It is a common question whether eye color can change over a person’s lifetime. While eye color is largely stable for most individuals, specific circumstances can lead to genuine alterations or the perception of a change.
The Science of Eye Color
Eye color, specifically the color of the iris, is primarily determined by the amount and distribution of melanin, a pigment also responsible for skin and hair color. Specialized cells called melanocytes produce melanin within the iris. The concentration of melanin dictates the hue; brown eyes have the highest melanin concentration, green and hazel eyes have intermediate levels, and blue eyes contain very little melanin.
Beyond melanin, the structure of the iris and how it scatters light, known as Rayleigh scattering, also influences perceived eye color. Eye color is influenced by multiple genes, such as OCA2 and HERC2 on chromosome 15, which control melanin production and regulation in the iris, contributing to the wide spectrum of human eye colors.
Eye Color Evolution in Infancy
Many babies are born with eyes that appear blue or gray. This initial lighter color is due to the low levels of melanin present in their irises at birth. Melanocytes have not yet been fully exposed to light.
As an infant is exposed to more light in the months following birth, melanin production in the iris increases. This accumulation of pigment can cause the eyes to darken and change color, often shifting to green, hazel, or brown. While significant changes typically occur between 3 and 9 months, the final eye color can take up to a year or even three years to fully establish. Eyes that are dark at birth tend to remain dark, while lighter initial eye colors are more prone to change.
Adult Eye Color Alterations
Actual changes in adult eye color are uncommon but can occur due to specific medical conditions or certain medications. For instance, Horner’s syndrome, a condition resulting from nerve damage, can lead to heterochromia, where one eye becomes lighter in color. This occurs because the sympathetic nervous system’s stimulation, which influences melanin pigmentation, is disrupted.
Other medical conditions can also cause alterations. Fuchs’ heterochromic iridocyclitis, an inflammation of the front structures of the eye including the iris, can lead to eye color changes. Pigmentary glaucoma, a condition where pigment cells flake off the iris and can block fluid drainage, might also result in subtle color shifts. Additionally, certain medications, particularly prostaglandin analog eye drops used to treat glaucoma, can cause permanent iris darkening. Latanoprost, for example, stimulates melanogenesis in the iris, leading to increased pigmentation, often making lighter eyes appear darker. This darkening typically happens gradually and can be more noticeable in individuals with mixed-color irises.
Perceived vs. Actual Eye Color Shifts
Many people notice their eye color appearing to shift, but this is often a perceived change rather than a true biological alteration. Factors such as lighting conditions play a significant role in how eye color is seen. Natural light, artificial light, and even the intensity of light can make eyes appear different shades.
The color of one’s clothing or makeup can also influence the perceived eye color. For example, wearing certain colors can create an optical illusion, making the eyes seem more vibrant or a different hue due to reflected light or contrast effects. Pupil dilation, which changes the size of the black center of the eye, can also affect how the iris appears, as a larger pupil can make the surrounding iris color seem more intense or different. These influences alter how the eye color is observed, not the actual pigment content within the iris.