By Aimee Lewis, CNN

(CNN) -- Look left, look right. Look up, look down.

Whatever you may observe, whatever you may come across, you won't spot the things that Dr. Sherylle Calder can see.

The South African has been described as the most successful person in sport. She is often called a visionary, a pioneer.

She is the go-to coach for many of the world's elite athletes, standing alone in her field, an expert in an area that is often overlooked; improving what is regularly abused, even by those at the peak of their sporting powers.

Speed, strength, mental fortitude -- the key components to sporting greatness. But it is incremental improvements, often called marginal gains, which can separate the great from the good, be the difference between winning and losing.

For Calder, the eyes are the missing piece of the sporting jigsaw, a weakness that can become a strength.

Specializing in eye-hand, foot and body co-ordination, she is the woman charged with helping athletes see better, anticipate quicker.

It is not about having impeccable eyesight, she says. Her work is not sight-related, but is based on improving the visual motor system and decision making.

"The eyes have to move effectively, just like the body," Calder, the first sports scientist to be awarded a doctorate in visual performance, tells CNN Sport.

"Most people believe we are born with the system we have, but you can train the eyes, the brain and the body to perform better.

"We warm up the rest of the body, but about 80 to 90% of the information that you base a decision on comes from the eyes and it's the only system we put by the wayside."

The creme de la creme of world sport

Calder currently works with England's rugby union team, Formula One driver Valtteri Bottas and Kenny Stills, the Miami Dolphins wide receiver who has thanked her for adding "the edge" to his game.

The sports scientist was labeled as the "secret" to Ernie Els' victory at the British Open in 2012 after the South African golfer had sought her help in the months leading up to his victory in England.

The list of Calder's past clients is exhaustive. It is the crème de la crème of the sporting world: the All Blacks, Australia's cricket team, English Premier League side Tottenham Hotspur, the Prada Yachting team and French Ligue One side AS Monaco.

She can also lay claim to having won back-to-back Rugby World Cups with different nations, first with England in 2003 and South Africa four years later. Former Springboks winger Bryan Habana thanked her for making his eyes as quick as his feet.

Calder says that the winger's intercepted try against Argentina in the semifinals of the 2007 Rugby World Cup won the Springboks the tournament and was proof that, in subtle ways, visual training impacted the performance.

"Elite athletes think they're good at everything. They think they're perfect, especially when it comes to visual motor skill level," Calder says, smiling.

"We show them they have strengths and weaknesses and it's really exciting for us to make every player a little bit better."

The digital decline

The professional athlete of today lives in a different era to the stars who were idolized in years gone by. The digital age, the habitual use of social media, the soaking up of information from a small screen, has created new problems.

Calder says she has scientific evidence which suggests that skills and visual awareness, such as the processing of information, concentration, co-ordination, to name a few, are in decline.

Those in the "better-in-my-day" camp, bemoaning that today's ball players haven't the flair or the skill of their predecessors, may have been on to something after all.

Sport's best of the best, as are the rest of us, are suffering from digital deterioration courtesy of our irresistible digital devices.

"We've found in the last five to six years there's been an overall decline in the visual motor skill level of elite players," she says.

"The eyes were never designed to work on small devices and, because of that, we're really abusing how we should be using our eyes.

"When you look at your phone there is limited eye movements happening and everything is pretty static.

"When we're on digital devices we really have limited attention span so our ability to concentrate and pay attention to a specific task is deteriorating.

"Any system you don't use effectively or abuse deteriorates so we think that every person in the world should be doing some form of eye/brain training to prevent the decline of the system.

"Looking up to the furthest point you can focus on helps, and therefore looking up now and again would be a start. However you need to specifically train that system."

'We're trying to change behavior'

Calder admits that she sees elite athletes on their smartphones or iPads "all the time."

Over the next three years with England's rugby union squad, as the country builds to the 2019 Rugby World Cup, she will attempt to alter habits.

"We're trying to change behavior and any behavior-change takes time," she says. "By the time we get to the World Cup we'll be ready to perform."

Players have been told not to use their devices on match day, while they have been asked to reduce their digital consumption during training weeks.

What will the long-term impact of this digital decline have on sporting performance? Particular sports won't suffer more than others because, says Calder, the decline is across the board.

"People don't notice because everyone's doing the same," she says.

"In 10 years' time the situation might be better, I'm sure it's going to evolve. The awareness of the problem is starting to surface.

"You have to find a way of training the visual motor system -- that's really the only thing you can do."

Training the eyes at the gym

It is winter in England and Calder is overseeing her first training sessions as England's visual awareness coach, an appointment made by head coach Eddie Jones this January. The Six Nations, which England will go on to win undefeated, is just weeks away.

During her initial on-field exercises, she notices one player in particular is poor at catching the ball whenever it falls from on high.

Here is one his country's best, a player of considerable talents, but his ability to judge distance and space is not up to standard.

"He was really bad at judging where the ball was in space," Calder recalls.

"If out of 10 balls you always drop three, it puts pressure on you as a player.

"If you can't catch high balls, there's a tendency to think that's just the way it is, but we show them it's something that can be improved.

"Once it is improved they begin to refine their skill and can move to the next level -- they can also improve the skill of having more time on the ball. The earlier you see, the more time you have to make a decision. That's a trainable skill."

Calder's role with England, the world's second-best side, for the next 12 months is to improve how the backs -- the team's creatives, the speedsters -- see the game.

Next year she will work with the remaining squad members, bringing the granite-jawed forwards onto her roster.

This year she has twice flown from her South African base to Pennyhill Park, a luxurious complex west of London where Jones and his men hold training camps, and will work in person with the squad again this autumn.

In her absence, the players are told to go to the gym -- Calder's EyeGym, an online program developed over the last 20 years which contains 60 varieties of drills, each adapted to the individual.

The EyeGym, says Calder, is an antidote to the visual system's digital decline and the beauty of the software is that this in-demand coach can monitor results wherever in the world she may be. Players can also train anywhere in the world.

The EyeGym is akin to a computer game, but based on science -- objects whizz up and down and across the screen, testing the user's reactions, memory, coordination, peripheral and special awareness.

It is the EyeGym that F1 driver Bottas uses before he gets into an F1 car, training the eyes on a specially-devised warm-up drill.

"If you make a mistake in F1 it is a lot more crucial than in, for instance, a rugby game so we make sure he's ready to perform by getting the visual system fit and ready to respond to anything happening around him," explains Calder.

It is the EyeGym which has also helped stop the aforementioned rugby union player, who Calder prefers not to name, from wobbling under the high ball.

"He's been one of our greatest trainers," says Calder.

"We're still working with him. It's like a fitness skill. We train these skills and we get them up to standard and we top it up all the time. Once you get a skill up to standard there's always something else you have to work on.

"If we make each player on the field make one better decision per match, that could be 22 better decisions in the game.

"Sometimes when the players are tired and fatigued we put them on the training system because that's often when you have to perform.

"The eyes and the brain get tired, just as the body does. Often with elite players we find that physically they're in good shape, but if they lose concentration they make mistakes -- not because they technically can't do it but the visual system is giving them information either too slowly or inaccurately.

"The eyes get tired and they start to misjudge. It's not always because you're physically tired."

The A-star students, such as former England outside-half Jonny Wilkinson, whom Calder describes as "one of the greatest trainers I've ever worked with," will do extra sessions.

Few, Calder understands, possess Wilkinson's relentless drive for self-improvement and so demands a minimum of 10-minute sessions three times a week.

Seeing things differently

Calder first noticed she saw things differently while playing field hockey in Europe during her country's sporting isolation in the apartheid era.

"People would ask 'how do you do that?' 'how do you see that?' I presumed they all saw what I saw," says Calder, describing how she would be first to the ball even when she was not the fittest or the quickest on the pitch.

"Most people said I was born with those skills and I'd say I wasn't, that I actually trained them by being inquisitive and testing out things."

After 50 Tests for South Africa she retired in 1996 to start her research into how the eyes affect performance, working with athletes from different sports and various countries.

"I decided to take the way I trained and put it into a training program," she says. "I proved in my research that if you train your eyes in a certain way and you train on the field in a certain way, if you combine the two you can improve performance.

"As I've tested elite players, I've asked certain players to tell me about how they grew up and I've found that skills in different countries are different.

"The countries where athletes grew up playing outside had better skills in certain components, but were lacking in other components.

"If you've grown up playing outside, you've got better coordination, better peripheral, awareness of depth, where you should be reaching, eye-hand, eye-foot co-ordination. Just decision-making really.

"People don't play outside anymore. I think kids should be playing outside, climbing trees, jumping over fences, walking on walls, falling off, getting back on, learning to do it again."

Calder's influence is not solely fixed on judging where a ball is going to be or the line and length of a putt. She trains a vast section of society, from business people to students and schoolchildren.

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"We work with everyone, normal guys on the streets, a lot of kids, a lot of older people on memory skills. We work with big corporates on productivity because with concentration skills declining the productivity has also come down.

"If you use your eyes you should be training them, you should be keeping them fit. It applies to everyone."