Why are my eyes green? Or better yet, why do they change colors?


| 4 Comments
I've always wondered why my eyes looked a certain color.  The older I've gotten, the more attention I've paid to the details.  This has led me to question why my eyes change color, especially at night or depending on my mood.

 

Let's first address what determines eye color.  The short answer is genes - plain and simple.  The slightly more complicated answer refers to the three known genes that are factors in deciding a person's eye color.  According to this source , "there are three known gene pairs that control eye color. The bey 2 gene on chromosome 15 contains a brown and blue allele. Also on chromosome 15, the bey 1 gene is the central brown gene. On chromosome pair 19 the gey gene contains a green allele and a blue allele."  Even more details about these chromosomes can be found here.

 

As you may have learned back in ninth grade biology, dark colors are dominant in eyes.  Brown is dominant while green and blue are recessive, and green is 'more-dominant' than blue.  The same source goes on to say, "A green eyed person would have a green allele on chromosome 19 and all or some other blue alleles. Blue eyes are produced only with two blue eye genes. All four alleles must be blue to produce a blue eyed person." 

 

While much is known in this field, many questions remain a mystery.  This source tells us that the molecules and proteins that make up the genes determining our eye color are still unknown.  It even suggests that there may be yet another gene devoted to green eyes, as many eye colors are not easy to explain through the three chromosomes discussed above.

 Screen shot 2012-10-12 at 10.24.32 AM.png

Photo courtesy of this source


Now that we know what determines eye color, let's talk about what makes it appear a certain way.  The patterns within our eyes that make up each unique pattern are decided by melanin.  Melanin is the same pigment used to make up hair, skin, etc.  Our genes are the instructions for the enzymes in our bodies.  They signal how much melanin should be layered in each iris.  Darker eyes have more melanin, and lighter eyes have less melanin, just as one would expect.  This source explains the layering of melanin in the iris to create each eye color.  There are two parts, front and back, to the iris.  For blue eyes, no melanin is in the front and brown pigment is in the back so when the light reflects and diffracts, it appears blue.  For green eyes, there is a little pigment in the front and the back.  For brown eyes, there is a lot of pigment on the front layer of the iris.  Mixed eye colors (hazels, green/blue mixes, aka my eyes!) are made from the melanin pigments being distribute in different patterns and amounts among the layers (which is less straight forward than the descriptions above).


eye_colour_chart_by_delpigeon.jpg

 

Photo courtesy of The Eye Si(gh)t


Lastly, why do eyes change colors?

 

According to All About Vision, eyes change color when the pupil changes in size (as a reaction to change in light) because the iris is either expanding or compressing with the pupil.  The site also mentions that eye color can change with age, but it doesn't specify why that happens.

 

This brief New York Times article says that eyes can indeed change with age.  It mentions a study on twins and how 10-15% of the identical twins saw changes in eye color, at the same rate, with age. 

 

Every source I read through about eye color changing on a day-to-day basis doesn't seem legitimate.  Most sources have been legends or suppositions that a person's mood is affecting this change.  I have yet to find a source that scientifically backs up this thought. 


Can you help me out by commenting to clear this up?  Can eye color change with mood?  The only common conclusions sites have given me is that mood and environmental influences only change the angle and amount of light, making the iris appear different, but not truly changing.  Does this seem right to you?


4 Comments

You have done a very well research on this subject, and did a nice job at explaining. Based on your explanations, the eye color and its change all occurs because of natural phenomena. But what I found really interesting is this websitet. A company called Stroma Medical developed a way to turn brown eyes into blue eyes, permanently, using laser. It seems that laser releases the brown pigments from the iris, and what the only thing is left would be blue, which develops over the weeks. Science seems to twist then natural phenomena of how things occur, and make them occur in a different color. (excuse the pun)

You have done a very well research on this subject, and did a nice job at explaining. Based on your explanations, the eye color and its change all occurs because of natural phenomena. But what I found really interesting is this websitet. A company called Stroma Medical developed a way to turn brown eyes into blue eyes, permanently, using laser. It seems that laser releases the brown pigments from the iris, and what the only thing is left would be blue, which develops over the weeks. Science seems to twist then natural phenomena of how things occur, and make them occur in a different color. (excuse the pun)

From personal experience, I know my eyes are darker in the winter and lighter in the summertime, which would go along with your environmental change theory. With the little research I did, I found an article which says that people with lighter colored eyes can even change according to what colors they wear. The article also says that some people notice a change in eye color if they are sick or ill.

http://www.eyecarecontacts.com/eyecolor.html

I found your blog post to be very interesting. I, personally, have a connection to the color-changing-eyes phenomenon! I was born with light blue eyes, the exact same color as my father's eyes. My eyes remained this color until around the age of 4- they then changed to a dark green. This change did not happen overnight (according to my parents), but instead was gradual. This is a phenomenon that is somewhat common in Caucasians. According to this article: http://www.allaboutvision.com/conditions/eye-color.htm

This article says that "Eye color also can change with age. This happens in 10 to 15 percent of the Caucasian population (people who generally have lighter eye colors)." I would fall under this naturally-changing category of eyes. When my eyes changed color at my young age, my parents asked my eye doctor if it was anything to be concerned about. I was given a full check-up, and nothing was found to be wrong. This is generally the case with the naturally-changing eyes. I can potentially even expect my eyes to change again as I get older!

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