The Science Behind Eye Color

Eye color is determined by the pigmentation of the iris and the way light scatters within it. The variations in eye color arise from the combination of genetic factors and the interaction of different types of melanin.

Eye color is a polygenic trait, meaning multiple genes contribute to it. The two main genes are OCA2 and HERC2. Mutations or variations in these genes can lead to a spectrum of eye colors, from blue to brown.

The amount and type of melanin in the iris determine eye color. Eumelanin results in brown eyes, while less eumelanin leads to lighter colors like blue or green. Pheomelanin, another type of melanin, can also affect hue.

Blue and green eyes appear so due to Rayleigh scattering, the same phenomenon that makes the sky blue. Low melanin levels result in light scattering in the stroma, giving rise to blue or green eye colors.

Eye color can change in the first years of life as melanin levels increase. In some cases, eye color may also change due to disease or trauma affecting melanin production or iris structure.

Some people can have two different eye colors due to a condition known as heterochromia. It can be genetic or result from injury or disease.