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