The eyes are a magical part of the body. While the concept of how the body bends its fingers or digests food are fairly easy to understand, the idea that these moist little spheres are capable of sight is remarkable. But it’s more than just being able to see; it’s judging depth, color, and discerning objects with even the least amount of light. If that wasn’t enough, the color dynamics found in the iris are both mesmerizing and beautiful. But why do we have different colored eyes? Why is there color at all. Today, Marano Eye Care in New Jersey will explore the depths of eye color and the function of the iris. Keep your eyes peeled!
Let’s start with where eye color resides, in the iris. The iris is a ring-like and flat membrane that sits behind the outer cornea. This muscular little membrane works in tandem with the pupil to regulate the amount of light that passes into the eye. If there’s too much light or too little, vision can be impaired or even damaged.
Because the iris is a key component in filtering out the light that enters our eyes, it makes sense that the iris would need protection. In humans and animals, that protection comes in the form of melanin. Melanin is derived from a form of amino acids called tyrosine. Typically ranging from black to brown, the pigments in melanin absorb light to filter it away from more sensitive parts of the body. This protection goes as far as protecting our DNA from the Sun’s UV radiation. Melanin is found all over the body, including hair, the eye, skin, and even parts of the inner ear and brain! The easiest way to see melanin in action is to spend some time in the sun. With enough exposure, your skin will begin to tan – that’s the melanin building up pigment to protect you.
You might be thinking, “well that covers brown eyes, but what about other colors?” Well, here’s where evolution and history comes into play.
About 10,000 years ago, the earliest humans in the world all had significant amount of pigment in their eyes and everyone’s eyes were brown. But then, genetic mutations began to affect certain genes and reduced the amount of brown pigments being produced in the front of the iris. It’s a very complex phenomenon, but the combination of reduced pigments, textures within the iris, blood vessel and fibrous tissue reflect back light as the color blue.
For colors such as green, gray, or olive, these are halfway colors that are caused by more pigment than blue eyes, but less than brown. These days, there are so many colors of eyes to behold, that scientists have added several gradients to their color scale beyond blue, green, or brown.
If you’re interested in learning more about the genetics that impact eye color, the following is a thorough, but complex report.
Image via Oddity_Olive
Cat with Sectoral Heterochromia. Image via Oddity_Olive
Given how complicated the process is for each person’s eyes gain their color, it’s not surprising that there are some rare and unique colorations that pop up from time to time. Here are a few of the most rare and interesting.
Amber colored eyes may be seen in cats and other species on a regular basis, but it’s very rare in humans. People with solid orange/gold eyes have a unique pigment called pheomelanin dominant within the iris. While it’s also found in people with green eyes, it’s a much smaller amount.
People with albinism have been born with a congenital disorder related to pigment production in their bodies. Albinism may cause a person to have either partial loss of pigment or complete loss. This deficiency carries over to the eyes. Because there is no pigment to cause the iris to appear opaque, you are able to see the red of the retina.
Unfortunately, people with albinism are subject to various eye conditions, such as crossing of the optic nerve fibers, decreased visual acuity, and light sensitivity.
Like amber eyes, heterochromia is much more common in animals, such as cats, dogs, and horses. Heterochromia is more commonly known as odd eyes, where each eye has a different colored iris. Sectoral heterochromia is rarer amongst all species. This causes each iris to be a different color within each eye. Few people have ever seen it in public, but if you do, it will merit a second glance.
Heterochromia is again caused by either inherited genes, disease, injury, or another sort of mutation.
At Marano Eye Care, we’re fascinated by everything ocular! If you live near Denville, Livingston, or Newark, make an appointment for a complete eye exam today! Eye health is imperative to your quality of life, so the choice is clear. Call 973-322-0100 today!