This question often arises due to various perceived shifts in eye appearance. While eyes do not typically change color in adulthood, certain physiological processes and medical conditions can lead to genuine alterations in iris pigmentation.
The Science of Eye Color
The color of human eyes is primarily determined by the amount and distribution of melanin, a pigment also responsible for skin and hair color, within the iris. This pigmentation is located in the iris stroma, the front layer of the iris.
Brown eyes have a high concentration of melanin that absorbs most light. Blue eyes contain very little melanin; their blue appearance results from the scattering of light within the stroma. Green and hazel eyes result from intermediate melanin levels combined with this light-scattering effect, often involving a mix of yellowish pigments. The specific genetic makeup influences the amount of melanin produced and its distribution.
Real Changes in Eye Color
Many babies are born with lighter eye colors, such as blue or gray, because their melanocytes—the cells that produce melanin—have not yet fully developed. Over the first few months or even years of life, as light stimulates melanin production, their eye color may darken, settling into its permanent shade.
Medical conditions can cause a change in eye color. Horner’s syndrome, resulting from nerve damage, can lead to the affected eye having a lighter iris color, particularly if it develops in early childhood.
Fuchs heterochromic iridocyclitis, an inflammatory condition of the iris, can cause a loss of pigment, making the affected eye appear lighter and potentially leading to different colored eyes (heterochromia). Pigmentary glaucoma involves pigment being released from the iris, which can clog the eye’s drainage system and sometimes result in a lightening of the iris where pigment falls away. Eye injury or trauma can also damage the iris, leading to a visible change in color due to tissue loss or inflammation.
Medications can induce real eye color changes. Certain eye drops, particularly prostaglandin analogs used to treat glaucoma, can cause a permanent darkening of the iris, especially in individuals with blue, green, or hazel eyes. This darkening is often gradual and can occur over several months of treatment.
Cosmetic procedures, such as iris implant surgery, carry severe risks including vision loss, glaucoma, and cataracts. These procedures have potential for serious complications.
Why Eyes Appear to Change Color
Many instances where eyes seem to change color are not due to actual physiological changes but rather how light interacts with the eye or how the eye is perceived. Different lighting conditions, such as natural sunlight versus artificial indoor lighting, can dramatically alter how eye color appears. This is especially true for lighter eye colors like blue or green, where light scattering plays a significant role in their perceived shade.
The size of the pupil can also influence perceived eye color. When the pupil dilates in dim light or due to emotional responses, the iris appears smaller, which can make the eye color seem different. Conversely, a constricted pupil in bright light can make the iris appear more prominent and its color more intense.
Surrounding colors, such as those from clothing, makeup, or environmental elements, can create an optical illusion, making the eyes seem to shift in hue. While emotions themselves do not change eye color, physiological responses associated with strong emotions, like pupil dilation or blood vessel changes, can contribute to a perceived shift.
Seeking Medical Advice for Eye Color Changes
An unexplained or sudden change in eye color warrants a consultation with an eye care professional. While some changes, like those in infancy, are natural, others can indicate an underlying health issue. A new or noticeable difference in color between the two eyes (heterochromia) could be a symptom of a medical condition.
It is important to seek medical attention if eye color changes are accompanied by other symptoms such as pain, redness, blurred vision, or light sensitivity. An ophthalmologist can determine whether the change is benign or a sign of a condition requiring treatment, ensuring eye health and preserving vision.