It is a common belief that eye color changes with age, often imagined as a fading process. While eye color can shift, the underlying reasons are more nuanced than simple fading.
The Science Behind Eye Color
Eye color originates primarily from melanin, a pigment also responsible for skin and hair color. The amount and distribution of melanin within the iris, the colored part of the eye, determine its hue. Brown eyes, for instance, contain a higher concentration of melanin in both layers of the iris. In contrast, blue or gray eyes have very little melanin in the front layer of the iris.
Beyond melanin, the scattering of light within the iris plays a significant role in how eye colors like blue and green are perceived. This phenomenon, similar to Rayleigh scattering, causes shorter wavelengths of light (blue and violet) to be reflected more prominently. Green eyes result from a combination of low to moderate melanin in the iris stroma and this blue scattering effect. The interplay of melanin content and light scattering creates the diverse spectrum of human eye colors.
Age-Related Eye Color Changes
For most people, significant fading of eye color in adulthood is uncommon. In some instances, eyes may actually darken slightly over time due to a gradual accumulation of melanin. This can occur from prolonged sun exposure, which stimulates melanin production, similar to how skin tans.
A more notable and common eye color change occurs during infancy. Many babies are born with lighter eyes, often blue or gray, because their melanin production is not yet fully developed. As infants are exposed to light, melanocytes—the cells that produce melanin—become more active, leading to increased melanin in the iris. This process typically causes eye color to darken, often settling into its permanent shade by 6 to 9 months, though subtle shifts can continue up to three years of age.
Other Causes of Eye Color Alteration
Beyond typical aging, several factors can genuinely alter eye color. For example, Horner’s Syndrome, a rare condition resulting from nerve damage, can cause the affected eye to become lighter due to a lack of pigmentation. Fuchs’ heterochromic iridocyclitis, an inflammatory condition, can also lead to a loss of iris pigment. Pigmentary glaucoma, where pigment flakes off the iris and can clog drainage angles, might lighten parts of the iris. Uveitis, an inflammation of the eye’s middle layer, can also cause changes in iris color, sometimes darkening it.
Medications are another potential cause. Prostaglandin analogs, used in glaucoma eye drops, are known to permanently darken eye color, especially in individuals with lighter irises. This darkening is due to an increase in melanin content within the iris. Additionally, eye injuries or trauma can damage the iris, leading to tissue loss or depigmentation.
When to Seek Medical Advice
While minor, gradual changes in eye color are typically harmless, certain alterations warrant medical attention. If you notice a sudden, dramatic, or asymmetrical change in eye color in one eye compared to the other, consult an eye doctor. This is particularly important if the color change is accompanied by other symptoms, such as eye pain, vision changes, redness, light sensitivity, or changes in pupil size or shape. These symptoms could indicate an underlying medical condition that requires prompt evaluation.