Why Do Some People's Eyes Change Color?

Eye pigment is stored in the stroma (connective tissue) of the iris.

The iris is the colored portion of the human eye. Eye color is determined by the amount of pigment found in the iris. Large amounts of pigment result in brown eyes, medium amounts result in greenish hues or middle-toned colors, small amounts of pigment give rise to blue eyes and no pigment usually reflects a state of albinism.

Non-pigmented Eyes at Birth

It is common to see a newborn baby born with non-pigmented (blue) eyes that later change in color. The cells that store melanin (pigment) within the eye, have not had enough time to create noticeable amounts of pigment in the iris, so the eyes appear blue. By the time a child reaches age six, her eye color will be established based on the amount of pigment that has accumulated over the past several years.

Change of Pigment with Age

After adolescence, and continuing through old age, human eyes may slowly change in color. Approximately 10 to 15 percent of (generally healthy) Caucasians experience either a lightening or darkening of eye color as they grow older.

Eye Diseases

A few examples of eye diseases that cause color changes are Horner's Syndrome, pigmentary glaucoma and Fuch's heterochromic iridocyclitis. A noticeable or sudden change in an adult's eye color can be an indication of a diseased eye.

References

• Stanford School of Medicine: Understanding Genetics
• Fisher Science Education: Eye Color Explained
• USA Today: Funny - You Can't Hide Those Lightening Eyes

Resources

• All About Vision: Eye Color