonists

cause vasoconstriction, mydriasis and uterine contractions
- Phenylepherine (neoynepherine): Alpha-1 receptor agonist
- Other similar drugs: Dipivefrin, naphazoline

Alpha-2 adrenergic agonists

have more effects on CNS
- Apraclonadine: weakly binds to Alpha-1 receptors
  - Will cause dilation in Horner syndrome pupil due to this binding effect and upregulation of the receptor that occurs 2-5 days after sympathetic block
- Bromonidine (Alphagan P) is similar with less Alpha-1 effect on pupil

Indirect Acting Agents

Cocaine: blocks reuptake of norepinephrine
- causes dilation in normal pupil but not in a Horner syndrome pupil
Amphetamine: causes release of and blocks reuptake of norepinepherine
- causes dilation in normal pupil but not in a Horner syndrome pupil.