The author recognizes and acknowledges the influence of Drs. Bradley Coffey and Alan W. Reichow for much of the information contained in this chapter.
There is significant interest in improving sports performance by using training procedures to enhance vision because visual skills are readily identified as a critical element to most sports performance. Chapter 4 provides support for the contention that athletes typically have better visual abilities than nonathletes and that top athletes benefit from visual abilities that often are superior to lower level athletes. Sports vision training (SVT) has similar goals of transferring improvements in function to athletic performance as do other areas of performance training, such as strength training, conditioning, speed and agility training, nutritional regimens, and sports psychology. The relevant questions are whether visual abilities can indeed be trained and whether any improvements in visual skills transfer to improved sports performance by the athlete.
Many of the visual attributes identified as important in sports are amenable to training. This chapter presents SVT procedures for each of the visual skill areas, including any relevant laboratory and clinical research regarding skill improvement for these visual skills. Although few studies have attempted to demonstrate the transfer of visual skill improvement to actual sport performance, isolating one area of intervention as solely responsible for any changes in performance is quite difficult. Many of the reports in the literature are anecdotal, and many studies have significant flaws in the research design that preclude a definitive conclusion. Although there is a growing body of evidence supporting SVT approaches, the incomplete information regarding the efficacy of SVT clearly illuminates the need for more conclusive evidence.
Areas of Sports Vision Training
SVT procedures can be selected to accomplish the following potential goals of training:
Remediation of vision inefficiencies that may have a negative impact on performance consistency.
Enhancement of vision skills deemed important to optimal sports task performance.
Enhancement of visual information processing skills to facilitate rapid utilization of critical visual information.
Enhancement of visuomotor proficiency, when indicated, for sports task performance.
Enhancement of cognitive functions that are critical for visual decision-making during competition.
To determine the appropriate goals for an individual athlete, a thorough case history and sports vision evaluation must be completed. As discussed in Chapter 2, Chapter 4 , the sports vision practitioner must identify the vision factors essential to performance of the tasks critical for success in the sport and evaluate the quality of those skills in the most appropriate, accurate, and repeatable manner. A vision skill performance profile is recommended to communicate the relative strengths and “opportunities” demonstrated by the athlete from the sports vision evaluation, as described in Chapter 5 . The vision skill performance profile can be used to develop readily measurable specific goals for the SVT program to determine skill improvement. These goals should be consistent with the information processing model of skilled motor performance discussed in Chapter 3 , and each training procedure should be scrutinized to determine any impact on the three central cortical processing mechanisms: the perceptual mechanism, the decision mechanism, and the effector mechanism (see Fig. 3.1 ).
The athlete with identified visual deficiencies should logically expect improvement in affected aspects of sports performance if those deficient skills are improved to average performance levels. A review of the literature in 1988 concluded, “it is evident from the research presented that there is sufficient scientific support for the efficacy of vision therapy in modifying and improving oculomotor, accommodative, and binocular system disorders, as measured by standardized clinical and laboratory testing methods, in the majority of patients of all ages for whom it is properly undertaken and employed.” This conclusion was further supported by Ciuffreda in 2002. Therefore vision therapy designed to remediate vision deficits is an essential element in the comprehensive vision care of an athlete, and a successful result should improve the function of the perceptual mechanism.
The athlete who possesses average, or even above-average, vision skills presents a compelling and controversial challenge. Can the vision skills of this athlete be enhanced above the current level, and would this perceptual mechanism skill enhancement result in demonstrable improvements in sports task performance? A review of the literature concluded that most normal visual functions can be improved by specific training paradigms, although thousands of trials may be required to demonstrate enhancement. Several studies have reported positive effects of vision training programs on sport-specific tasks and some have not found improvement in performance. The differences in study results are speculated to be caused by varying athlete skill levels (novice vs. expert subjects), the use of general versus specific SVT programs, the lack of control or placebo training groups, and the lack of a sport-specific transfer test (referred to as perception-action coupling). Additionally, a variety of research design factors in many of these studies weakened the results and conclusions, indicating the need for further study in this area of sports vision.
Many SVT programs attempt to improve overall processing of visual information. Ultimately, the goal of the training procedures is to improve the speed and efficiency of the decision mechanism. This mechanism requires the athlete to know where crucial visual information exists, be able to direct attention to those crucial elements, select the best information from all that is available, organize and interpret the information in the most appropriate manner based on experience and memory of similar situations and information, and select the most accurate response with consideration of an anticipated action plan. Many studies have demonstrated that experienced athletes develop an organization of common sport situations into a knowledge architecture that offers many advantages, including the ability to process larger quantities of information in a short amount of time and the possibility of priming the perceptual and effector mechanisms for subsequent information. Recent advances in perceptual learning paradigms coupled with new digital technologies provide potentially useful platforms for SVT approaches that develop sport-specific visual-cognitive abilities.
Many sports require the translation of visual information into motor responses. For example, a tennis player must identify the anticipated trajectory of the opponent’s serve when the ball is struck and initiate the appropriate motor sequence to respond to that serve. SVT procedures that provide feedback regarding eye-hand, eye-foot, balance, and/or eye-body responses may assist the athlete in developing improved speed, efficiency, and automaticity of visuomotor response. This type of motor learning is thought to be the result of improved synaptic efficiency, and performance feedback is considered a critical element of enhancing performance of the perceptual and effector mechanisms. ,
The ability to modulate attention appropriately, and often split attention among multiple stimuli, is another valuable function of the decision mechanism in the information processing model. Many SVT procedures provide the opportunity for feedback to the athlete to facilitate development and control of visual attention. Additionally, as expertise is developed in a sport, the complex knowledge structures acquired facilitate expanded and enhanced use of mental imagery strategies. Mental rehearsal is the act of constructing mental images of an event, commonly used by elite athletes in preparation for performance. Studies have demonstrated that mental imagery may share the same types of neural processes as visual perception, which has significant implications in sports. Sport psychologists, and some sports vision practitioners, use methods designed to improve the mental imagery capacity and application by athletes, although only anecdotal evidence supports the validity of this approach.
Many goals are possible for an SVT program; some are hierarchic and necessitate a sequential strategy for use of specific procedures. The information processing model detailed in Chapter 3 can provide a framework for understanding the connection between the specific procedures and visual performance factors and ultimately sports performance.
Overview of Sports Vision Training
Once a visual performance profile has been completed and specific training goals have been established, specialized training procedures can be selected to accomplish those goals. Many idiosyncratic approaches to the selection of training procedures are available, from generalized programs administered to every athlete to precise, diagnosis-specific and task-specific individualized programs that are largely unique to the exact needs of each athlete. Each sports vision practitioner develops the approach that best suits his or her mode of practice; however, universal guidelines exist for SVT that should be heeded.
Training Hierarchy for Procedures
The development of an SVT program requires the practitioner to establish a series of procedures designed to improve, and progressively challenge, the visual skill(s) targeted for enhancement. The most important requirement of selecting training procedures is that the activity being performed must directly relate to specific task demands of the sport. The athlete will rarely invest the requisite effort needed for vision skill enhancement if the purpose of the procedure is not understood and correlated with sports performance.
Basic skill development procedures should be performed before challenging the athlete with more multifaceted demands. The visual skill targeted for enhancement should initially be isolated to allow the athlete to become aware of the visual response. With awareness of a visual response, strategies to improve the quality of the visual response should be discussed and practiced. An additional benefit of visual response awareness is the salutary effect on locus of attention; athletes can develop better control over modulation of attention during performance. Once a high quality of visual response is consistently demonstrated, the athlete should be pushed to increase the speed of the response while maintaining quality. Perceptual learning research has shown better training efficacy when participants understand the accuracy of their responses, use highly motivating tasks, and receive consistent reinforcement about the stimuli that are to be learned. The actual visual demands of the sport tasks should be considered when prescribing the training procedures; most visual demands encountered in sports occur well beyond arm’s length and in nonprimary gaze positions. Therefore many SVT procedures are designed to have viewing distances greater than 3 m, and the gaze position is adjusted to match the ecologic demands of the sport. For example, training activities for a volleyball player would be modified to have the targets presented at far and in upgaze positions to simulate the demands frequently encountered in volleyball.
The ultimate goal of the training program is to achieve an effortless, reflexive level of performance excellence in the targeted visual response ability—a level sometimes referred to as automaticity of response. The amount of attention that an individual must devote to accomplishing a task is a key variable in determining how automatic the response process is. A high level of automaticity allows the athlete to allocate attentional resources from visual performance factors to other important aspects of performance. Many methods are used in an effort to build automaticity of visual responses in a training program, most of which attempt to simulate the sport tasks ecologically and divert attention to additional tasks.
Many sports require the athlete to process visual information that is in motion and/or while the athlete is in motion. Training procedures that may initially be performed under static conditions therefore can be altered to add dynamic elements, such as incorporating movement of the target or athlete during performance. Automaticity of a visual skill response is often encouraged by modifying the training procedure from a paradigm of skill isolation to integration of additional visual skill demands. For example, the athlete attempts to maintain fixation on a swinging Marsden ball while balancing on a balance board and catching beanbags tossed from their peripheral visual field. Incorporating additional sensory demands is also common while performing a training procedure to more closely match the ecologic demands encountered in the sport situation and to build automaticity of the visual response. Common sensory integration demands include adding balance activities, auditory processing tasks, and increasing the levels of cognitive processing and distractions. These sensory integration demands serve to increase the stress experienced by the athlete and require the reallocation of attentional resources. Specific examples of all these automaticity variables are presented throughout this chapter.
The ultimate goal of SVT is to transfer visual skill improvements to the field of play. The practitioner should discuss strategies to facilitate skill transfer with the athlete. Recent perceptual learning research has demonstrated that learning is improved when individuals are presented with information from multiple sensory modalities, leading to better encoding and retrieval of perceptual information. Similarly, training on a diverse set of stimuli can assist in the transfer of learning to untrained conditions. Many of the approaches discussed for increasing automaticity of visual performance skills also provide a means of assisting transfer. For example, when an athlete can perform a visual task at a superior level despite many sensory integration demands, distractions, and stress loaded onto the activity, the more likely the athlete’s visual system will continue to perform at an optimal level during high-stress moments of competition and despite significant physical fatigue. Furthermore, some “naturalistic” SVT procedures have the athlete practice actual or simulated sporting activities with the addition of specific training elements that alter or augment the visual demands. Athletes, athletic trainers, coaches, and other ancillary personnel can be invaluable resources for assisting in the development of on-field modifications to training procedures, thereby providing additional support for the transfer of skill improvements.
Taxonomy of Sports Vision Training
This overview of SVT, as well as many of the published studies utilizing SVT, represents a predominantly component skill training approach. Component skill training is based on the construct of skilled motor performance as the outcome of many visual subprocesses. This type of SVT is designed to eliminate obstacles in the visual information processing pathway in order to optimize performance. In a review article, four types of component skill training approaches were identified: “ Low-Level Visual Instruments that target foundational visual skills, Perceptual-Cognitive Training Instruments that target generalizable visual-cognitive abilities, Visual-Motor Reaction Training that targets neuromuscular function, and Integrated Sensorimotor Batteries that bridge all these domains.” Studies have demonstrated improvements in fundamental visual abilities when applying perceptual learning approaches to component skill training, showing that practice can produce substantial improvements that can last for months or years. More importantly for SVT, perceptual learning benefits have been shown to transfer to new untrained contexts. ,
As mentioned previously, some SVT approaches have the athlete practice actual or simulated sporting activities with the addition of specific training elements that alter or augment the visual demands. These approaches have been called naturalistic SVT approaches in contrast to component skill training because they do not reduce the training context to the foundational elements of visual information processing. Naturalistic SVT procedures provide the athlete with a natural performance environment while facilitating manipulations that can accelerate skill development. In a review article, three types of naturalistic training approaches were highlighted: “ Stroboscopic Visual Training that uses eyewear to interrupt normal visual input, Eye Tracking interventions that train gaze behavior, and Simulations that recreate the sporting environment in virtual reality contexts.” The perceptual learning literature suggests that transfer of a training effect is facilitated by the training and transfer tasks involving overlapping cognitive processes. These principles of naturalistic training highlight perception-action coupling encompassing a high level of similarity between training and real-life performance. Many SVT programs provide elements of both component skills training and naturalistic training approaches to maximize the benefits of the program.
An SVT program provides the athlete with the conditions and opportunity for the improvement of critical visual skills; the equipment or activities themself do not cause the changes in performance. A baseball player can spend many hours in batting practice to develop the requisite skills for success, but if proper coaching is not available the athlete may simply reinforce inefficient or ineffective skills. Similarly, an innovative new bicycle does not allow an athlete to win the Tour de France; the effective use of that bicycle, unflagging motivation, and many other intangibles culminate in success. Therefore athletes should be thoroughly counseled regarding the commitment required for a successful outcome from an SVT program. A typical program will require frequent training sessions and many hours of quality practice to enhance visual performance successfully, and the athlete needs to fully understand the nature of this commitment. If the practitioner is not convinced that the athlete possesses the essential resources of motivation, time, and support for success with an SVT program, the athlete should seek other approaches for enhancing sports performance.
Similar to most physical and psychologic enhancement programs, the more quality effort the athlete invests in the program, the greater the potential impact on sports performance. The athlete must have the motivation to devote sufficient time and energy into developing the targeted visual skills to achieve a successful outcome. A dedicated support network (e.g., coaches, parents, teammates, family, friends) is an invaluable asset for sustaining the motivation of an athlete throughout the course of the SVT program. Members of the support network can also serve as training partners for the athlete when practicing visual performance activities between training sessions. One of the best methods of generating motivation is excellent education regarding the connection between visual skill performance and sports performance. For example, the better the golfer understands how reduced depth judgment ability affects putting performance, the better the motivation will be to improve that visual skill. This also applies to the athlete’s support network because coaches, trainers, and teammates can provide valuable performance feedback and reinforcement of proper skills during practice and competition.
Specific training goals should be established before initiating an SVT program and measurable outcomes are desirable in determining program success. Training goals must be as task specific as possible. For example, rather than the point guard in basketball setting a goal of being a better playmaker, the point guard can establish a goal of improving his or her ability to process more peripheral visual information when bringing the ball up the court. These specific sports goals should be matched with goals of improving the requisite, and measurable, visual performance skills necessary for success. Once the specific goals have been determined, more global competitive aspirations can be recognized to assist in motivating the athlete. For example, the basketball player may wish to be the starting point guard on the team, garner a college scholarship, or be drafted by a professional team. No matter what level of competition the athlete is in, visual performance goals can be established to provide a potentially critical competitive edge for peak performance.
Delivery of Sports Vision Training
Many approaches can be used for the delivery of SVT. Most practitioners use one-on-one training sessions to assess the athletes’ current visual skill performance and push the demand level of those skills to a higher level. These sessions are typically conducted by the eye care practitioner or a trained assistant. Others develop training programs to be delivered to a team or group of athletes simultaneously, although this approach reduces the ability to adjust the training program to each athlete’s individual visual performance needs. Once the threshold of performance ability is determined during a training session, activities are customarily prescribed to allow the athlete to practice at that high demand level until the next session. A regular schedule of progress evaluations should be established to periodically assess both subjective changes in sports performance and changes in objective visual performance skills. These progress evaluations serve to reinforce training goals, maintain athlete motivation, and determine when specific goals have been achieved.
When an SVT program is recommended to an athlete, an estimated treatment period should be determined. The practitioner and the athlete can then agree on the appropriate frequency of one-on-one training sessions, the length of time for each session, and the location for the sessions. Depending on the intensity of the training program and the availability of the athlete, training sessions may occur two to three times per week or every 2–3 weeks. Each training session usually lasts at least 30 min and may be scheduled for up to 90 min if needed. The practitioner typically delivers the training program at his or her office, where equipment and supplies are located; however, receiving the training at the athlete’s sports training facility may be more convenient for the athlete. A candid discussion of the advantages and disadvantages of the available location options should occur and an agreeable solution reached before initiating the training program. Prescribed out-of-office training activities typically require an average of 30 min each day of dedicated practice and should be integrated with any existing training programs (e.g., weight training, speed training, skills practice) if possible. The incorporation of visual skills training with other training programs can help with compliance and transfer of skill improvements to sports performance. This is also an efficient approach because there are often periods of recovery during a program of strength and conditioning activities and the athlete can work on SVT procedures during these recovery periods. The athlete should understand that the quality and frequency of out-of-office practice produce the greatest impact on skill development, and the athlete should not assume that the one-on-one training sessions alone will improve performance.
Expectations of Sports Vision Training
As previously mentioned, specific training goals should be established before initiating an SVT program and training goals should be as task specific as possible. If these goals are reasonable and the potential outcomes of the training program are clear, the athlete is more likely to have a realistic expectation of the benefits of committing to the training program. If the athlete has unrealistically high expectations or the practitioner makes unrealistic promises, disappointing results are inevitable. The practitioner and athlete should acknowledge that the training program is designed to improve only one aspect of sports performance. Even though vision may be a critical factor for successful sports performance, many other aspects may hinder performance. If the practitioner makes unrealistic promises and is not successful in achieving those goals, the program will not be perceived as successful by the athlete and his or her support network. If the athlete perceives that SVT is unsuccessful, that perception will be difficult for the practitioner to overcome when it is communicated to others in the sporting community. The old adage that it is better to underpromise and overdeliver is particularly relevant when setting goals and promising outcomes from SVT programs.
Vision Skill Remediation and Enhancement
Over the years, many practitioners have contributed suggestions and ideas for visual performance enhancement procedures to the collective community of sports vision practitioners. The origins of each procedure or modifications of a procedure are often hard to identify, making proper credit difficult. The following suggested procedures have been culled from publications, lectures, and professional interactions, which makes identification of individual sources even more difficult. Although the following procedures do not represent all training procedures that have been developed, they have all been found to be effective by the author in clinical practice.
Visual sensitivity: acuity and contrast sensitivity
The primary goal of training is to improve the athlete’s ability to discriminate subtle details in the sport environment. Many examples in sports exist in which an athlete must judge finely detailed information to determine the most appropriate response. For example, the more sensitive a golfer is to the subtle contours of the green, the better his or her judgment will be of the optimal putt trajectory. This example of putting includes resolution of the details of the green as well as any muted contrast changes induced by the surface contours and variations in the grass. Several procedures encourage interpretation of blurred images, which may also help extract detailed information from a rapidly moving object.
Ample evidence shows that the ability to resolve detail can be enhanced with practice, both for foveal detail and parafoveal information. Most of the studies have involved blur interpretation in subjects with myopia; however, most studies did not find a change in refractive status from the training. , , Contrast sensitivity function has also been shown to be amenable to enhancement with practice, as has vernier acuity. , ,
This procedure introduces lenses of varying powers that the athlete must classify while viewing a distant target. This procedure is performed monocularly to eliminate the interaction with the vergence system, and the choice of fixation targets should relate to the task demands of the sport. For example, having a golfer fixate a golf ball positioned 3–6 m away rather than a chart of letters is preferable to simulate the visual task demands of golf. The athlete is asked to distinguish how the lens affected his or her view of the target. The athlete is encouraged to notice induced changes in size, location, and clarity of the target. Improved sensitivity to lens-induced changes of spatial information is theorized to have a salutary impact on depth discrimination because these monocular cues to depth are abundant in many sports tasks (e.g., catching a fly ball in baseball). An athlete may also notice a difference in the amount of effort required to achieve clarity with minus lenses, and this additional information should provide enough cues to discriminate a 0.25 D difference in lens powers. To promote improved sensitivity to retinal image size without the feedback from the accommodative system, iseikonic lenses can be substituted. Iseikonic lenses allow comparison of small changes in image size without changing the focusing demand for the target. Ultimately, sensitivity to 0.12 D and 0.5% magnification or minification changes should be the goal for sports requiring detail discrimination or precise depth judgments. Targets can also be presented in the athlete’s periphery to stimulate improved sensitivity to peripheral discrimination, which may be valuable in sports such as downhill skiing.
As discussed in Chapter 3 , the perception of motion in depth is partially produced by a changing retinal image size information system that operates relatively independent of the changing retinal disparity system. Human beings possess cortical neurons that are selectively sensitive to changing image size, and these “looming” detectors provide a significant amount of information for judging time to contact even under monocular viewing conditions. Binocular viewing has been shown to offer advantages in catching or hitting a ball ; however, monocular catching ability can be trained to similar skill levels as binocular viewing. For sports that require an athlete to make rapid depth judgments of approaching objects (e.g., a tennis ball), sensitivity to subtle changes in image size may provide a valuable advantage.
A Howard-Dolman apparatus can be used to enhance sensitivity to monocular cues to depth. A traditional Howard-Dolman device is a modification of the apparatus designed to measure the empirical longitudinal horopter and uses two rods of equal size and color to be viewed in primary gaze position through an aperture in a rectangular box of a homogeneous color (see Fig. 4.4 ). The athlete makes depth judgments concerning the apparent location of the two rods under monocular viewing conditions instead of the traditional binocular method. This procedure can be further modified for sports purposes by substituting two identical balls or objects, such as golf balls, tennis balls, or shooting clays. The initial goal of training is to refine the athlete’s sensitivity to subtle monocular cues to depth. The athlete is then obligated to make the depth judgments in progressively shorter periods (tachistoscopic presentation).
Low amounts of prism are used to increase visual sensitivity to target movement in a similar manner as lens sensitivity. A prism is introduced monocularly, with a random orientation of the prism base, while the athlete views a fixation target such as a golf ball, soccer ball, or shooting target. The initial goal for the athlete is to detect the direction of the target movement induced by the prism. As the athlete becomes more accurate in identifying spatial shifts stimulated with very small amounts of prism (e.g., 0.5–1 Δ ), the athlete is encouraged to make those fine judgments in progressively shorter time intervals.
Haidinger brush fixation
In sports that require steadiness of fixation, such as target shooting, the visual biofeedback provided by the entoptic phenomenon of a Haidinger brush can be valuable. The perception of the Haidinger brush is generated by variable absorption of plane-polarized light by Henle fiber layer of the macular retina. The athlete learns to maintain accurate and steady fixation of the Haidinger brush and achieves a proper state of concentration, reducing the tendency for fixation to drift off target. Di Russo et al. demonstrated that elite shooters possess better fixational ability than novice shooters and can maintain the accuracy of fixation despite the presence of distractions. The Bernell Macula Integrity Tester 2 ( www.bernell.com ) is a commercially available device that produces the entopic phenomenon; many slides are available that contain various fixation targets ( Fig. 8.1 ). The athlete should become aware of the feeling required for the proper concentration needed to maintain accurate and steady fixation in order to reproduce that level of concentration during sport practice and competition. As the accuracy and steadiness of fixation improve, distractions should be introduced during Haidinger brush training to simulate competition conditions and build automaticity of concentration and fixation.
Blur interpretation activities
Many studies have successfully demonstrated the ability to improve the threshold visual acuity level in subjects after a course of training. , The procedures used to improve acuity generally involve the reduction of target size or clarity to a level that is barely subthreshold for the subject and then guessing is encouraged as the targets are changed. Ample feedback is provided with each guess until the accuracy of target discrimination improves to a satisfactory level, at which time the target size or clarity is further reduced to a subthreshold level. When using this paradigm with athletes, the ability to discriminate subtle details from blurred or minuscule targets is enhanced. In sports that require rapid discrimination, such as batting in baseball, tachistoscopic presentation of stimuli is introduced as each level of performance is mastered.
Many targets and methods for reducing image clarity can be used to enhance the sensitivity of visual discrimination ( Box 8.1 ). Random sequences of letters and numbers can be printed from a computer by using progressively smaller font sizes, and those targets can be held at increasing distances from the athlete as he or she attempts to discriminate the targets. The targets can be further degraded by having the subject view through filters that decrease the amount of visible light transmission or by reducing the light levels on the targets, thereby increasing the demand on contrast sensitivity to discriminate the targets. The athlete can also wear lenses that induce blur, such as lenses that overplus the athlete or lenses with degraded optics (e.g., stippled lenses). Bangerter foils can also be used to provide a graded reduction in acuity through the lenses ( Fig. 8.2 ). These same acuity-degrading lenses can be worn during practice sessions of the athlete’s sport (e.g., during putting practice in golf), and the athlete can experience the perceived enhancement of visual discrimination when the lenses are removed. The steps for this type of SVT procedure are (1) practice the activity without the foil goggles for a short period (e.g., 2–5 min); (2) repeat the activity with the foil goggles for 5–10 min, work to increasing foil density (change foils after three to five successes at a level); and (3) remove the foil goggles and repeat activity for at least 5 min to maximize retention of improved performance. The safety of the athlete must be preserved during this activity, especially when a risk to the athlete is present, such as during batting practice in baseball. The use of sports protective eyewear for the training is recommended when there is any perceived risk to the athlete. As described with the other visual sensitivity training activities, tachistoscopic presentation of stimuli is another important step for enhancing the speed of visual discrimination.
Threshold acuity targets or increasing distance
Degraded optics (e.g., stippled lenses)
Lenses with excessive plus power
Lenses with excessive minus power (minification)
Reduced light levels
Ultimeyes ( www.ultimeyesvision.com ) is a custom video application incorporating diverse stimuli, adaptive near-threshold training with learning-optimized flickering stimuli, and multisensory feedback in a digital training program designed to improve foundational aspects of visual sensitivity by applying the tenets of perceptual learning. In a series of studies, the Ultimeyes app has demonstrated improvements in visual acuity and contrast sensitivity in both nonathletes and athletes, as well as improved batting performance in collegiate baseball players. , There are other computer-based applications that are available to train visual acuity and contrast sensitivity, but these are not constructed for sport-specific purposes.
As previously discussed, incorporating additional sensory demands while performing these visual sensitivity training procedures is essential to more closely match the ecologic demands encountered in the sport situation and to build automaticity of the visual response. Many of these procedures allow the practitioner to include the addition of balance activities, auditory processing tasks, and increased levels of cognitive processing and distractions in order to increase the stress experienced by the athlete ( Box 8.2 ). Cognitive demands can be included in two principle approaches: questions that the athlete must attempt to answer while performing the task or verbal distractions that the athlete must ignore. The choice of cognitive demands is based on the task demands of the sport. Balance activities typically entail the use of balance boards ( Fig. 8.3 ) or walking rails ( Fig. 8.4 ). The training effect from these types of procedures has been shown to transfer to stimuli not used during training , and to improvements in contrast sensitivity function. Evidence also exists that the training effect is produced at a level beyond the retina because the training effect has been shown to transfer to an untrained eye. , Training with sport-specific stimuli, such as baseball pitches, has also been shown to improve dynamic visual acuity and batting ability.
Auditory “noise” stress
Cognitive challenges (questions)
Peripheral vision processing (e.g., beanbags)
Dynamic visual acuity
Many sports require the athlete to discriminate visual information that is moving, such as judging the speed and trajectory of a tennis serve. Traditional static visual acuity training may not fully address the visual demands encountered in some types of sports. Athlete attributes that can affect dynamic visual acuity (DVA) include the resolving power of the retina (visual sensitivity), peripheral awareness, oculomotor abilities (pursuit and saccadic eye movements), and psychologic functions that affect interpretation of visual information. DVA has been shown to be improvable with training, , with the training effect being most evident for the most challenging stimuli and tasks used in the studies. Enhancement training for DVA is frequently recommended for athletes. , , , However, the nature of the training varies tremendously and few instruments are available to generate the necessary targets. Some practitioners recommend using targets that move toward the athlete and some advocate for rotational targets. , Incorporation of a tachistoscopic presentation of the moving stimuli is valuable in sports for which the athlete must quickly fixate critical visual information and discriminate vital details, as in judging the trail contours when mountain biking. A study with collegiate softball players found that a program of SVT improved performance on the Target Capture (DVA) assessment of the Senaptec Sensory Station.
Rotators with disks and charts
Target size is selected at a level that is at threshold for the athlete, and the target is placed on a rotating disk (see Fig. 4.1 ) and rotated at a speed that is too fast for the athlete to discriminate the target. Many targets can be used to enhance the sensitivity of visual discrimination while the targets are in motion. The athlete is encouraged to guess what the target is as the speed is slowly reduced to the point where accurate discrimination is achieved. Ample feedback is provided with each guess until the accuracy of target discrimination improves to a satisfactory level, at which time the target size is further reduced to a new threshold level or the athlete is moved further from the target. When using this modified paradigm of method of limits, the ability to discriminate subtle details from rapidly moving targets is enhanced. This approach is meaningful for sports in which the movement of the target is mainly predictable (e.g., a baseball pitch); however, it may have a limited benefit in unpredictable sports (e.g., downhill skiing). Additional visual discrimination demands and sensory integration burdens can be added to this task, as previously described with blur interpretation activities.
Wayne tachistoscope rotator activities
The Wayne Tachistoscope Rotator Scanner was composed of two prisms that could be rotated in front of a Perceptamatic tachistoscope lens ( Fig. 8.5 ). The speed at which each prism rotated could be adjusted between 20 and 240 rpm, allowing a projected image to move in a variety of directions. A variety of slide reels were available with images of numbers, arrows, patterns, and sports images (e.g., football, baseball pitches). These images could be presented for durations between 1 and 0.01 s, facilitating the training of short-exposure dynamic visual acuity. The product is no longer available and there is currently no similar product available. It is possible to program a computer-based application to replicate the vision demands created by this instrument and repeatability could be improved with a digital version. The use of ecologically appropriate targets or real-time videos would be preferred in order to produce a better simulation of the DVA demands encountered in a sport; however, gathering a suitable library of sport-specific images or videos from the athletes’ perspective would require considerable resources.
Pitchback or ball machine with ball and letters
A rubber or soft baseball with letter stickers placed randomly around the ball is commonly used for the pitchback procedure ( Fig. 8.6 ). The athlete throws the ball into a pitchback net and attempts to locate and fixate one of the letters on the ball during the return flight. As the athlete’s ability to discriminate the letters improves, the ball is thrown faster into the net; more spin can be induced by the athlete during the throw. To add a level of unpredictability to the task, the ball can be thrown by another person, thereby requiring the athlete to rapidly judge the speed and trajectory of the ball during flight. Once the athlete can demonstrate consistently accurate ability in this task, additional visual discrimination demands and sensory integration burdens can be added. If a pitchback is not available, the athlete can have someone throw the ball back, bounce the ball against a wall, or throw the ball high in the air to simulate the sport demands.
A variation in this procedure is the use of a ball machine rather than a pitchback. The distance and speed of the ball machine can be set for the preferred demand level. The machine is loaded with balls containing images to be discerned by the athlete, such as colors, shapes, numbers, or letters. The athlete is instructed to respond to a specific target (e.g., balls with a green dot or letter) and inhibit response to other targets (e.g., balls with a red dot or numbers). This modification can be done with tennis and baseball, softball, or cricket batting.
Accommodation and vergence facility
Accommodative and vergence facility training procedures aspire to improve the ability to rapidly adjust focus and eye alignment for the variety of fixation distances encountered in sports. Two principal methods are used to change accommodative and vergence demands: the use of lenses or prisms to alter the accommodative and vergence demands at a fixed distance and the use of charts or targets at different distances, with fixation being rapidly alternated between the targets. When lenses are introduced, the accommodative system must adjust ciliary muscle tonus to regain image clarity; however, the vergence system must remain aligned with the plane of the target to prevent diplopia. This separation of accommodation and vergence is a common method to improve relative accommodative facility binocularly at near in patients with asthenopia during near work. However, it is not generally representative of the visual task demands experienced in sports. Charts or targets placed at different distances allow the accommodative and vergence responses to remain paired. Therefore procedures that use targets at a variety of different distances may be more appropriate for enhancing the strength and flexibility of focusing and eye alignment in athletes. A study with collegiate softball players found that a program of SVT that included distance rock activities improved performance on the Near-Far Quickness assessment of the Senaptec Sensory Station. If a student athlete has symptoms of asthenopia during near work, the more traditional use of lenses and prisms may be warranted to alleviate those symptoms. A study of female ball sports athletes at a university found that some aspects of vergence function were effectively improved by an SVT program and that the effects were retained after 4 weeks.
Charts with random letters ( Fig. 8.7 ) are placed at a relatively far distance from the athlete, usually more than 10 feet, and at a near distance, usually within 50 cm. The athlete stands as far away from the distant chart as possible while still being able to read the letters. The athlete should start by holding the near chart at arm’s length and slowly move it closer until the letters are too blurred to recognize. The athlete should take 2–3 s to try to clear the letters before adjusting the chart to a slightly further distance, where the letters can again be cleared. The task requires the athlete to then clear and call out successive letters on each chart alternately as rapidly as possible, making sure to achieve maximal visual clarity with each fixation. This procedure initially can be performed monocularly to equalize accommodative facility in each eye individually, and the choice of viewing distance and positions of gaze should be based on the task demands of the sport. Once the athlete can demonstrate consistently accurate precision and speed on this task, additional visual discrimination demands and sensory integration burdens can be added.
A chart with random letters or words (e.g., reduced Hart chart, accommodative rock cards) is placed at a near distance, usually 40 cm. Lenses of various powers are placed in front of the athlete’s eyes and the athlete is instructed to make the letters or words clear again as rapidly as possible. The athlete should be able to feel the difference between when accommodation is stimulated and when accommodation is released. Monocular lens sorting is a useful procedure for developing awareness of accommodative effort. Lens sorting requires the athlete to organize a variety of loose lenses into a sequence based on power. For example, a series of minus lenses is provided, ranging from −0.50 D to −4.00 D in 0.50-D steps. The athlete is instructed to clear a designated target through each lens; based on the apparent changes in image size and the accompanying feeling of accommodative effort, the athlete arranges the lenses from the weakest to the strongest power. A typical goal is sensitivity to differences of 0.25 D.
Lens rock procedures are usually performed monocularly at first, and binocular lens rock procedures are introduced once an acceptable level of performance is achieved monocularly. Lens flippers of various powers are used for binocular training; one side of the flippers contains minus lenses and the other side has plus lenses. Once the athlete can demonstrate consistently accurate precision and speed on this procedure, additional visual discrimination demands and sensory integration burdens can be added.
The goal of lens rock training is to increase the speed and accuracy of the accommodative response induced by the lenses. Although remedial vision therapy for accommodative dysfunctions emphasizes development of the ability to clear relatively large lens powers rapidly (e.g., +2.50/−2.50 D), this may not offer a significant advantage for an athlete during sports performance. As previously mentioned with lens sensitivity procedures, sensitivity to subtle changes in image size may provide a valuable advantage through enhanced sensitivity to monocular cues to depth. Therefore awareness of image size changes with brisk accommodative changes may yield supplementary performance benefits above the traditional goal of extending the range of accommodation.
Prism sensitivity should be performed before initiating training with prism rock procedures to ensure that the athlete can accurately identify spatial shifts stimulated with very small amounts of prism (e.g., 0.5–1 Δ ). Prism flippers of various powers are used for vergence facility training; one side of the flippers contains base-out prisms and the other side has base-in prisms. A threshold acuity target is placed at an appropriate distance based on the task demands of the sport. One side of the prism flippers is placed in front of the athlete’s eyes and the athlete is instructed to make the target single and clear again as rapidly as possible. The athlete should be able to feel the difference between a positive and negative fusional vergence demand. Once the athlete can demonstrate consistently accurate precision and speed on this procedure, additional visual discrimination demands and sensory integration burdens can be added.
The goal of prism rock training is to increase the speed and accuracy of the vergence response induced by the prisms. Although remedial vision therapy for vergence anomalies emphasizes development of ability to rapidly fuse relatively large prism powers (e.g., 10 Δ base out/10 Δ base in), this may not offer a significant advantage for an athlete during sports performance. Similar to lens rock procedures, awareness of image size changes and apparent spatial localization shifts induced by brisk vergence changes may yield supplementary performance benefits beyond the traditional goal of extending the range of fusional vergence. The athlete is encouraged to localize the perceived location of the target through each prism power to provide feedback regarding spatial judgments.
The ability to maintain fixation of a rapidly moving object is frequently a critical aspect for allowing visual processing of crucial information in sports. The ability to change fixation from one location to another rapidly and accurately is also an essential aspect of many sports tasks. In nondynamic sports such as precision target shooting, the ability to maintain steady fixation is a vital aspect of successful performance. Many training procedures have been developed to provide feedback regarding performance accuracy and speed of eye movements. Most of these procedures applied to athletes are modified therapy procedures originally designed to improve deficient eye movements in children, and the primary goal for these procedures is to improve eye movement efficiency for reading-type tasks. The Haidinger brush fixation activity previously described can be used to enhance control of fixation steadiness by providing direct visual feedback. A task analysis of the specific eye movement demands involved in an athlete’s sport gives the practitioner essential insight that can be used to modify therapy procedures to target specific sport-related eye movement skill development.
Poor eye movement control is difficult to find in a successful athlete; this deficiency is more commonly found in the emerging youth athlete who is attempting to acquire performance skills. These young athletes are more apt to yield significant benefits from training procedures directed at improving eye movement efficiency. For the more seasoned athlete, the goal is often enhancement of performance capacity during high-stress situations in which accurate and rapid eye movement control is a critical factor. Ultimately the goal of enhancement training is to improve automaticity of eye movement performance so that minimal attention is required for skilled performance. The work of Hebb and others supports the concept that development of visual performance skills should be elevated to a level that requires minimal attention so that attention can be selectively distributed to other crucial aspects of performance. Eye movement training must involve additional sensory integration burdens and cognitive processing demands to elevate the athlete’s automaticity of accurate eye movement control and ability to modulate attention during performance.
Pursuit eye movements
The Marsden ball is commonly used to provide feedback regarding pursuit eye movement accuracy. The Marsden ball is a soft baseball with random letters placed around the sphere that is suspended from the ceiling with a string that allows it to swing in various trajectories ( Fig. 8.8 ). The athlete is challenged to maintain fixation on specific letters on the ball while it is swung in various patterns. The exercise typically begins with the ball swinging on a plane perpendicular to the athlete’s line of sight so the relative depth of the ball does not change while it is swinging. The athlete is encouraged to maintain a steady head position with instructions to only follow the ball with his or her eyes. When performance becomes smooth and efficient, the ball is swung in elliptical trajectories that induce changes in relative depth throughout the course the ball travels.
The athlete should be given verbal feedback regarding the accuracy of smooth pursuit eye movement performance during this activity so that he or she becomes aware when pursuit eye movements break down into saccades. A visual afterimage can be used to improve the feedback for the athlete when he or she has difficulty elevating the awareness of pursuit eye movement accuracy. An afterimage can be generated with a masked camera flash or similar commercially available device ( Fig. 8.9 ). The athlete is asked to fixate a central spot monocularly on the flash unit held with the light portion oriented vertically approximately 25 cm from the eyes and the light is flashed. The athlete should then see a vertical streak of light wherever fixation is directed so that fixation accuracy can be monitored while pursuing the Marsden ball. If the athlete is having difficulty seeing the afterimage, rapid blinking and dimming the room lights should enhance the appearance of the image.
Once the athlete has achieved accurate pursuit eye movement performance with the Marsden ball, sensory integration activities are incorporated. A motor response is commonly added to the task by asking the athlete to locate and point at letters on the ball as an index finger pokes the letter on the ball hard enough to make it swing in an arc away from the athlete. Each time the ball swings back toward the athlete, he or she is instructed to locate and track a different letter until he or she can alternately poke it with the right or left index finger. Another motor element that can be added to the Marsden ball procedure is to have the athlete hold a stringless racquet (tennis, squash, racquetball) under the ball while it is swinging. The athlete is further instructed to raise the racquet on command and encircle, or hoop, the swinging ball without touching either the ball or the string.
Because many sports require the athlete to track a moving object or person while maintaining balance, adding a balance demand to the Marsden ball activity is particularly beneficial. The athlete is instructed to stand on a balance board and achieve steady balance while fixating a motionless Marsden ball. Once the athlete has attained steady balance, the ball is swung while the athlete attempts to maintain balance and fixation with smooth pursuit eye movements. Pursuit eye movements will induce vestibular responses that the athlete must override to maintain steady balance. The athlete can be further challenged with the elliptical trajectories and motor response activities previously described. Additionally, if the athlete competes in a sport that requires awareness of peripheral information while processing central visual information, the trainer can randomly toss beanbags at the athlete from a peripheral location that the athlete must either catch or block during performance. This is also an excellent activity to add cognitive challenges to the task demand. The athlete can be instructed to either answer questions that are asked at random intervals during performance or ignore the distracting chatter in the background.
Saccadic eye movements
Charts with random letters (see Fig. 8.7 ) are placed at a relatively far distance from the athlete, usually 10 feet or more. The task requires the athlete to find and call out successive letters on the chart as rapidly as possible, making sure to achieve visual clarity with each fixation. The athlete is instructed to call out the first letter and last letter of each row (O, E, Y, X, etc.) until the bottom of the chart is reached. With successful execution of this task, the athlete is instructed to call out the second letter and the next-to-last letter of each row, the third letter and the third-from-last letter of each row, or other challenging saccade patterns. Multiple charts can also be used, with fixations moving either in a predetermined sequence between charts or at the command of the trainer. Accuracy of saccadic performance can be monitored through observation by the trainer and verbal feedback provided to the athlete regarding any overshooting or undershooting of saccadic eye movements. Further visual feedback can be provided with a visual afterimage, as previously described. The goal is smooth, quick performance with each pattern of saccadic eye movements.
Once the athlete can demonstrate consistently accurate precision and speed on this task, additional visual discrimination demands and sensory integration burdens can be added. The use of a metronome is a particularly effective method for enhancing auditory-visual integration, and increasing the pace of the metronome can generate performance stress similar to athletic competition. When adding a metronome to this procedure, the athlete is challenged to correctly call out a letter on each successive chart with the beat from the metronome. Polarizing filters also can be worn to increase the contrast demand of the task, or lenses with degraded optics can be used to simultaneously enhance blur interpretation. Because many sports require the athlete to make rapid saccadic eye movements while maintaining balance, adding a balance demand to this activity is particularly beneficial. The athlete is instructed to stand on a balance board and maintain steady balance while performing the saccadic task. Additionally, if the athlete competes in a sport that requires awareness of peripheral information while processing central visual information, the trainer can randomly toss beanbags at the athlete from a peripheral location that the athlete must either catch or block during performance.
A chart with arrows pointing in random directions can be substituted for a letter chart ( Fig. 8.10 ). The arrow chart provides a method for adding a motor performance feature to the saccadic eye movement tasks. For example, the athlete can be instructed to move his or her feet in the direction of the arrow being named (right, forward, etc.) or move a balance board in the direction indicated by each arrow. This sensory integration activity can also be performed with the athlete’s hands or while holding a racquet, bat, or hockey stick, for example. Computer programs also are available for saccadic eye movement training with an arrow stimulus in a random orientation presented in a random location of the computer monitor that the athlete must respond to as quickly as possible by moving a joystick (or arrow key) in the same direction as the arrow. This is also an excellent activity to add cognitive challenges to the task demand. The athlete can be instructed to either answer questions that are asked at random intervals during performance or ignore the distracting chatter in the background.