Eye color is determined by the concentration of melanin within the iris, the colored, circular structure surrounding the pupil. Although this pigmentation is set early in life, the eye’s biological components undergo subtle, cumulative changes over decades. These age-related transformations in the iris and surrounding structures alter how light is absorbed, scattered, and reflected, leading to a noticeable shift in the eye’s apparent hue.
How the Iris’s Pigment Changes with Age
The iris color results from melanocytes producing and storing melanin pigment. Lighter eye colors, such as blue or green, possess less melanin, causing light to scatter across the iris stroma. With age, melanocytes can become unstable, leading to a gradual loss or redistribution of melanin granules within the iris tissue. This degradation is the primary mechanism behind the fading of eye color in older adults, particularly those with lighter shades. The reduction in pigment diminishes the overall color saturation, making the iris appear lighter or a muted gray-blue.
Conversely, in individuals with darker eyes, pigment may not be lost but instead become compacted or clumped. This accumulation of melanosome complexes can cause the color to appear darker or more mottled. This clumping can make a hazel eye appear more brown or introduce darker speckles, changing the overall impression of the iris color.
The Appearance of Color Change Due to Corneal Deposits
A separate, common phenomenon that creates the illusion of eye color change is Arcus Senilis, also known as corneal arcus. This condition presents as a white, light gray, or bluish ring around the outer edge of the cornea. The cornea is the clear layer in front of the iris, and the deposit affects its transparency.
The ring is composed of fatty substances, primarily cholesterol, that accumulate in the peripheral corneal tissue. As these deposits build up, they create an opaque boundary that partially obscures the iris. This ring visually alters the contrast between the iris and the surrounding area. The contrast alteration makes the iris color appear duller or lighter because the sharp border is interrupted by the opaque ring. Arcus senilis is a benign change that affects nearly all people over the age of 80.
Alterations in the Sclera
The appearance of the iris color is heavily influenced by the sclera, the white outer layer of the eyeball. As a person ages, the sclera loses its bright white appearance and takes on subtle color shifts that impact the perceived vibrancy of the iris. This discoloration results from changes in underlying blood vessels and the accumulation of pigment.
Specifically, the sclera tends to become slightly more dark, red, and yellow with advancing age. The increased yellowness is attributed to the accumulation of lipid deposits and pigmentary changes. Redness is often due to increased visibility of blood vessels in the conjunctiva, the thin membrane covering the sclera.
When the sclera is no longer white, the contrast ratio between the white part of the eye and the colored iris is significantly reduced. This lessened contrast makes the iris color appear less intense or saturated than it did against a brighter backdrop.