Honing the sight can be as vital to an athlete as toning the body. Simon Usborne reports

Since when did an eye test require a stopwatch? My task, Miranda the optometrist-cum-timekeeper has told me, is to flit my vision between two rings of numbers – one at arm's length and the other several feet away – and read them alternately in a clockwise direction. I have to do four laps as quickly as possible (without tripping over my words or showering poor Miranda in spittle) and then try to beat my personal best.

It seems appropriate that a "sports specific" eye test should feel like such hard work. As I force my eyes to focus and refocus more than twice a second (failing to suppress competitive urges, I get my time down to a respectable 23 seconds), I can feel the tiny muscles in my eye beginning to ache. Is that a bead of sweat forming on my brow?

It might look (and feel) like an even lower-budget version of The Krypton Factor's mental agility round, but eye tests like these could mean the difference between gold medals and red faces for Team GB at the Beijing Olympics. And, for part-timers like me, Miranda says testing and training the seven little muscles that control the eye could improve performance on the tennis court, football field or cricket pitch.

Our eyes contain what optometrists believe to be some of the most neglected muscles in our bodies. Athletes invest so much in honing and sculpting their quads, pecs and abs, but how many could even identify their medial rectus or superior and inferior obliques? (If you can't either, they are, the muscles that pull the eye towards the nose, and allow you to look up and down.)

David Ruston, an optometrist with Johnson & Johnson Vision Care, which is giving eye training to some of Great Britain's Olympic hopefuls, was shocked at the level of eye care he found when he started working with the team. "I remember the British Olympic Association saying that there was no requirement for Olympic athletes to have their eyes checked, whereas there was a requirement to have a dental examination," he says.

A survey of competitors at the 1992 Olympics and the 1994 Winter Games found that only half had received an eye exam, while a quarter had admitted to visual difficulties. A more recent study found that even among elite athletes, 40 per cent of them suffered visual problems that could be easily corrected. Ruston adds: "I know athletes going through our programme who have a level of vision that would barely get them through a driving test, and yet they're performing at the highest level."

The Commonwealth heptathlon champion Kelly Sotherton, who won bronze medals at the last World Championships and Olympic Games, is one athlete hoping to climb higher up the podium thanks to eye treatment. Ruston examined Sotherton at Johnson & Johnson's clinic in Prague: "She told us that in javelin, which has been her weakest event, she struggled to focus on its point when throwing," he says. What's more, Sotherton would clip hurdles because she couldn't judge distance to the millimetre-perfect level required for an event where milliseconds count. "Kelly's problem was poor binocular vision," Ruston explains. "Our eyes are meant to work as one, giving us stereoscopic vision, but that doesn't always happen. It's something you're not aware of until you realise how much better things could be."

To tune up Sotherton's eyes, Ruston prescribed a series of exercises, including one that uses something called the Brock string. By getting Kelly to look at coloured beads along a piece of string held out from her nose, and to describe how and where the string appeared to split into two, Ruston could train the athlete's eyes to work in perfect unison. Improvement soon followed. "Kelly now says she doesn't tip hurdles so much and feels better on javelin," Ruston says.

Another Olympic hopeful receiving treatment is Gail Emms, who, with her badminton doubles partner, Nathan Robertson, kept viewers on the edges of their seats when the pair narrowly missed out on mixed-doubles gold in Athens. "The guys smash at over 200mph and in mixed doubles they're aiming at my head," Emms says. "I not only have to react to the shock of it coming at me, but have to play a shot that puts me in a good position. Vision is absolutely crucial."

First Emms, 30, and Robertson were given eye tests – Emms's first since childhood. "I've always thought I had perfect eyesight but I was paranoid something would come up," she says. Fortunately, her vision was better than Sotherton's, but it wasn't perfect. Ruston found that when Emms looked up (over the net, for example) her eyes moved slightly away from each other, potentially affecting the way she could see speeding shuttlecocks.

Emms now does exercises three times a week, including one designed to improve reactions. Using specially designed software supplied by Ruston, she has to watch her computer screen as small letters facing in different directions pop up and move around. Emms has to hit the correct arrow button on her keyboard as soon as her eyes find the letter and determine its direction. Like a computer game, it gets harder with every level. "I've reached level 20 out of 20 and now use it to keep training the muscles," Emms says.

Emms and Sotherton aren't the only athletes to have benefited from eye training, which in the past decade or so has become as crucial a part of elite sport as psychology. Sports vision first took hold in the United States in the Eighties, where it became popular with baseball teams. It soon pitched across the pond and, in the UK, specialist eye consultants were employed by the Subaru World Rally team and the Scottish hockey team. In 2003, the expertise of South African optometrist, Dr Sherylle Calder, was credited with helping the England rugby team to victory in the World Cup final against South Africa. Calder then switched her allegiance back to her home nation, helping South Africa to get revenge on England in last year's World Cup final.

But, according to David Ruston, you don't have to be a pro to benefit from eye exercises, which is why Miranda is giving me the once-over at Expressive Eyes in Wimbledon village, south-west London. She's among more than 100 optometrists around the UK who, since last December, have been offering a high-street version of Johnson & Johnson's pro sports eye test.

It takes about 45 minutes for Miranda to put me through my paces. The speed, or "dynamic fixation", test is one of six, during which Miranda also gets me to read from the Snellen chart (the traditional letters of decreasing sizes) and takes a photo of my retina to check for defects. I come out of the ordeal feeling as if I might like a snooze to let my eyes recover, but with a clean bill of health. "Certainly for the next 10 years you shouldn't need any correction," Miranda assures me.

For someone for whom competition amounts to petty races in the gym pool or on the cycle commute, it hardly matters whether my eyes are merely fine or perfect. For Gail Emms, who will be facing those lightning-fast Olympic smashes in a matter of weeks, it's rather more important than that. "When we play our best we're the best in the world," she says. "It's just getting our game together and being in perfect shape – and that includes our eyes."

Five ways to improve your sports vision

The eye loves to jump from one thing to another. If you work in an office, look to the other side of the room or out the window every 20 minutes.

In most sports, your eyes need to be able to dart around readily in space. In a darkened room, flick a pen torch around and attempt to follow it.

Stand in front of a mirror and move your head around while maintaining eye contact. This is a simple way to exercise all six muscles that move the eyeball inside the socket.

To improve peripheral vision, sit at your desk and keep your focus on something ahead of you, such as a screen. At the same time, try to increase your awareness of what is happening around you.

Always protect your eyes in sports where there is a danger of being struck, such as squash, and from sunlight, by wearing sunglasses or UV-blocking contact lenses. The sun is most harmful when low in the sky.