Why does the color of the iris differ from person to person? In this article, Dr. Zwillinger and her multidisciplinary COP9 team introduce you to the characteristics of the iris, the colored part of the eye, while also raising awareness of ocular albinism, a unique case of iris coloring.
To understand better the colors of the iris: what is the iris?
In the eyeball, the iris is a membrane located between the cornea and the lens. In the center of the iris is an opening, called the pupil, which can be recognized as a central black spot.
The iris is surrounded by two smooth muscles: one will stretch the membrane, the other will contract it. These movements serve to adjust the size of the pupil to control the amount of light entering the eye.
To use a precise ophthalmological terminology, we will call this phenomenon :
- mydriasis when the pupil is dilated;
- myosis when the pupil contracts.
In this membrane are located pigment cells whose number and disposition create a panel of varied colors for the iris: blue, green, brown, black…
In the case of ocular albinism, these pigmentations are absent. The iris appears light blue or transparent: feel free to discover more information in the last part of our article!
the colors of the iris do not play a role in the need for optical correction, if you observe any difficulty in your visual field, do not hesitate to make an appointment for further ophthalmic testing.
What gives our eyes their iris colors?
The colors of the iris evolve with time: this change is frequently noticed in newborns and children. However, this phenomenon is more rare in adults.
Two factors should be taken into account to better understand the colors of the iris:
- Genetic factors, including the quantity of melanin present in the iris;
- Physical factors, such as light reflection.
Even though it may look like two people with blue eyes, they will not be alike. The fine channels that make up the iris are very different from one person to another, and even from one eye to another.
However, it is extremely rare for an individual to have different colors of the iris from one eye to the other. This very rare case is known as ” odd eyed “.
Ocular albinism: a particular case of iris color.
Ocular albinism is often observed at birth by the parents. As soon as there is any doubt, it is necessary to carry out a check-up with a pediatric ophthalmologist, and to perform a genetic check-up.
The main symptoms of ocular albinism are:
- A defective vision (myopia, astigmatism, hyperopia);
- A partial or total deficit of pigmentation of the eyes;
- Sometimes accompanied by skin depigmentation (called oculocutaneous albinism).
For the eye to develop in good conditions, it must resemble a “dark room” which corresponds to the vitreous cavity of the eye, sensory tissue “the retina”, and finally, an opening in front of the eye “the pupil” controlled by a diaphragm “the iris”.
We can compare the eye to a photographic darkroom: the inside of the eyeball is lined with the pigment epithelium, whose pigmented cells do not allow light to pass through. Thanks to a system of contraction and relaxation, developed in our section “To better understand the colors of the iris: what is the iris?”, the quantity of light entering the eye is controlled.
However, in the case of ocular albinism, there is a deficit of these pigmented cells. The eye therefore has more difficulty in creating this dark space to process light and perceived images.
What are the consequences of iris color depigmentation?
When an albino eye is observed, the colors of the iris are almost translucent blue. By retro-illumination, or during ophthalmologic examinations, the visual health professional will notice that the eye can become red.
Beyond this aesthetic consequence, the person with ocular albinism will have an almost constant state of being dazzled. This constant superposition to the light prevents a normal stimulation of the retina.
This pigmentation defect has consequences on the development of the visual system:
- poor eyesight;
- nystagmus ;
- strabismus.
There is no treatment for this iris color disorder and it requires regular check-ups with the ophthalmologist, making appointments at the frequency indicated by the practitioner.
Ocular protection, but also skin protection is necessary to avoid any complications: because of the melanin deficiency, albino people are very sensitive to the sun’s rays! Protecting the eyes from the sun is therefore essential, especially in this case of depigmentation of the iris colors.
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