Anatomy
The Iris and Pupil: Your Eye's Light Regulator
The iris is the coloured ring visible at the front of the eye. It contains two sets of muscles that control the size of the pupil — the dark central opening — to regulate how much light enters the eye. The iris also gives each person their unique eye colour.
Anatomy Overview
The Iris and Pupil: Your Eye's Light Regulator
Structure & Components
Fixed or dilated pupil (iris sphincter paralysis — emergency)
Unequal pupil sizes (anisocoria) can indicate neurological issue
Iris colour changes can signal inflammation (uveitis)
Photophobia (light sensitivity) when iris cannot constrict properly
Rubeosis iridis — new blood vessels on iris in diabetic eye disease
Iris coloboma (congenital notch in the iris affecting light control)
Functions & Physiology
Two iris muscles: sphincter pupillae (constricts) and dilator pupillae (dilates)
Iris is controlled by the autonomic nervous system
Melanin pigment density determines eye colour (brown = more, blue = less)
Anterior chamber angle formed where iris meets cornea is critical for fluid drainage
Inflammation (uveitis) can cause the iris to stick to the lens (posterior synechiae)
Narrow-angle glaucoma occurs when iris blocks the drainage angle
Key Points
Dilating drops to examine the iris and inner eye during eye exams
Iris laser (iridotomy) to create drainage opening in narrow-angle glaucoma
Steroid drops for iris inflammation (uveitis)
Cosmetic iris implants (limited use, higher risk)
Tinted contact lenses to manage photophobia from iris defects
Pupilloplasty to reconstruct iris after trauma
Regular monitoring if anisocoria detected
Learn More About Eye Health
Understanding eye anatomy is the first step to protecting your vision. Our experts are here to answer any questions about eye health.
Book AppointmentAvailable 24/7
Still Have Questions?
Chat with KAISA 2.0, KSA's AI-powered assistant, for instant answers about eye health. Powered by ElevenLabs and backed by KSA's clinical knowledge base, KAISA is available 24/7 for consultations and guidance.