NEW YORK: Success lies in the colour of your eyes, and those with blue ones are likely to achieve more in life than their peers as they tend to study more effectively and perform better in exams, says a study conducted by US scientists. The study did not mention anything about people with black irises.

The tests showed that brown-eyed people had faster reaction time, but those with lighter eyes appeared to be better strategic thinkers.

Brown-eyed people succeeded in activities such as football and hockey, but lighter-eyed participants proved to be more successful in activities that required skills in time structuring and planning such as golf, cross-country running and studying for exams, the scientists said.

Louisville University professor Joanna Rowe, who conducted the tests, said the results suggested an unexplored link between eye colour and academic achievement. "It is just observed, rather than explained," she said. "There's no scientific answer yet."

Bedfordshire University senior psychology lecturer Tony Fallone, who has also studied eye colour, believed it should be taken more seriously as an indicator of personality and ability.

Blue-eyed academic successes include Stephen Hawking and Marie Curie who twice won the Nobel prize, for physics and chemistry.

Blue eyes contain low amounts of melanin within the iris stroma. The type of melanin present is eumelanin. People with blue eyes are relatively common throughout Europe and other areas with populations of European descent, such as Canada, the US, Australia and some countries of the Middle East. Afghanistan and Iran also have somewhat uncommon occurrences of blue-eyed people.

There are also populations in northern India and Pakistan that have naturally occurring blue eyes, although this is extremely rare. Throughout the rest of the world they are relatively rare. Around eight per cent of the world's population has blue eyes.

As melanin production generally increases during the first few years of life (especially if exposed to the Sun), the blue eyes of some babies may darken as they get older.

In the case of blue-green eyes, they must be more blue than green to be considered blue. Aqua blue is a good example of eyes that are more blue than green. Among Asians the predominant colour of the eyes is black.