Constrictor and Dialator Pupillae Muscle

Feature

Constrictor Pupillae Muscle

Dilator Pupillae Muscle

Function

Constricts the pupil (miosis) in response to light

Dilates the pupil (mydriasis) in response to low light or sympathetic stimulation

Innervation

Parasympathetic fibers from the oculomotor nerve (CN III)

Sympathetic fibers from the sympathetic nervous system

Control

Involuntary (reflex control)

Involuntary (sympathetic control)

Effect of Stimulation

Pupil constriction (miosis)

Pupil dilation (mydriasis)

Type of Muscle

Smooth muscle

Smooth muscle

Clinical Significance

Impaired function causes unresponsiveness to light

(e.g., in CN III palsy)

Damage causes miosis

(e.g., in Horner's syndrome)

Role in Pupillary Reflex

Acts as the effector in the pupillary light reflex

No direct role in the pupi