Do You Have One of the 6 Rarest Eye Colors in the World?

Eye color is primarily decided by the amount and distribution of a brown pigment called melanin in your iris. The iris is a ring-shaped membrane behind the cornea, responsible for dilating and contracting your pupil, letting the right amount of light into your eye. The iris is made of an intricate web of muscle and connective tissue. The pigment of your iris is expressed with melanin: Dark brown eyes have a lot of this pigment, light brown eyes contain less and light blue eyes contain very little.

So, Elizabeth Taylor didn't have purple pigment in her eyes. If you have lighter colored eyes, it mostly points to a lack of melanin in the front or back layer of your iris. The amount, coupled with the distribution of melanin within these layers and the way light scatters through the layers, results in eye color.

"Dark iris color is associated with less scattering of light in the eye," says Usiwoma Abugo, M.D., spokesperson for the American Academy of Ophthalmology and ophthalmologist at Virginia Eye Consultants. "This trait may be protective under conditions of bright sunlight and high UVR, like for people who live in the equatorial regions of the world. Blue eye color, on the other hand, is associated with greater light scattering in the eye and a higher level of melatonin suppression, traits that may have been adaptive under highly seasonal sunshine regimes in northwestern Eurasia."

How people end up with their own unique eye color is complicated, but genetics has a lot to do with it. Research has discovered that up to 16 genes determine eye color, but two located on chromosome 15 influence it the most.

"People used to believe eye color could be easily determined based on your parents' eyes, but the genetics of eye color is actually much more complicated," says Abugo. "Research has shown that the color of your eye may actually be linked genetically to the color of your skin and hair in some cases. Basically, the color of your eye is determined by a complex mix of genes, some of which are still being studied."

Brown is the most common eye color in the world — between 70 and 80 percent of the world's population have eyes that are some shade of brown, from the darkest dark brown to light brown. It's thought that all ancient humans living 10,000 years ago or more had brown eyes. The first light-eyed person probably had a genetic mutation that caused their body to produce less melanin, and this mutation was passed on to their descendants.

Here are the six rarest eye colors in the world:

The rarest eye color in the world isn't just one color — it's two. People with a condition called heterochromia iridis have irises of two different colors. Less than one percent of the world's population has heterochromia, and there are three different types:

An infant can be born with heterochromia and have completely healthy eyes, but it can also be aquired later, as a symptom of another disease or syndrome like Horner Syndrome or Sturge-Weber Syndrome. Heterochromia can also be acquired through eye injuries or diseases like glaucoma.

Violet eyes are extremely uncommon, and they often point to an underlying condition: albinism. A genetic condition in which a person is born with little or no melanin in their entire body, albinism affects the appearance of skin, hair and eyes. The lack of pigment makes the eyes of a person with albinism extremely sensitive to light, which can lead to poor eyesight, among other eye conditions.

The eyes of those with albinism can appear pale blue, purple or even reddish in some lights as the result of light reflecting off blood vessels in the eye. When just a very little bit of melanin is present, these red reflections mix with the pigment to create violet eyes.

Green eyes are considered by many to be the rarest eye color, with only 2 percent of the world population sporting this eye color. Green eyes are far more common in parts of Europe than in the world at large, and women have them more often than men.

For green-eyed people, both the front and back layer of the iris have a low concentration of melanin. This light pigment mixes with light, causing it to scatter with a similar effect to the one that causes the sky to look blue. This blue light mixing with the melanin produces green eyes.

Historically, gray and blue eyes have been combined, but recently researchers have discovered there are some marked differences. Around 3 percent of the world's population have gray eyes, and like most light-colored eyes, the coloration is the product of very little melanin in the iris. Unlike the case with green eyes, the front layer of the iris, called the stroma, has no pigment at all. However, gray eyes have more collagen in the stroma than other colors, affecting the way light scatters within the iris.

Although there's not much data on hazel eyes, it's thought that around 5 percent of the world's population have hazel eyes. Hazel eyes have a moderate amount of melanin dispersed throughout the iris. Combined with the scattering of light that changes the appearance of the color depending on the light conditions, the melanin in hazel eyes generally presents a speckled greenish-brown color.

Blue eyes are relatively common — between 8 and 10 percent of people in the world have blue eyes. However, the fibers of the stroma in blue-eyed people have no melanin at all, causing the maximum amount of light to scatter, and more blue light gets back out of the iris than any other color.

One cool thing about blue eyes is that, since they have no blue pigment at all, the way they look depends entirely on available light. This is called structural color, and it's what gives butterfly wings their color.