What Determines Your Eye Color?

Created on: Monday, September 09, 2013
Author: Shepard Eye Center

Tags: eye, color, melanin, pigment, iris

What is it exactly that gives you your eye color?  It's not as simple as you may think.  All eye color is dependent on a pigment in your iris called melanin.  Your iris and its pigment regulate how much light enters your eyes, and protect against UV rays.  The less melanin there is in the iris, the lighter the eye color will be.  This means that people with dark brown eyes have the most melanin, and people with green, gray, or blue eyes have the least.  There are also some rare anomalies when it comes to eye color, such as heterochromia and the eyes of albinos.
Heterochromia means that you either have a distinctly different color in each eye, or two different colors in the same eye; for example, if someone had heterochromia, they might have a brown eye on one side, and blue on the other.
 

 
Heterochromia in two different eyes

 

 

 

Heterochromia in the same eye

 

 

 

 

Albinos have unique red colored eyes caused by a lack of the melanin pigment, which means that their iris is actually clear, but appears red because you can see the blood vessels of the eye through the iris.
 
 

 
 
Transparent iris in the eye of an albino

 
 
We now know that eye color is determined by melanin, but what determines the amount of melanin in your iris?  It all comes down to genetics.  The genes that produce darker eyes typically dominate light-eye genes, but it’s not really that simple.  Different combinations of differently colored DSCR9, 17q25.3, LYST, OCA2, HERC2, and Gey genes have different effects on your iris’ melanin, but the details are complex, so we won’t go into it here.  
In the entire world, there are no two people who have the exact same eye color.  Also, your eye color can change throughout your life, starting at the beginning.  Babies are born without normal amounts of melanin, which is why their eyes are usually blue or gray, and then change to their true color usually within a few years.  A change in eye color can also be an effect of age, trauma, or disease, and when your pupils change size, the pigment in your iris compresses or spreads apart, causing a slight change in color. 
Your eyes can also reflect images and colors around you, so your eye color can look different depending on what color you are wearing or the color or lighting in your immediate environment.  As you can see, there are a lot of factors that go into the color of your eyes, making your own truly unique.


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