Hazel eyes: What determines hazel eye color?

How eye color is determined

Most of us were taught in high school science class that we inherit our eye color from our parents, and that brown eye color is dominant and blue is recessive. That would mean that two parents with blue eyes cannot have a child with brown eyes because neither parent carries the dominant form of the gene for brown eyes.

But it turns out the story is more complicated than that.

Recent research has shown that up to 16 genes (not just one or two) may influence eye color, which makes predicting eye color much more difficult.

Due to variations in the interaction and expression of multiple genes, it's hard to say for sure what color a child's eyes will be based on the color of his or her parents' eyes.

For example, we now know it's possible for two blue-eyed parents to have a child with brown eyes — something the old model of eye color inheritance would have deemed impossible.

Also, eye color can change dramatically in the first few years of life. Many white, non-Hispanic babies are born with blue eyes and then develop brown, green or hazel eyes in childhood.

This phenomenon has little to do with genetics, but it does help explain where hazel eyes come from.

What causes hazel eyes?

The pigmented structure inside the eye that surrounds the pupil and gives eyes their color is called the iris. The pigment responsible for eye color is called melanin, which also affects skin color.

The reason many white, non-Hispanic babies are born with blue eyes is that they don't have the full amount of melanin present in their irises at birth. In the first few years of life, more melanin may accumulate in the iris, causing blue eyes to turn green, hazel or brown.

Babies whose eyes turn from blue to brown develop significant amounts of melanin. Those who end up with green eyes or hazel eyes develop a little less.

Babies of African-American, Hispanic and Asian ethnicities are usually born with dark eyes that stay brown throughout life. This is because these individuals naturally have more melanin in their eyes and skin.

Light absorption and scattering

There are no blue, green or hazel pigments in the eye. Eyes merely have different amounts of melanin, which is a dark brown pigment.

So how can a dark brown pigment create blue, green or hazel eyes? This is possible because of two processes:

1. Melanin in the iris absorbs different wavelengths of light entering the eye.

2. Light is scattered and reflected by the iris, and some wavelengths (colors) scatter more easily than others.

Eyes with high concentrations of melanin absorb more light entering the eye, so less is scattered and reflected back from the iris. The result is a brown eye color.

In eyes with lower concentrations of melanin, less light is absorbed, and more is scattered and reflected by the iris.

Since light rays with shorter wavelengths (blue and green light) scatter more easily than light rays with longer wavelengths (red light), eyes with less light-absorbing melanin appear green or hazel, and eyes with low concentrations of melanin appear blue.

Also, the distribution of melanin can vary in different parts of the iris, causing hazel eyes to appear light brown near the pupil and more green in the periphery of the iris.

Hazel eyes are a work of art

Hazel eye color is both complex and magnificent, since its specific features are determined by many factors:

• The amount and distribution of melanin in the iris.

• How the scattering of light by the iris and pigment molecules affects color.

• How the perception of eye color is influenced by lighting and the color of our clothing and surroundings.

Just as it takes many strokes of the artist's brush to produce a masterpiece, hazel eyes involve the dynamics of several elements to create the unique work of art that's represented in every hazel eye.

If you wear eyeglasses, consider lenses with an anti-reflective coating to eliminate distracting reflections in your glasses and allow others to see the beauty of your hazel eye color.

Changing your eye color with hazel contacts

If your eyes aren't naturally hazel, but you've always wanted them to be, you can achieve your wish with color contact lenses.

They won't actually change your eye color, of course, just the appearance of it.

Color contact lenses are available in many colors, so you can choose from a spectrum that includes every shade from light hazel to dark hazel.

But it's not simply a matter of choosing a lens color you like; the natural color of your eyes has a role in determining which lenses will look best.

If you have very light eyes, color contacts with an "enhancement tint" might be a good choice. These lenses have a translucent color that lets some of your natural color show through — to make your light blue eyes a deeper blue, for example.

If your eyes are light enough, you might achieve the hazel eye color you want with an enhancement tint.

More likely, you'll need lenses with an opaque tint to achieve a hazel eye color. These lenses are designed to mask your natural eye color with the color you desire. These lenses work well if you have dark brown eyes and want to give them a lighter appearance, including hazel.

An eye care professional can show you various colors and help you make the right choice.

Remember, hazel contact lenses require a contact lens prescription. So if you don't already wear contacts, you'll need an eye exam and a prescription before getting them — even if you have perfect vision without corrective lenses.

SEE RELATED: Eye color change surgery