Eye color can change, though significant or permanent alterations in adulthood are uncommon and usually linked to specific physiological or medical factors. The iris is the colored structure of the eye, a delicate diaphragm that regulates the amount of light entering the pupil. The color we perceive results from light interacting with the pigment and structure within the iris. While a color shift can be a natural process, a noticeable and lasting change in one or both eyes warrants an examination by an eye care professional.
How Pigmentation Determines Eye Color
The actual color of the iris is determined by the amount of melanin pigment present and how light scatters within the eye’s structure. Melanin is contained within the iris stroma, the layer at the front of the iris. Higher concentrations of melanin absorb most light, resulting in darker colors like brown, which is the most common eye color globally.
Eyes that appear blue or green contain much lower amounts of melanin in the stroma. The blue color is not caused by a blue pigment but by a phenomenon called Rayleigh scattering, the same effect that makes the sky appear blue. When light enters an eye with low melanin, the shorter, blue wavelengths scatter back out of the stroma, creating the blue appearance. Green eyes are an intermediate case, combining this light scattering effect with a small amount of yellowish pigment.
Physiological Changes During Development and Aging
The most dramatic and common eye color change occurs naturally during human development, specifically in infancy. Many babies of European descent are born with light blue or gray eyes because the melanocytes, the cells that produce melanin, have not yet fully activated. These cells require exposure to light to begin producing and depositing pigment into the iris.
This process of melanin deposition usually causes the eyes to darken, often shifting to green, hazel, or brown. The most noticeable changes occur between six months and one year of age. While the color typically stabilizes by age three, subtle shifts can continue into adolescence and early adulthood for a small percentage of people.
Aging can also bring about subtle changes in eye color. Over decades, the accumulation of substances like lipofuscin, a yellowish “wear and tear” pigment, can affect the iris’s appearance. Similarly, a slight fading or dulling of color may occur in some individuals due to changes in the density of the stromal tissue. These age-related alterations are usually minor and occur gradually over a long period.
Medical Conditions and Medications That Alter Color
A sudden or noticeable change in eye color in an adult may signal an underlying medical issue affecting the iris. For instance, a condition called Fuch’s heterochromic iridocyclitis involves chronic, low-grade inflammation that often leads to a loss of pigment in the affected eye, causing it to lighten. This can lead to acquired heterochromia, where the eyes are two different colors.
Pigment dispersion syndrome is another condition where pigment granules flake off the back of the iris and float into the eye’s fluid, potentially resulting in a lightening of the iris color. Conversely, conditions like Iridocorneal Endothelial (ICE) syndrome can cause cells from the cornea to migrate to the iris, creating spots or irregularities that alter the eye’s appearance. Eye trauma or injury can also directly damage the iris tissue, leading to permanent structural and color changes.
Certain medications are also known to cause permanent changes in iris color. The most well-documented examples are prostaglandin analog drops, which are commonly prescribed to treat glaucoma by lowering internal eye pressure. These drops can stimulate increased melanin production in the iris, leading to a gradual and irreversible darkening, often shifting light-colored eyes toward a brownish hue. This effect is more pronounced when the drops are used in only one eye.
Perceived Shifts and Intentional Alterations
Many perceived changes in eye color are due to external factors or visual illusions, not physical alteration in the iris. The color of the clothes a person is wearing, the surrounding lighting, or the application of makeup can influence how the eye color is reflected and perceived by an observer. These are temporary optical effects that do not represent a true change in the iris’s inherent pigmentation.
The size of the pupil also influences the apparent color of the eye. When the pupil constricts, the colored part of the iris appears larger and more prominent. Conversely, when the pupil dilates in dim light, it reveals less of the iris, making the remaining color appear more intense or darker against the large black center. This constant change in pupil size, driven by light levels and emotional states, contributes to the impression that eye color is constantly shifting.
For those seeking a deliberate color change, the most common method is the use of colored contact lenses, which are purely cosmetic and sit on the surface of the eye. More permanent, intentional alterations, such as cosmetic iris implants or laser procedures to remove pigment, are available but are generally considered high-risk medical procedures for aesthetic purposes and are not widely endorsed by eye care professionals.