Iris of the eye: anatomy, function, influence on eye color & more

Did you know that the iris is not only responsible for your eye color, but also functions like personal sunglasses and high-tech shades for your eyes? This fascinating part of the eye plays a major role in regulating the incidence of light and protecting your vision.

But what is behind their complex anatomy? Why are no two iris colors the same? And what diseases can impair their function? In this blog, you will find out everything – from the function of the iris and its connection to the pupil to possible problems such as iridocyclitis or iris defects. Immerse yourself in the world of this colorful multi-talent and discover how the iris ensures clear vision and healthy eyes!

Anatomy and structure of the iris – the key to light regulation

The iris, also known as the iris, is a ring-shaped, colored area in the eye that lies between the cornea and the lens. It is part of the middle layer of the eyeball, known as the uvea, and plays a central role in regulating the amount of light entering the eye.

The iris consists of two main layers:

1. Stroma: This outer layer consists of connective tissue, blood vessels and pigment cells (melanocytes), which determine the individual eye color.
2. Pigment epithelium: A deeper, darker layer that absorbs light rays and thus reduces glare.

Embedded in the stroma are the iris muscles, which are responsible for the change in pupil size:

• The sphincter pupillae (ring muscle) contracts and causes the pupil to constrict in bright light.
• The dilator pupillae (ray muscle) opens the pupil to let in more light in the dark.

The iris separates the anterior chamber of the eye from the posterior chamber. These chambers contain the aqueous humor, which supports the health of the iris and the entire eye.

The pigmentation of the iris also protects the eye from harmful UV radiation by absorbing reflected light. This protective mechanism is particularly important for eye health and prevents excessive strain on the sensitive eye.

Together with the pupil, the iris functions like a diaphragm that regulates the amount of incoming light and thus creates the basis for optimal vision.

Function of the iris in the eye: How does the eye work?

The iris plays a crucial role in the functioning of the eye by regulating the incidence of light and thus enabling clear vision. It works closely with the pupil, the lens and the retina.

Regulating the amount of light – the function of a shutter

The iris acts like a diaphragm that controls the size of the pupil and thus regulatesthe amount of incoming light.

• In bright light, the circular muscle of the iris contracts, causing the pupil to become smaller and less light to enter the eye.
• In the dark, the iris relaxes and the ray muscle opens the pupil to let in more light.

This adaptability protects the eye from glare and ensures that the optimum amount of light always reaches the retina, where the actual image is formed.

Focusing and forwarding light beams

The iris not only regulates the amount of light, but also helps to direct the rays of light so that they ideally hit the macula lutea (the area of sharpest vision) in the retina. This enables clear and sharp vision in different lighting conditions.

Interaction with other parts of the eye

The regulated amount of light then passes through the lens, which concentrates the rays and focuses them on the retina. There, the light is converted into electrical nerve impulses by photoreceptors and transmitted to the brain via the optic nerve. Without the regulation of light incidence through the iris, clear perception would be impossible.

The function of the iris is therefore crucial for adapting to changing light conditions and for creating an accurate image. It protects the eye from being overloaded by too much light and ensures optimal use of vision.

Influence of the iris on eye color explained

A person’s eye color is largely determined by the iris, or more precisely by its pigmentation. This pigmentation is created by the quantity and distribution of melanocytes (pigment cells) in the iris, which, together with the structure of the iris, is responsible for the individual eye color.

What does the color of the iris depend on?

The color of the iris is influenced by three factors:

1. Amount of pigment:
   • A lot of pigment leads to brown eyes.
   • Little pigment results in green or blue eyes.
2. Distribution and density of pigment cells in the stroma:
   • Different arrangements of pigment cells in the stroma (outer layer of the iris) influence the scattering of light.
3. Reflected light:
   • Blue eyes are caused by the scattering of light in a weakly pigmented iris. This phenomenon is similar to the scattering of sky light and does not depend on blue color in the pigment.

Why is eye color individual?

Individual eye color is determined by genetic factors. Several genes influence the amount and distribution of pigments. These variations explain why no two iris colors are exactly the same. Even small changes in pigmentation can produce a unique coloration.

Special cases of eye color

• Albinism: In this genetic disorder, the pigment in the iris is almost completely absent. As a result, the eyes appear reddish as the light reflects off the blood vessels in the eye.
• Heterochromia: Different eye colors in one or both eyes are caused by unevenly distributed pigments.

Changes in eye color in the course of life

The color of the iris can change slightly over time. In babies, the final eye color often only becomes visible after a few months, when pigment production is complete. Pigments can fade with age, making the eye color appear lighter.

Disease of the iris as part of the eye at a glance:

The iris can also be affected by diseases. In contrast to healthy eyes, this can lead to impaired vision. The three most common diseases of the iris are

Iridocyclitis – inflammation of the iris

Iridocyclitis is an inflammation of the iris (iris) and the adjacent ciliary body, an important part of the eye. It is one of the forms of uveitis and can occur acutely or chronically.

Causes:

• Autoimmune diseases such as rheumatoid arthritis or ankylosing spondylitis.
• Infections caused by bacteria, viruses or parasites.
• Trauma or complications after eye surgery.

Symptoms:

• Pain in the eye and sensitivity to light.
• Redness around the iris.
• Blurred vision and increased sensitivity to glare.

Treatment:

• Corticosteroids (drops or injections) to reduce inflammation.
• Mydriatics to dilate the pupil and prevent adhesions.
• Therapy of the underlying disease with systemic causes.

Early diagnosis by an ophthalmologist is crucial to prevent damage to vision and detect problems at an early stage.

Congenital or acquired iris defect

An iris defect can be congenital or caused by injury, disease or surgery. Congenital defects such as an iris coloboma (a cleft-like opening) occur during embryonic development. Acquired defects, such as a tear in the iris following trauma, can affect the regulation of light incidence and lead to glare or vision problems. Depending on their severity, iris defects are treated with special contact lenses, surgical procedures or implants to restore iris function and vision.

Glaucoma and the role of the iris

Glaucoma is an eye disease in which the intraocular pressure rises and can damage the optic nerve. The iris plays a central role as it influences the outflow of aqueous humor from the anterior chamber of the eye .

If the iris blocks the outflow channels (trabecular meshwork), as is the case with angle-closure glaucoma, the aqueous humor builds up. This leads to a dangerous increase in pressure. Anatomical features of the iris, such as an unusually thick structure, can also increase the risk of glaucoma.

Treatment includes medication to reduce intraocular pressure, laser therapy or surgery to improve the drainage of aqueous humor. Regular check-ups with an ophthalmologist are crucial in order to detect glaucoma at an early stage and preserve vision.