02 April 2007

Sports Vision Training

An expert guide to improving performance by training the eyes.

Brian Ariel

VERGENCE (also known as Fusion Flexibility) is the ability to rapidly and accurately fuse the two images from the eyes into one image when focussing from far to near (convergence) and vice-versa (divergence). The eyes work as a team to maintain this 'oneness' in all directions of gaze. Deficits in this ability, a slowness or a slackness in locking on to an object, can lead to double vision and poor timing. An example of vergence where speed is not essential is of a golfer looking at the ball and then at the hole on the putting green and repeating this procedure several times before hitting the ball. Speed of vergence is necessary in ice hockey where a player has to 'lock on' to a fast-moving puck.

Prism Flippers

This device is like two fronts of a pair of spectacles holding prismatic lenses. One set tends to pull the eyes in and the other pair tends to do the opposite. The training occurs when the subject makes an effort to overcome the deliberate double vision that the prisms cause. The number of times (flips) the subject sees singly when alternate pairs of lenses are put before his eyes in a given period is recorded. Practice increases this speed of vergence. A drawback to this method is that the subject , in order to impress the sports vision trainer (SVT), may not be completely honest. If a sportsperson has only one functioning eye or has a certain type of squint (strabismus), then eye teaming cannot occur and vergence difficulties cannot exist. There are sports when being monocular (one-eyed) has definite advantages.

ACCOMMODATION (also known as Focus Flexibility) is the ability to change focus from near to far or vice-versa. At rest, the eye is focussed at one metre so that focussing both nearer and further than one metre involves an accommodative effort. In most sports it is preferable to be able to focus clearly and quickly on the object of regard. It can be a moving object like a football or a stationary object like the fore and rear sights of a rifle while shooting. Orienteers, who have to read a map while running, need good speeds of accommodation. Deficits in this ability can lead to difficulty in timing and accuracy.

Plus/Minus Lens Flippers

These are similar in construction to the prism flippers described above. To measure this parameter of vision, the subject is instructed to focus on a suitable line of letters at an appropriate distance through lenses (low magnifying lenses) which force the eyes to relax their accommodation, and then through the other set of lenses (low minifying lenses) which do the opposite, forcing a contraction of accommodation. The number of times (or flips) clarity is achieved in a given period is recorded. The disadvantage of this method is the same as that described for vergence measurement.

Bart Charts

These are two identical letter and number charts. One is of reduced size to be used at a closer distance. They are aligned to simulate the sporting situation and the subject has to call out alternative letters or numbers, quickly focussing from one chart to the other. Each effort is timed and recorded to check progress. The SVT watches the subject's eyes to ensure that the subject doesn't re-focus and isn't just remembering a digit in advance from the easier chart.

A lot of the parameters just discussed are inextricably linked, especially accommodation and vergence and, to a lesser extent, spatial location (discussed last month).

SPEED OF RECOGNITION (also known as Visual Search) is the ability to recognise and abstract relevant information at a glance. A study of badminton players demonstrated that the better players could, even with limited visual clues, predict the position of the shuttlecock. They did this by making better and quicker use of the limited clues to extract relevant information only. When recreational players were given the same visual clues, they could not predict the shot. In fact, even with added clues they could not predict as well as the elite players. The novices were poor at recognising the essential information, and spent too much time scanning redundant information.

The Tachistoscope

This instrument is a manual projector with variable shutter speeds. It is used with slides of letters, numbers and sporting situations. To train speed of recognition, the shutter speed is increased in increments, from 1/10th to 1/100th second, while the subject tries to maintain the same level of search information as at the lower speeds. The SVT instructs the subject as to the information required before each slide is projected on to the screen. This might be to recall an array of numbers or to predict the trajectory of a ball. Practising this skill increases the speed and span of recognition.

VISUAL MEMORY is the facility to remember visual information, often at a glance. There are several examples in sport where this facility is highly beneficial - for instance:
motor sport: memorising the circuit with all its contours and bends helps in avoiding accidents;
snooker: as the cue ball is addressed, the elite player has a complete picture in his head of all the balls in play. This will not only allow him to place the cue ball in a good position for his next shot but also reduce the likelihood of leaving his opponent any advantage;
cricket: the batsman should have the field placings in his memory, so that he doesn't hit the ball to the fielders.

Wayne Saccadic Fixator

The programme used on this instrument (which was described last time) to train and measure this parameter is similar to the Simon Game played by children. To begin the test, a light on the panel comes on, and when the subject touches it, it goes off. Next, the same light comes on again plus, a second later, another light. This time the lights have to be extinguished in the same order that they appeared. After each successful attempt, which is displayed numerically, another light is added to increase the memory span. Failure to follow the correct sequence is indicated by an auditory signal. The delay in time between successive lights can be increased to add difficulty. By concentrating, the memory span can be seen to expand.

OCULAR DOMINANCE. A dominant or referential eye is the one which is sighted towards a target. It does not have to be the eye with the better vision, nor does it have to be allied to the dominant hand or foot. Sometimes there is no definite dominance, a condition which is often seen among dyslexics, and this can result in visual problems.

It is unwise to change a person's ocular dominance, although certain occasions may necessitate this rather drastic action. The dominant eye for distance vision (six metres upwards) may not be the same eye for intermediate or near vision (2/3 metre). If no definite dominance exists, then blurring or occluding one eye is of help.

There are a few ways to find out which eye is the dominant one:

  1. Ask the subject to make a small triangle using just the thumbs and forefingers of both hands, right on top of left, and then stretch the arms fully in front of his face while lining up to one of the observer's eyes. It is easy for the observer to see which eye the subject is using preferentially. This procedure should then be repeated twice more, and then another three times with the left hand on top of the right.
  2. Ask the subject to look through a tube at the observer. The subject will instinctively look through the tube with the dominant eye. Repeat the exercise half a dozen times.
  3. Ask the subject o stretch his arm straight ahead and point his finger at a small object. Then instruct him to close one eye and ask whether is finger is in line with the object. Repeat this exercise when closing the other eye. Looking with the non-dominant eye will result in a marked non-alignment. Once again, there should be a half a dozen attempts. It is most instructive to repeat the same routine at intermediate and near distances.
Cross dominance (or cross laterality) is where there is a right eye/left hand or left foot dominance or vice-versa. In sports where a side-on stance is required, his condition has definite advantages - for instance, batting in cricket. In a study of PGA players, measurements were made of the golfers' driving distances, and those who were cross dominant were also the longest hitters. If cross-dominant clay-pigeon shooters sight with their dominant eye, then there will be a mis-alignment in spotting the target. Partially blurring the offending dominant eye will aid accuracy.

Failing to have a dominant eye at a certain distance can cause inaccuracy in golf. A good example is a scratch golfer whose long and short putting were fine but at about eight feet he was constantly wayward. He had his dominance checked and at eight feet there was none. Instructing him to use only one eye solved the problem.

Contrary to popular belief, it is only when addressing a stationary ball that one has to keep one's eye on it all the time (it is impossible to track a fast-moving ball continuously). If a golfer is asked to close his dominant eye while swinging his club, he may well not be able to see the ball. However, if his stance is altered, even slightly, it may ensure that his dominant eye is definitely kept on the ball with the result that he will be able to hit further and more accurately.

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