Ten percent of the population does not have blue eyes… it’s all an illusion caused by the ‘Rayleigh Effect’. According to the effect, there is an absence of pigment and from it comes the illusion of blue.
The lack of pigment combined with a physical phenomenon is what makes it look the way it does. In other words, your irises are colorless.
Blue eyes, an explanation for the incongruence
The effect that dominates blue eyes is also behind the reason why we see the sky blue, as the wavelengths of blue light from the sun scatter through the atmosphere until they reach our eyes and, as a result, we see the sky with that hue and so do our eyes.
To understand it better, let us remember that color is a matter of light, colors are nothing more than the way in which our eyes interpret the light that reaches them, coming from the different objects that surround them. Therefore, colors are simply light.
We do not see colors as such, but we see wavelengths. The iris, which is the colored part of the eye, contracts and expands to regulate the passage of light through the pupil. It consists of two layers and, in almost everyone, the back layer, the pigment epithelium, contains brown pigment.
Therefore, the protagonist in this shade appearance is the second layer, the stroma, which is composed of a series of overlapping fibers and a large number of specialized cells.
The gene was interrupted
Between 6,000 and 10,000 years ago an alteration occurred in the human gene. In fact, in one individual “a genetic mutation that affected the OCA2 gene (involved in the production of melanin) in our chromosomes,” explained the director of the original study, Hans Eiberg of the University of Copenhagen, in 2008.
That mutation created a genetic switch that turned off that ancestor’s body’s ability to produce brown pigment in their eyes. So all blue eyes can be traced back to an ancient common ancestor, from which the characteristic of having no melanin in the stroma was inherited.
That means that that top layer of the iris is translucent, but we are still left with the question that there is no other pigment that gives blue color, other than light.
The fiber structure of the stroma scatters light in a similar way, tending to scatter short wavelength light more than long wavelength light.
When visible white light reaches it, blue scatters more than other colors because it travels as shorter waves.
This is why the same pair of blue eyes may look more vibrant at certain times than at others; their color depends on the quality of the light in the place they are in.
This story was originally published in Spanish by Perla Vallejo in Ecoosfera.
