Why are blue eyes blue?

June 27, 2011 — by William Goldstein
Tags: Contact Lenses Blue Eyes Colored Contacts Dr William Goldstein Brown Eyes

The sappy 70's song "Don't it make my brown eyes blue" inevitibly leads us to think about whether brown eyes can be turned blue. Maybe the song was inspired by colored contact lenses! But why are there variations in eye color? Why are there so few blue-eyed people?

An article in the journal Human Genetics from 2008, indicates that blue eyes are the result of a single gene mutation that occurred between 6000 and 10000 years ago. The article was written by a cellular molecular biologist, Hans Eiberg.

"A genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a 'switch,' which literally 'turned off' the ability to produce brown eyes," Eiberg said.
The genetic switch is located in the gene adjacent to OCA2 and rather than completely turning off the gene, the switch limits its action, which reduces the production of melanin in the iris. In effect, the turned-down switch diluted brown eyes to blue.
In some patients, this switch is completely off, and their bodies do not produce any melanin. These people are known as albinos, and have the characteristic white hair, and skin, as well as irises that have no color.

So, if brown eyes are from melanin, which is brown, how does lack of melanin cause blue eyes? This is because the deeper layers of the iris absorb most wavelengths of light, while allowing the blue wavelangths to reflect back to the observer. So there is actually no blue pigment in the iris of blue-eyed people!

Dr. William Goldstein provides the best in eye care. Call now to make an appointment, 586-899-9393, or visit the website, www.2020vision.com