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Brown eye-color provides more UV protection than lighter eye-colors, and are dominant in regions where year-round exposure to the sun is greater.

Eye-color represents a fascinating story of evolution.

The development of some eye diseases are considered at least partly the result of cumulative life-time exposure of the eyes to the sun.

Ultraviolet rays of the sun are damaging to the eyes

Ultraviolet (UV) light is made up of invisible rays emitted by the sun. UVB and UVA are the two UV rays of concern. UVB rays burn the skin and besides causing wrinkles around the eyes, can easily damage the eyes and contribute to the development of eye diseases such as cataracts and age-related macular degeneration. Studies show that UV exposure can contribute to a number of additional ocular complications, including pterygium (an abnormal growth on the eye’s surface) and eye cancer. People with blue eyes (less pigmented) are somewhat more likely to develop melanoma of the eye than are people with brown eyes (see here).

Protect your eyes from the sun

Although the pigmentation of our eyes provides some natural protection, shielding the eyes from the damaging effects of the UV rays is important, and the lighter your eyes, all the more so. It has also been suggested that sunlamp exposure may be a risk factor similar to the UV rays of the sun.

The most common eye color in the world is brown

In humans, the greatest diversity of eye color is found among individuals of European descent. Some eye colors are so mixed that they are difficult to classify in a simple manner. The most common eye color in the world is brown, which in many populations is the only iris color present. The second most common eye color is blue or grey, while green eye color is rarest, observed in only 1-2% of people in the world.

Brown eyes are dominant in regions where year-round exposure to the sun is greater

Light-colored eyes, i.e. those that are not brown in color, are most frequently found in people from Northern Europe, where there is less exposure to UV-radiation. In contrast, brown eye color tends to be dominant in regions where year-round exposure to sunlight is greater. Those with lighter iris colors have been found to have a higher prevalence of age-related macular degeneration than those with darker iris color and an increased risk of uveal melanoma has been found in those with blue, green, or grey iris colors.

Lighter eyes had an evolutionary advantage in places with low levels of sunlight exposure

Lighter pigmentation is however thought to have enabled individuals to maintain necessary levels of UV-dependent Vitamin D production in places with low levels of UV radiation exposure, for example in Northern European countries. A sufficient supply of Vitamin D is needed so that a person can absorb an adequate amount of calcium from food, which in turn is a key chemical for many cellular processes and bone formation. Another possible explanation for the rapid increase of blue eye color in some past populations is sexual selection.

The high frequency of blue-eyed individuals in Northern Europe is consistent with the notion that there was strong positive selection for lightly pigmented skin and light colored eyes

It is not yet clear when the mutations (i.e. genetic variants) responsible for blue eye color first appeared. However, it is likely that this occurred in a population living somewhere close to Europe, possibly in the Near-East or Northwest of the Black Sea region. The high frequency of blue-eyed individuals in Northern Europe is consistent with the notion that there was strong positive selection for lightly pigmented skin, eyes and hair in the ancestors of these populations.

More information

For more information about eye-color, sunlight and eye diseases, talk to your doctor and visit the following web-sites:

• Eye Color Genetics by Barry Starr
• Eye Care America
• What Color Eyes Would Your Children Have?, by the TECH Museum of Innovation
• Wikipedia article on Eye-Color
• The National Eye-Institute
• Understanding UVA and UVB, from The Skin Cancer Foundation

This content was last reviewed on February 09, 2010.

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