Eye color is as unique and distinctive as each person’s fingerprints. You may see those around you with brown or black eyes like yours, but that eye color is undoubtedly different. You might have also noticed many people born with blue eyes who later develop brown ones. Why do these differences occur? Below are some explanations.
What Does Eye Color Indicate?
The eyes are the windows to the soul, but they also serve as a portal to genetic inheritance. The iris, the primary part that gives color to the eyes, is responsible for regulating the amount of light that reaches the retina by changing the size of the pupil. But why does the iris have different colors?
How is Eye Color Formed and Changed?
The most common eye color is brown, followed by blue or gray.
The color of the eyes is determined by the amount of a pigment protein called melanin in the cells of the iris. A child born with little to no melanin in the iris will have blue eyes. Between 6 to 36 months, the cells in the iris begin to produce melanin, changing the color of the eyes. If there is too much melanin, the eyes will be brown; if there is little melanin, the eyes will remain blue. Most children in Asia and Africa are born with brown or black eyes because melanin is already present in abundance in their irises. However, occasionally, some children are born with blue eyes.
Common and Rare Eye Colors
Eye color is not limited to just green, blue, and brown; it has many shades. The most common eye color is brown, followed by blue or gray. Green eyes are considered rare, while red eyes are extremely rare. Red eyes appear almost devoid of melanin, making the iris colorless, but the eyes appear red or pink due to the color of the blood vessels. Some individuals may have two different colored eyes because their irises are formed from two different gene types. This phenomenon occurs due to random combinations of genes or injuries that disrupt melanin production. Two-colored eyes are rare in humans but are found in dogs, cats, and horses.
What Determines the Concentration of Melanin in the Iris?
It all depends on genes. According to previous theories, eye color was determined by a single gene. If a father has brown eyes and the mother has blue eyes, their child would have blue eyes. Modern science reveals that multiple genes significantly influence eye color. These cells control the amount of melanin in the iris. The two main genes responsible for eye color are OCA2 and HERC2. The OCA2 gene determines about three-quarters of the eye color spectrum from blue to brown. A child’s eye color depends on the combination of these two sets of genes.
Unlike hair and skin, eyes do not continuously produce melanin. Therefore, depending on the concentration of melanin in the surrounding fatty tissue, the eye color can appear lighter or darker.
Can Eye Color Change?
The color of the iris can change if there are other colors nearby; for example, applying different eyeshadow colors can “fool” us about the person’s actual eye color.
The color of the iris does not remain constant throughout life. Newborns with blue eyes can change to brown or hazel just one day after birth due to the production of darker pigments in the iris cells post-delivery.
The color of the iris can also change due to certain diseases or injuries.
Some eye drops used to treat glaucoma may produce more brown pigments in the iris cells, making the eyes appear browner. Some people are born with one brown eye and one blue eye, and this never changes throughout their lives, although the reasons for this are not yet fully understood.
