Table of contents:
- What makes people's eyes different colors?
- Then, why are there so many kinds of bright eye colors?
- There are people who have two different eye colors
You may often notice that there are people with blue eyes, some green, gray, and some dark brown. Not because you wear color contact lenses, you know! Their eye color is the original eye color they are born with. Usually, blue and green eyes are owned by white people, aka Caucasians, while brown and black eyes are typical of Asian people. Why is everyone's eye color different, huh?
What makes people's eyes different colors?
The colored circle in the middle of the eye is called the pupil. Pupil color is determined by dye cells called melanocytes. The lightness of your skin and hair color is also determined by these melanocyte cells.
In the eye, melanocyte cells gather in front or behind slices (see eye anatomy image below). The pupil is right in the center of the iris.
Source: All About Vision
Melanocyte cells themselves consist of two types of pigments, namely eumelanin (producing brown color) and pheomelanin (producing red color). The more eumelanin in your iris, the darker your eye will be. As many as 55% of people in the world have dark brown eyes. Conversely, the more pheomelanin in your iris, the lighter your eye color will be.
Then, why are there so many kinds of bright eye colors?
Eyes that are originally bright in color, for example blue, green, purple, to gray occur because melanocyte cells accumulate behind the iris. The light that the iris receives then bounces back, giving the pupil a blue (or other light color) impression. Meanwhile, dark colored pupils (dark brown or black) occur because melanocyte cells accumulate in the front layer of the iris, which absorbs light.
In addition, the variation in eye color is also determined by how much melanin pigment is in the iris. Blue and green eyes, for example, have different amounts of pigment. Reporting from the Livestrong page, green-eyed people have less pigment than brown eyes, but more than blue-eyed people. There are also certain parts of the iris that are not pigmented.
Green is the rarest eye color in the world. It is estimated that only about 2% of the human population has green eyes.
Like many traits, the amount and type of melanin pigment in your eyes is controlled by the genetic makeup of your parents. Based on research led by Manfred Kayser, a professor in molecular forensics from Erasmus University Medical Center Rotterdam, so far 11 genes play a role in determining the color of the two human eyes.
There are people who have two different eye colors
Six out of a thousand people in the world have a pair of eyes that are a different color between their right and left - one blue eye and one green eye, for example. This condition of two different eye colors is called heterochromia.
Heretochromia (source: shutterstock)
Heterochromia is generally a condition that is congenital at birth (genetic). The difference in the color of the two sides of the eye does not affect visual acuity. However, this condition may also be a sign of an eye disease, such as chronic iritis, uveitis, or diffuse iris melanoma, or the result of eye injury and the use of certain glaucoma medications.
