The human eye comes in various shades of brown, almost black, green, blue, hazel, and violet. The color of the eyes develops just as an infant grows. The final eye color of a person will depend on the genetic combination of his or her parents. That said, the influences of the parents are never known until after the child is born.
How Eye Color Develops
The iris is the colored part of the eye. It determines a person’s eye color. The human eye color originated from three genes. However, only two genes are understood and studied. How the third gene works remain a mystery. The fact is, there is a very complex process that results in the final eye color of a person. The colors do not simply come out from a blended combination of both parents’ eye colors. Multiple eye color combinations exist because each parent has 2 pairs of genes on each chromosome.
A person’s eye color will depend on the pigmentation of the iris as he or she grows. Initially, Caucasian infants are born with blue eyes that darken continuously during the first three years of life. On the other hand, African and Asian infants are born with light brown to almost black irises, which are their final color.
The darkening of the iris is caused by the level of melanin in the eyes. Melanin is a brown pigment that also darkens the skin. Each person generates different amounts of melanin and this will affect the skin, hair, and eye color.
Factors that Affect Eye Color
At the most basic level, your eye color is caused by the amount of melanin your irises have. This pigment is found in either the front or the back layer of the irises. The location of the melanin can also affect your eye color. For instance, blue-eyed people have zero melanin in the front layer of the irises, just the back layer. Brown eyed people have more melanin in the front layers of the iris. Green or hazel-eyed people have more pigment on the front layers than blue-eyed people but less when compared with brown-eyed folks.
According to scientists at the Hudson Alpha Institute for Biotechnology, there are at least 8 different genes that control the eye color of a person. But the most important gene of them all is the OCA2 gene. This gene determines whether the eye will possess brown or blue eye color.
OCA2 gene is located on chromosome number 15. It produces a type of P-protein that generates and process melanin. The amount of melanin secreted by the P-protein will affect a person’s eye color. Other genes come into play and this explains while some parents with light eye colors occasionally have a dark-eyed offspring. Studies show that blue eyes were a recent development in human history. The variant of blue eyes occurred between 6,000 to 10,000 years.
Diseases, Medications, and Treatments
Yes, certain types of diseases can affect a person’s final eye color. For instance, Fuch’s heterochromatic iridocyclitis, Horner’s syndrome or pigmentary glaucoma can cause subtle to dramatic changes in a patient’s eye color. All these color changes require medical evaluation. Some types of medications can also alter a person final eye color.
There are times when natural aging affects the final eye color of a person. The amount of melanin in the eyes can increase or decrease as we age. In fact, 10% to 15% of Caucasians experience color changes of the irises as they age.