Iris: Anatomy, Function, and Iris-related Conditions

Published on February 16th, 2024

Updated on May 1st, 2025

The iris is the coloured part of the eye that controls the amount of light that enters the eye. The iris dilates and constricts the pupil which is called the pupillary light reflex. Eye problems that affect the iris include glaucoma, aniridia, uveitis, coloboma, pigment dispersion syndrome and Horner’s syndrome. The eye anatomy of the iris is made up of two zones, the ciliary zone and the pupillary zone. The iris is located in the centre of the eye, surrounding the pupil, under the cornea and on top of the lens.

What is the Iris?

The iris is located in the centre of the eye surrounding the pupil and is the coloured part of the eye. According to the National Eye Institute, the iris regulates the amount of light that enters the eye. The iris causes the pupil to dilate when it is dark which lets more light in and the reverse is true when in bright light, meaning the pupil constricts. Keep reading to learn more about what the iris is and how it helps the human eye see.

Are the Iris and Retina the Same Thing?

No, the iris and the retina are not the same thing, they are different parts of the eye’s anatomy. The retina is a layer of tissue located at the back of the eye that translates light into images. The iris regulates the amount of light that enters the eye by controlling the pupil. The iris and retina work together to help the human eye see.

What is the Structure of the Iris?

The structure of the iris is divided into two parts which are the pupillary zone and the ciliary zone. According to the Cleveland Clinic, the iris is made of nerves and muscles that control the size of the pupil. The iris is also filled with aqueous humour which it drains and produces to maintain the eye’s shape, pressure and size.

What is the Colour of the Iris?

The coloured part of a person’s eye is called the iris. This colour is unique meaning no two people have the same coloured iris. According to the Eye Doctors of Washington, irises are classified into six colours which are amber, blue, brown, grey, green and hazel. Eyes get their colour from the amount of melanin in your body. Melanin is a naturally occurring pigment that also gives your skin and hair colour, according to the Cleveland Clinic.

Where is the Iris Located in the Eye?

The iris is located in the centre of the eye, surrounding the pupil. According to the Cleveland Clinic, the iris location is under the cornea and on top of the lens, one layer from the outside of the eyeball.

What are the Two Regions of the Iris?

The two regions of the iris are the ciliary zone and the pupillary zone. The ciliary zone is larger than the pupillary zone and is adjacent to the ciliary body. The ciliary zone and the pupillary zone join at the collarette, which consists of nerves and blood vessels. The pupillary zone is located at the margin of the pupil, known as the pupillary ruff.

What is the Function of the Iris in the Eye?

The function of the iris in the eye is to control the pupil through dilation. The iris surrounds the pupil and causes it to dilate and constrict in response to light which determines how much light is let into the eye. This function is called the pupillary light reflex, according to the Cleveland Clinic. The iris also determines a person’s eye colour.

How Does the Iris Help the Human Eye See?

The iris helps the human eye see by controlling how much light the pupil lets in. The complete process for how the human eye sees is the cornea allows light to enter the eye, the iris adapts the pupil according to the intensity of light, the lens directs and concentrates the light onto the retina, the retina receives the light that is focused and the optic nerve carries visual information to the brain.

Does the Iris Help the Eyes See Colour?

No, the iris does not help the eyes see colour. While the iris is the coloured part of the eye, it does not affect the colours a person sees. The rods and cones in the eye are responsible for reacting to different colours of light and sending those signals to the brain via the optic nerve. The brain then translates what we see into something we can understand.

What are the Iris-related Eye Problems?

There are many eye conditions or problems that affect the iris. Iris-related eye problems include glaucoma, aniridia, uveitis, coloboma, pigment dispersion syndrome, synechiae, iridocyclitis and Horner’s syndrome. These eye conditions and their definitions are listed below.

Glaucoma: Certain types of glaucoma are iris-related problems that can lead to vision loss. Pigmentary glaucoma is characterised by the flaking off of the pigment in a person’s iris, which blocks fluid from draining out of the eye.
Aniridia: Aniridia is a rare genetic disorder characterised by the partial or complete lack of the iris. According to the Cedars Sinai Organisation, this condition causes symptoms of poor vision, strabismus, nystagmus and sensitivity to light.
Uveitis: Uveitis is characterised by inflammation of the eye and affects the iris, retina and choroid, among other parts of the eye. Uveitis can be categorised by where the inflammation occurs. Anterior uveitis develops in the iris which can cause pain, redness and blurry vision.
Coloboma: Coloboma is an eye condition that occurs when part of the tissue in the eye is missing. Coloboma can affect different parts of the eye including the iris, the lens and the macula. This eye condition is present at birth and can cause low vision and vision loss.
Pigment Dispersion Syndrome: Pigment dispersion syndrome occurs when the pigment rubs off the back of your iris which can cause a blockage in the eye’s drainage angle causing eye pressure problems, according to the American Academy of Ophthalmology.
Synechiae: Synechiae of the eye are abnormal adhesions between the iris and the lens and cornea. This eye condition causes the iris to stick to the clear tissue behind and in front of it. Synechiae can cause eye pain, vision loss and change in the shape of your iris or pupil.
Iridocyclitis: Iridocyclitis is inflammation of the iris and ciliary body and may be caused by an infection, an eye injury or for no apparent reason. Symptoms of this eye condition include eye pain, red eyes and sensitivity to light.
Horner’s Syndrome: Horner’s Syndrome is a rare eye condition that is caused by damage to part of the sympathetic nervous system, according to Very Well Health. Common symptoms of Horner Syndrome include a small pupil, partially drooping upper eyelid and loss of sweating on the face.

What are the Different Ways to Take Care of Your Iris?

The different ways to take care of your iris include having regular eye tests, wearing sunglasses for UV protection, following a healthy diet and staying hydrated. These actions for taking care of your iris are listed below.

Eye exams: Booking regular eye exams is very important for taking care of your overall eye health, including the iris. We recommend having an eye exam at least once every two years.
UV protection: UV protection in the form of sunglasses is extremely important as it can protect your eyes from the harmful rays emitted by the sun.
Healthy diet: A healthy and balanced diet benefits overall eye health, including the iris. A diet with omega-3 fats, leafy greens, nuts and seeds helps to protect the structures of the eye.
Stay hydrated: Staying hydrated by drinking plenty of water can help you take care of your eyes and iris. Dehydration can cause the eyes to become dry, red, blurry and cause problems focusing.

How Important is a Regular Eye Exam for the Iris?

A regular eye exam is very important for your overall eye health, including the health of your iris. In an eye test, an optometrist can assess your vision and eye health to determine if a patient has any eye conditions that require treatment or further assessment from an ophthalmologist. Eye tests performed to check the health of the iris include a light reflex test and pupillary observation. An optometrist’s diagnosis is crucial as early detection is often key in preventing vision loss.

How Can Oscar Wylee Help You Take Care of Your Eyes?

Oscar Wylee is equipped with skilled, in-store optometrists and modern technology to take care of our customer's eyes. We offer bulk billed eye tests for valid Medicare cardholders which assess your vision and eye health. With an Oscar Wylee eye test, we can monitor your eye for any changes and detect signs of eye diseases. Easily book an eye test online or in-store and take care of your eyes.

Can You Still See Without an Iris?

Yes, you can still see without an iris, however, your vision would be blurry. A person who is born without an iris or with part of their iris missing may have the condition called aniridia. According to Cedars Sinai Organisation, aniridia is a rare, genetic eye condition that may cause poor vision, nystagmus, strabismus and sensitivity to light. Aniridia can be treated with special glasses and surgery to replace the iris.

Does Wearing Eyeglasses Help Protect the Iris?

Yes, in some cases wearing eyeglasses, or more specifically safety glasses, can protect the iris from eye injury, acting as a barrier against environmental factors such as wind and dust as well as materials that may penetrate the eye. In general, wearing eyeglasses is done to correct a person’s vision if they have a refractive error.

What is the Difference Between the Iris and the Pupil?

The difference between the iris and the pupil is their appearance and anatomy. The iris is the coloured part of the eye and surrounds the pupil. The pupil is the black circle in the middle of the iris. The iris controls the pupil by dilating or constraining it to let light in.

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