Iris and Pupil

Think of someone's eyes and it's not the retina

, optical nerve, or the macula that you remember, but the two parts of the eye that everyone sees the iris and the pupil. Eye color is a topic often discussed between new parents: Will she have blue eyes or brown, green or hazel? Focusing on the color of the eyes, we give little thought to what these parts of the eyes are actually contributing to our child's vision.

The Eye's Iris and Pupil Color and Beyond

Shaped like a flat donut or a slice of black olive, the iris identifies your eye color. The iris is a membrane that sits between the cornea and the lens. It contains a brown pigment called melanin and the more you have the darker your eyes will appear. If you have blue eyes, the melanin is located at the back of the iris and little where else, while brown-eyed people have lots of melanin scattered throughout the iris. Less common are those with pink eyes (albinos). Albinos have little or no pigment in their bodies, so the light reflects off the back of the eye where blood vessels are located, making the iris appear pink or red.

In rare instances, the one iris might be a different color than the other. This is known as "heterochromia irides" and is due to genetics. Additionally, one section of the iris can be a different color from the rest of the iris. This genetic abnormality is called "heterochromia iridum." Contact an eye doctor near you, if you have one of these conditions, it may be possible to cosmetically correct the abnormality with a colored contact lens.

The hole in the middle of the iris is called the pupil, and it allows light to pass through. Two sets of muscles control the size of the iris; one performs like a sphincter surrounding the pupil and the other is the dilator muscle that runs radially through the iris.

Two Interesting Iris Facts

Beyond color, the iris has other important functions. The iris controls the amount of light that enters the eye. Shine a light into someone's eye and you'll quickly see the iris retract to close down the amount of light the eye receives. The pupil becomes small because the eye is sensitive to abrupt changes in light.

Another little known fact about the iris is that it reacts to emotions. Look at something that is horrifying and your iris will constrict to shut down the light and image it receives. If you view something interesting, your iris will dilate to allow more light to pass.

Unique Characteristics of the Iris

Like your fingerprints, the iris is also unique to every person. With its individual color, unique texture and patterns, the iris acts as the personal biological signature of a person. Using camera technology, the identity of a person can be detected through the person's iris. This type of technology called iris recognition, has been commercially deployed for access entry.

Iris and Pupil

By: Sara Goldstein

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