运动视觉的训练
Sports vision - How enhancing your vision can give you that extra edge in competition
Sports Vision (SV) is the branch of optometry concerned with vision and perception, evaluating and enhancing visual performance, and prescribing, where necessary, the most appropriate visual aids.
Anyone who has problems with vision while participating in sport would be well advised to consult an SV practitioner. Such problems may be recognised by a player who experiences any of the following: variations during play, loss of concentration, a dip in performance either early or late during play, performing worse during the day than at night, or vice versa.
Visual problems may be suspected by a coach when play is inconsistent, not up to potential or deteriorating over time, or the athlete is under mental or physical stress.
For example, an international rugby player was referred to me by the team’s coach, who thought the player’s game was not up to potential, with a falling off in performance as the game wore on. The player complained of tired eyes. After a thorough eye examination and SV screening it was found that the player, who wore spectacles only for office work and driving, needed specialised contact lenses to correct lenticular astigmatism and provide good visual acuity. Wearing these lenses for sport proved highly beneficial. Uncorrected astigmats often suffer with tired eyes, since the condition makes undue demands on the ocular system. The longer the game continues the more tiring it is for an uncorrected astigmat.
In other circumstances, visual problems revealed during SV screening may be solved by seemingly unrelated methods. My case files include examples of players whose play improved after making such simple adaptations as changing foot position (county badminton player), altering body position at the net (a county tennis player), adopting a different head position (recreational badminton player) and restricting unnecessary head movements (school goalkeepers).
However, not all vision problems can be solved so simply by means of either optical correction or simple changes in posture. Some sports practitioners need to practise certain visual tasks repeatedly to improve a weakness, such as eye-hand speed, for example. We call this work ‘sports vision training’.
The idea of sports vision as a separate discipline dates back more than a century to 1886, when Sears, Roebuck and Co offered the first sports spectacles for sale. Spectacles advocated for sport gave wide and uninterrupted fields of view and were fitted with ‘Salvoc’ safety lenses (until then only glass lenses had been available). The safer CR39 plastic lenses became commercially available in 1972. With the advent of the more impact-resistant polycarbonate lenses in the mid-1980s, sports spectacles were able to give better protection and misting up became less of a problem. This year, Trivex was introduced, offering even better visual and safety properties than polycarbonate.
Standards for eye protection vary according to individual sports. There are, for example, British Standards for surface swimming (BS 5883) and squash (BS 7930-1) and a European Norm (EN 967) for ice hockey.
After 1945, when contact lenses became more available, people in need of vision correction (technically known as ‘ametropes’) were able for the first time to participate in sports for which spectacles were unsuitable, or even illegal.
In the last 20 years refractive surgery (laser treatment mainly used to correct short sight) has had a major impact on sports vision, having been successfully used and endorsed by such household names as Frank Bruno, Nasser Hussein, Jonathan Edwards, Tiger Woods and Sharon Davies.
Everyone is constantly on the lookout for an ‘edge’ in sport and, since vision is extremely important (over 80% of perceptual input is visual) optometrists who are sports vision practitioners can help to provide that edge, particularly as research has shown that at many as 30% of sportsmen and women do not have a satisfactory vision correction or visual acuity(1).
Data from the 1992 Olympics revealed some interesting statistics:
* Only half of the competitors had ever had their eyes examined…
* … yet one in four admitted to visual difficulties.
Data from the Winter Games of 1994 revealed that:
* 58% of competitors rating vision important had never had an eye examination;
* 19.59% wore spectacles but only 3.2% used them for sport, compared with 94.3% of contact lens wearers;
* 12.5% had substandard acuity in one eye and 4.6% had substandard acuity in both eyes.
Any athlete with a visual difficulty may visit an optometrist, but sports vision is about much more than the standard sight test. With sports vision, the entire visual system comes into consideration.
SVA – for efficient vision in sport
In the 1970s the numbers of people participating in sport rose exponentially and SV, as a science-based offshoot of occupational vision, began in the USA at around the same time. In the UK, it is now estimated that almost half the population engages in some form of sport on a regular basis.
SV is now an important speciality in its own right, and various pieces of equipment have been developed to allow for the measurement and training of various vision faculties and parameters.
The aims and objects of the Sports Vision Association (SVA), founded in 1993 and now under the umbrella of the National Sports Medicine Institute, are, among others, to promote safe and efficient vision in sport, to optimise visual ability in sport and to promote education, training and research into SV.
SV assessments start with measurement of a wide variety of visual faculties. Many sports have objects, like a ball or basket, which appear larger than the standard bottom line on a chart, so that the standard quantitative visual acuity measures are less relevant than contrast sensitivity, which is a measure of quality of vision. Dirty or scratched lenses, windscreens and visors all reduce contrast sensitivity.
Of course, not all sports use the same visual faculties and not all players in team games would use the same ones. Therefore, a sports visual task analysis is an essential part of the assessment.
After a thorough clinical eye examination, the SV screening will focus on measuring only the visual parameters relevant to the sport in question. There is no need, for example, to measure the eye-hand speed of an outfield footballer!
Some of these measurable faculties/ parameters, the equipment used to measure them and a few examples of the sports where they are pre-eminent are listed in the table opposite.
Less easily measurable faculties include visual concentration and visualising, which are important for all sports.
Every sport involves many visual parameters. In tennis, for example, anticipation, speed of recognition, peripheral vision, visual and auditory reaction times are all important. Some parameters, such as central-peripheral awareness, are common to many sports. The good news is that all these faculties are capable of improvement – with training.
Some instruments used for sports vision training (SVT) are versatile in that they enable more than one parameter to be measured. The ‘saccadic fixator’ is especially versatile since it has about 100 programmes and can train about 10 parameters. Any deficits/weaknesses in one or more parameters can be identified after an SV screening, and almost all of those with room for improvement can be trained – preferably out of season and with the prior permission of a coach.
In the adult, ‘hard wiring’ of the nerve cells suggests that the time taken for the image on the retina in the eye to reach the visual cortex in the brain is fixed and cannot be improved with any form of training. (This is not the case with children during their ‘plasticity’ period.) SV practitioners do not take issue with that claim, but sports vision training attempts to make better use of the hard wiring already in place. SVT does not claim to change recreational players into world-beaters, but it does claim to improve their sporting performance and give an ‘edge’ to élite performers.
Commentators and pundits often speak of players’ wonderful ‘vision’ or ‘eye’ when describing people who clearly have a highly-tuned visual system. They see clearly and quickly, read only the essential cues and have the motor response to act and react quickly and accurately. These attributes are the very ones SVT seeks to enhance.
Most visual parameters are trainable, resulting in measurable improvement. However, there is a good deal of scepticism about whether improvements observed in the laboratory or consulting room are transferable to the area of play. The value of nutrition, weight training, psychology, rest etc is accepted with no real scientific proof of its efficacy, but SV (maybe because it is a new discipline) has its doubters and detractors.
Table 1: Visual faculties, equipment and relevant sports Visual faculty Measuring equipment Relevant sports
Dynamic vision Pegboard rotator Baseball hitters, cricket batsmen
Eye movements King-Devick charts
Saccadic fixator (SF) Squash, table tennis
Focusing speed Flipper lenses, Marsden ball Shooters, wicket keepers
Central-peripheral awareness (CPA) CPA trainer Basketball, volleyball
Eye-hand coordination/speed SF Football, rugby
Eye-body speed Re-Act coach Ice hockey, hockey
Eye-body balance SF with balance board Skiing, luge
Anticipation speed Bassin anticipation timer/SF Clay shooting, cycling
Visual memory SF Batting in cricket, show jumping
Auditory reaction & response time SF Sprinting, tennis
Visual reaction & response time SF/Acuvision Goalkeeping, hockey
Speed of recognition & visual search Tachistoscope Badminton, tennis
Ocular dominance Tube, outstretched arms Archery, golf
Contrast sensitivity (CS) CS charts Where light conditions vary during play
Colour vision Colour vision tests Team games
Stereopsis (binocular vision) Stereopsis tests Golf, lawn bowls
Spatial location Brock string Diving, hurdling
The multi-factorial nature of sports performance makes it complex to study. For this reason, well-constructed controlled trials are essential for proving that SVT can enhance performance.
Anecdotal examples of the effectiveness of SVT are legion. For example, a professional boxer showed huge improvements in reaction times, eye-hand co-ordination, peripheral awareness and body balance after SVT. He became a world title contender and acknowledged that his success was largely due to SVT.
Another example involved a county cricket team. After pre-season SVT, the team improved on their previous year’s championship form to rise to the top of the league table, and a number of their players established themselves in the test team squad.
There have also been some good studies showing the benefits of SVT. Worrell divided 20 top-level baseball players into three groups, as follows:
1. An experimental group, given SV exercises designed to improve their performance;
2. A placebo group, given exercises with no specific effects on visual performance;
3. A control group who simply had their batting performance monitored.
Comparison of the groups showed that seven out of eight players in the experimental group improved their batting average during the season compared with three out of six in the control group and just one out of six in the placebo group(2).
Another researcher, Calder, trained only those faculties relevant to hockey and found her techniques endorsed in a double-blind controlled study (3).
The value of SV screening was demonstrated by Loran and Griffiths, who put all the under-14 players attached to a premier league football team through a series of SV tests. Those who were not retained for the following season because of deficits in their football skills were precisely the same ones identified by screening as the worst performers visually. This high correlation between SV ranking and ranking by coaches suggests that visual performance could be used as a guide to playing potential in younger players (4).
The visual system can, for simplicity, be divided into three parts:
1. Sensory (input)
2. Mental processing, or visual concentration
3. Motor (output).
All three must be highly in tune for good sporting performance; if not, there can be a knock-on effect whereby one failing leads to another. Only too often it is the middle section of the triad – visual concentration – that lets down performance. To work on this aspect of SV, equipment is ‘yoked together’ to add complexity, and therefore enhance concentration. For example, an athlete can use the saccadic fixator to train eye movements while simultaneously keeping a balance board still, being distracted by strobe lighting and answering questions!
Anatomically, there are two main neuro-visual systems, with separate functions, and parallel processing of both is needed for optimal sporting performance. The magno (large) cell pathway is concerned with peripheral vision, reaction time, co-ordination with other senses and concentration, while the parvo (small) cell pathway is concerned with clarity of vision, dynamic vision, spatial location and eye-tracking.
In sports like golf, cricket, skiing and sailing, where there is a genuine UV or ‘blue light’ hazard due to long days spent in sunlight, photo-protective eyewear is advisable. Without protection, the hazard can contribute to a variety of ocular conditions such as cataract, pterygium (overgrowth of the cornea) and macular degeneration.
Tinted filters and lenses work by increasing the contrast between target and background, thereby enhancing performance. In golf, a green tint with brown overtones increases the ball’s contrast against the blue sky and green fairway.
Clay pigeon shooters often use vermilion tints when aiming at orange clays against a moderately bright background, yellow tints in poor light and brown tints in very bright light. In tennis, a yellow tint, similar to the colour of the ball, highlights the contrast and visibility of the ball in overcast conditions (5).
SV research into binocularity has thrown up some interesting and surprising results. In one study, perception was found to be much more accurate in the left visual field than the right, irrespective of ocular ‘dominance’, and binocular vision emerged as vastly superior to monocular vision. Using both eyes, perception of stimuli in the left visual field was almost error-free. Eye dominance was not significant, and fewer errors occurred when the stimulus moved outwards rather than inwards. The implications of these findings for various sports, particularly with respect to stance, needs to be further examined(6).
Research with former Wimbledon tennis champions has shown that hitting the ball at a target was more accurate when the dominant rather than the non-dominant eye was blurred. This indicates that input to the binocular system is essential, and that the non-dominant eye plays a significant role in aiming (7).
Sometimes, and at certain distances, there may be no eye dominance. This can cause aiming problems as in the following example: a scratch golfer, when putting at about 12ft consistently hit the ball to the side of the hole. At shorter or longer distances there was no such problem. As he was a contact lens wearer, he was advised to wear only one lens when putting at 12ft during practice and report back on the outcome. This simple strategy resolved the problem and in future during play, he closed one eye when putting at about 12 ft since it was too impractical to remove his lens.
Research on decision making/information processing in badminton, using loops of film, revealed that experts make fewer errors than novices in predicting the trajectory of the shuttlecock. Experts predicted the shot four frames before the hitter made contact, whereas novices failed to predict the shot even two frames after contact. In other words, better players use only essential visual clues (8).
Similarly, using infra-red detectors, researchers discovered that successful footballers were the ones who knew where to look – ie those who made better and quicker use of eye fixations. To put it simply, experts extract better quality information by using better visual search strategies (9).
In conclusion, sports vision training is a relatively new discipline, but there is evidence that it works, and advice from an optometrist who specialises in SV can be a useful addition to all the other performance-improving techniques relied on by sportsmen and women. Athletes are advised to seek out a specialist SV practitioner via the Sports Vision Association (SVA) or RESCU on the internet.
Brian Ariel
