Eye color can indeed shift under specific circumstances. While significant changes are a normal part of development in infants, alterations in adult eye color are less common. Understanding the factors that influence eye pigmentation helps clarify when a change is typical and when it might signal a health concern.
How Eye Color is Determined
Eye color originates from the iris, the colored part of the eye. Melanin, a pigment also responsible for skin and hair color, primarily determines eye hue. The amount and type of melanin in the iris’s front layers dictate the final color. Brown eyes have a large amount of melanin, while green and hazel eyes have less. Blue eyes have very little melanin; their appearance results from Rayleigh scattering, where shorter blue light wavelengths are scattered by the iris’s fibrous tissue.
Why Infant Eye Color Can Change
Many babies are born with blue or grayish eyes because their melanocytes, the cells that produce melanin, are not fully activated at birth. These cells begin producing pigment only after light exposure. As infants are exposed to more light, melanocytes gradually increase melanin production, causing eye color to darken. This can lead to changes from blue to green, hazel, or brown. This dramatic change typically occurs between 3 and 6 months, though subtle shifts can continue up to 3 years, as a normal part of growth.
Factors Affecting Adult Eye Color
While adult eye color generally remains stable, various factors can cause it to appear different or genuinely change. Environmental lighting and surrounding colors can create an illusion of a color shift. Pupil dilation due to strong emotions can also make eyes seem darker or more intense. True changes in adult eye color are rarer, sometimes occurring over many decades due to gradual shifts in iris pigment cells.
However, more significant alterations often point to an underlying medical condition. For instance, new onset heterochromia, where one eye becomes a different color from the other, can result from injury or disease. Specific medical conditions that can cause changes include:
Fuchs’ heterochromic iridocyclitis, an iris inflammation causing pigment loss.
Horner’s syndrome, nerve damage leading to a lighter iris, particularly if developed in childhood.
Pigmentary glaucoma or pigment dispersion syndrome, causing pigment to shed from the iris.
Uveitis, an inflammation of the eye’s middle layer, leading to iris color changes, sometimes with pain or redness.
Certain glaucoma medications, like prostaglandin analogs, which can cause irreversible iris darkening due to increased melanin deposits.
When to Consult a Doctor About Eye Color Changes
Any sudden or rapid change in the color of one or both eyes in adulthood warrants medical attention. This is especially true if accompanied by other symptoms such as eye pain, redness, blurred vision, or increased sensitivity to light. Noticing a new difference in color between your two eyes, known as acquired heterochromia, should also prompt an ophthalmologist’s evaluation. While minor, gradual lightening or darkening over a lifetime, or perceived changes due to light, are usually not concerning, any noticeable or symptomatic changes should be assessed by an eye care professional.