People might ask you where you got those baby blues. Eye color is a phenotype, or a visible result of genetic coding. Complex genetic pairings determine what eye color you have, and even brown-eyed parents can have a blue-eyed child. According to the U.S. National Library of Medicine, pigment cells in the iris produce two types of melanin, which help determine eye color. Dark-eyed people have a lot of eumelanin, and light-eyed people have a lot of pheomelanin. Brown eyes are the most common color. Eye color does not usually change over a person's life span, but under certain circumstances, it can.
1. Environment and Age
Perceived changes in eye color are often a result of differing light conditions. Direct sunlight causes pupils to constrict. Light-colored eyes appear brighter as the dark pupil gets smaller. Pupils enlarge in low light conditions making the eye appear darker. The color of ambient light also influences how you perceive eye color. Objects look warmer bathed in the golden light of sunset. Cool-hued reflections from new-fallen snow add a blue tint to objects. Irises are partially transparent, and they can appear to change color in different surroundings. The three main pigments that determine eye color are brown, yellow and blue. Most light-skinned babies are born with very little melanin, or eye pigmentation, at birth. Pigmentation develops along with the child, so eye color can change, along with hair coloring, as a child grows past adolescence into early adulthood.
2. Outside Causes
Eye trauma, such as a blow to the eye, can affect pigmentation in the iris. Blue or other light-colored eyes might develop brown patches where the injury occurred. Some prescription eyedrops, used to treat glaucoma, have the side effect of darkening iris color. Blue eyes deepen; gray eyes or green eyes can turn brown. The pigmentation changes are usually permanent. Color contact lenses can change light-colored eyes into a more vivid hue or even turn brown eyes into turquoise or green colors. A friend whose eye color seems to change as often as the weather likely has a selection of colored contact lenses at home.
Irises changing to a grayish hue--accompanied by blurred vision--may be a symptom of uveitis--an irritation or inflammation of the eye. The Mayo Clinic says yellowing of the white of the eye can be indications of liver disease because of conditions such as malaria or hepatitis. The inability of a person suffering from Wilson's disease to properly absorb copper results in a characteristic rusty yellow ring around the iris. The rings, known as Kayser-Fleischer rings, result from an accumulation of copper in the iris, according to the British Journal of Ophthalmology. Cataracts can cloud the lens of the eye and can make the center of the eye appear gray-blue.