Question: What causes the iris of the eye to change color? For most of my life, my iris color in each eye was dark brown. When I was in my 50s, the color began to lighten. I'm now 62, and the iris color is hazel, a mix of brown and green. Also, my father's eyes slowly changed from hazel to pale blue by the time he was in his 70s.
Answer: The color of our eyes is based on the number and color of pigment granules (melanin) in our iris. These granules range in color from nearly colorless to dark brown. The darker the pigment, the darker the eye color is. The fewer the granules, the lighter the eye color is. Babies are typically born with blue eyes due to a minimal amount of melanin pigment in the iris at birth. From 10 to 15 percent of the Caucasian population will see a change in their eye color as they age. In the case of you and your father, the eye color changed due either to a gradual decrease in the number of pigment granules in the iris or to a degradation of the granules. Your father had a greater loss of pigmented granules, and this caused his eyes to appear blue later in life. There's a small chance that an eye disease like pigmentary glaucoma, Horner's syndrome, or Fuchs heterochromic iridocyclitis could cause eye color changes, but these tend to be associated with a more rapid change in eye color. An eye doctor could determine if such an eye disease exists.