Learning Objective

Describe how autonomic nervous system drugs influence pupillary size and accommodation, focusing on muscarinic (M₃) stimulation and α₁-adrenergic agonists.

Muscarinic (M₃) Stimulation

Acts on the sphincter pupillae (circular muscle) and the ciliary muscle.

Effects:

1. Miosis (pupillary constriction)
2. Accommodation for near vision
   • The ciliary muscle contracts
   • The lens becomes more convex
   • Improves near focus

Clinical application:

• Used to treat closed-angle glaucoma → miosis opens the angle
• Example drugs: pilocarpine, carbachol

Activity

α₁-Adrenergic Agonists

Act on the radial (dilator) muscle of the iris.

Effects:

1. Mydriasis (pupil dilation)
2. NO cycloplegia
   • Ciliary muscle NOT affected
   • Accommodation remains intact

Clinical application:

• Used for mydriasis without affecting vision (e.g., fundoscopic exam)
• Example drugs: phenylephrine

Activity

Diagram: Effect of ANS Drugs on the Eye

Activity