"It helps your eyes relax instead of squinting all the time," said Danny Graves of the Cincinnati Reds baseball team, who has also been testing the lenses. "And that helps relax the rest of your body."
Graves also discovered another benefit - they can intimidate opponents. "They make you look kind of evil," he said. "Other players look at you like you're possessed."
However, leading optometrists today warned that use of the lenses would need to be tightly controlled. "Hygiene would be a worry here," said Judith Morris, a contact lens expert at City University.
"If you use these lenses for one match a week, then store them in a case, there could be problems. And obviously they would absolutely have to be fitted professionally."
Tony Chipote, a marketing field manager for Nike, said: "We want our athletes to continue to see their game better and better for longer and longer. As soon as you start to lose your eyesight, the rest of your body will start to suffer."
Nike has also signed up tennis star Roger Federer and golfer Justin Leonard to test the lenses. It claims that while the red lenses are ideal for fast-moving sports such as football, grey lenses are the key to golfers being able to discern the lie of the land on a putting green.
