In order to be able to see the world around him, every human being has two eyes. But the eyes are part of a vast optical system composed of various elements that, by working together, allow us to see. In this optical system, there is the iris. This element is very important for the view.

1. Definition of the iris

The iris is a part of the optical system and, more precisely, the bulb of the eye. The iris is easily recognizable by its color, which varies from person to person.

In addition to the iris, the human eye is composed of many other structures: the cornea, the iridocorneal angle, the ciliary body, the lens, the sclera, the conjunctiva, the retina, the choroid, the vitreous and the eyelids.

The iris is one of the elements that allow a human being to see. It is located in the front of the eye, follows the choroid, and is located between the lens and the cornea. It is thanks to the small hole in the center of the iris that light can enter the eye. This opening is called the pupil. With the help of several muscles, the iris directly influences the pupil.

The iris is made up of several layers called the anterior layer, the stromal layer, the anterior epithelium, and the posterior epithelium.

2. Why is the iris not the same color in everyone?

Some people have blue eyes, and others have green or brown eyes. The color of the iris is not always the same because of the concentration of melanin in the iris. Melanin is a brown pigment found in the iris, but also in the hair or in the skin. The higher the concentration of melanin, the darker and browner the eyes. When the eyes are green, the concentration of melanin is average and when the eyes are blue, the melanin is in low quantity.

In some people, the color of the iris may not be the same from one eye to another. In fact, it is even possible for the iris of one eye to have several different colors, called heterochromia. A person can be affected by heterochromia from birth, but it can also be caused by a disease.

According to some studies, it seems that originally the first human beings all had brown eyes. But about 10,000 years ago, a genetic mutation would have made the eyes appear blue.

3. Why do almost all babies have blue eyes at birth?

It may sound strange, but most babies are born with blue eyes and then their irises change color to their final color. In reality, when a baby is born, the melanin in the iris is deep inside the eye, which is why the eyes are blue. As the weeks go by, the melanin will rise to the surface of the iris and the baby's eyes will become brown. If the melanin does not rise, the eyes will remain blue and if a low level of melanin rises to the surface, the baby's eyes will be green.

It is important to know that this phenomenon does not occur to everyone. In Asian or African babies, for example, the eyes are already dark from birth.

4. What is the purpose of the iris?

The main role of the iris is to allow the pupil to dilate or contract depending on the situation. The iris contracts the pupil with the sphincter muscle and dilates it with the dilator muscle. Thus, the iris controls the amount of light that enters the eye. When a person perceives a bright enough light, the iris in their eyes will instruct the pupils to contract so that less light enters the eyes. On the other hand, when a person perceives a dim light, the iris will instruct the pupil to dilate so that more light can enter the eye.

5. What are the diseases of the iris?

It is important to understand that eye diseases are not necessarily the same as those that can affect the iris. Here, we are only talking about pathologies affecting the iris itself and not the other structures of the human eye.

Thus, among the most frequent diseases that can affect the iris, we find iritis. This is an inflammation of the iris that is characterized by redness in the eye and pain. In addition, because of iritis, visual acuity can be reduced. Sometimes, iritis is accompanied by an inflammation of the ciliary body, which is called iridocyclitis.

Aniridia is another disease that affects the iris. In fact, it is a rare condition that affects one in 40,000 babies each year. Aniridia is a genetic malformation that affects children at birth or during childhood. This pathology is, quite simply, an absence of iris in the child who is affected. The amount of light that enters the eye is no longer controlled normally, which can be dangerous. If too much light enters the eye, it can cause damage to various structures in the eye. In addition, over time, aniridia can develop into glaucoma or cataracts.

Ocular albinism is also a disease of the iris. Specifically, it is a depigmentation of the iris and retina due to a low level of melanin. In the case of ocular albinism, the patient's iris is gray or blue in color, while the pupil has red highlights. In some cases, albinism also affects the skin and hair in addition to the iris, in which case it is called oculocutaneous albinism.

Finally, among the pathologies of the iris, we can also mention heterochromia. This is not a disease per se, but rather a physical characteristic that causes a difference in color in each iris. This is known as "vairish eyes".

6. How to treat iris diseases?

Unfortunately, there is no treatment for the different pathologies described above, which cannot be cured, except for iritis which is simply an inflammation that can be treated with medication. On the other hand, concerning aniridia, ocular albinism, and heterochromia, there is no way to cure these pathologies.

Aniridia and ocular albinism are the two most dangerous conditions, as they can worsen with prolonged exposure to sunlight or by looking at a bright light for too long. Aniridia can lead to glaucoma or cataracts, while albinism, if it also affects the skin and hair, can turn into skin cancer, among other things.

The World Health Organization (WHO) strongly recommends that people with aniridia or albinism wear sunglasses and cover their heads with a hat, but above all not go out in the sun. These recommendations are very important to avoid any risk of complications.

7. Which doctors specialize in iris?

There are no iris specialists as such, nor are there any specific medical examinations. Of course, there are many eye doctors, such as ophthalmologists, among others, but they are not necessarily able to read and understand the iris.

If the patient decides to undergo iridology (study of the iris), he or she can turn to an iridologist, a naturopath, or a homeopath. Iridology is often used in non-conventional medicine.

8. What are the medical examinations of the iris?

There are no real medical examinations of the iris since the main diseases of this structure of the eye cannot be cured. However, there is a technique used by some professionals that allows them to study the iris in order to obtain a complete health check-up of the patient. This technique is called iridology. Although there are no particular contraindications that prevent the use of iridology, no scientific study has been conducted to date to prove that this technique is really effective in making a concrete diagnosis of possible pathology.

Apart from that, we could mention biometrics (techniques for "measuring the living"). It is important to understand that each person is unique and that each iris is different. Thus, it is almost impossible to find two identical irises. Moreover, even in twins, the irises are not the same. Biometrics can, in some cases, succeed in identifying a person thanks to the recognition of his iris. Biometrics is often used in prisons, but also in customs services or in banks.

Sources :

Opticiens par conviction : qu’est-ce que l’iris : rôle et anatomie

Institut Laser Vision : qu’est-ce que l’iris ?

Pôle Vision : l’iris