Many wonder if eye color can change, particularly if brown eyes can turn blue with age. While eye color generally remains stable in adulthood, its appearance can be influenced by certain conditions or, rarely, genuine alterations.
How Eye Color Is Determined
Eye color is primarily determined by the amount and distribution of melanin, a pigment, within the iris. The iris is the colored part of the eye surrounding the pupil. More melanin in the iris results in darker eye colors, such as brown, while less melanin leads to lighter colors like blue or green.
Genetics play a significant role in influencing melanin production. Over 16 genes contribute to eye color, with OCA2 and HERC2 being particularly impactful. The perceived color also arises from how light interacts with the melanin and the structure of the iris. For instance, blue eyes have low melanin content, and their color is largely due to Rayleigh scattering, a phenomenon where shorter blue wavelengths of light are scattered more than others, similar to how the sky appears blue. Brown eyes, conversely, have high concentrations of melanin that absorb most light, resulting in their dark appearance.
Why Adult Eye Color Stays Consistent
Melanin production in the iris typically stabilizes during early childhood. After a few years of age, eye color generally remains consistent throughout adulthood, preventing natural, age-related shifts.
Infant eye color can change significantly during their first months or years as melanocytes, the cells producing melanin, are still developing and producing pigment. However, this developmental phase concludes, and the amount of melanin in the iris usually becomes fixed. Brown eyes, characterized by a high and stable concentration of melanin, are particularly resistant to natural lightening.
Factors That Can Influence Eye Appearance
While actual eye color, determined by melanin, does not typically change in adulthood, its appearance can seem different due to external factors. Lighting conditions, such as natural sunlight versus artificial light, can alter how eye color is perceived. Different light sources scatter and reflect light differently, making the iris appear to shift in hue.
Changes in pupil size can also influence perceived eye color. When pupils dilate, they expose more or less of the iris, making the eye color seem lighter or darker. These are perceptual changes, not actual alterations to the melanin content or structure of the iris itself.
Actual Causes of Eye Color Change
Genuine changes in eye color during adulthood are rare and typically indicate an underlying medical condition, injury, or medication side effect. One such condition is heterochromia, where eyes or parts of an eye have different colors. This can be congenital, present from birth, or acquired later in life.
Acquired heterochromia can result from conditions like Fuch’s heterochromic iridocyclitis, an inflammation of the iris, or Horner’s syndrome, which affects nerve pathways to the eye. Pigment dispersion syndrome, where pigment flakes off the iris, can also cause changes. Certain medications, notably prostaglandin analogs used to treat glaucoma, can lead to increased iris pigmentation, causing eyes to darken over time. Eye injuries, bleeding in the eye, or tumors can also cause permanent changes in iris pigmentation or structure.