Ординатура / Офтальмология / Английские материалы / Sports Vision Vision Care for the Enhancement of Sports Performance_Erickson_2007

these types of procedures has been shown to transfer to stimuli not used during training37-39,43 and to improvements in contrast sensitivity function.40-42 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.37,44

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 include the resolving power of the retina (visual sensitivity), peripheral awareness, oculomotor abilities (pursuit and saccadic eye movements), and psychological functions that affect interpretation of visual information.71-95 Dynamic visual acuity has been shown to be improvable with training,96,97 with the training effect being most evident for the most challenging stimuli and tasks used in the studies.97 Enhancement training for dynamic visual acuity frequently is recommended for athletes.1,5,98-104 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,98 and some advocate for rotational targets.1,98 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.

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. 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 in 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 (www.wayneengineering.com) is composed of two prisms that can be rotated in front of a Perceptamatic tachistoscope lens (Fig. 8-5). The speed at which each prism rotates can be adjusted between 20 and 240 rpm, allowing a projected image to move in a variety of directions. A variety of slide reels are available with images of numbers, arrows, patterns, and sports images (e.g., football, baseball pitches). These images can be presented for durations between 1 second and 0.01 second, facilitating the training of short-exposure dynamic visual acuity.

Figure 8-5. The Wayne Tachistoscope Rotator Scanner.

The athlete is placed at a distance from the images that approximates a threshold visual acuity demand and is then shown the area where the projected image will appear. With an auditory cue, the image is presented for a predetermined exposure time while the image is moving in a direction determined by the rotation of the prisms. The athlete must locate and fixate the moving image and maintain fixation with a pursuit eye movement during the exposure of the image to resolve the detail in the slide. Additional visual discrimination demands and sensory integration burdens can be added to this task, as previously described with blur interpretation activities. Furthermore, asking the athlete to respond to the target stimuli with an appropriate motor response is often beneficial. For example, with a slide of a tennis serve, the athlete is instructed to move into a backhand or forehand return position in response to the anticipated trajectory of the serve.

The use of ergonomically appropriate targets is preferred; however, few sport-specific images are available. Real-time video images presented tachistoscopically would produce a better simulation of the dynamic visual acuity demands encountered in a sport; however, considerable resources are required to develop a library of appropriate footage from the athlete’s visual perspective.

Pitchback with Ball and Letters

A rubber baseball with letter stickers placed randomly around the ball is 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

Figure 8-6. A rubber baseball with letter stickers in front of a pitchback.

accurate ability on this task, additional visual discrimination demands and sensory integration burdens can be added. If a pitchback is not available, the athlete can either 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.

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; 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 train relative accommodative facility binocularly at near in patients with asthenopia during near work.105-107 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. 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.

Distance Rock

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

Figure 8-7. Hart’s revised vision chart.

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 with reduced images at arm’s length and slowly move it closer until the letters are too blurred to recognize. The athlete should take 2 to 3 seconds to try to clear the letters before adjusting the chart to a slightly farther 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. 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 call out a letter on each successive chart correctly with the beat from the metronome.

Lens Rock

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 relaxed. Monocular lens sorting is a useful procedure

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.105-107 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 performance31-33 so that minimal attention is required for skilled performance. The work of Hebb108 and others109-111 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 that 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 follow the ball only 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 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. In addition, 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.

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, and so on) 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-the-last letter of each row, or other challenging saccade patterns. Multiple charts can also be used, with fixations moving in either 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,