Give Athletes Better Vision Shot a at Better Vision

Whether they shoot foul shots or target rifles, your athletic patients require the best vision to stay at the top of their game.

By Graham B. Erickson, O.D.

Goal Statement:

Optometrists can provide targeted visual assessment, unique refractive options and even sports vision training to help athlete patients achieve peak performance. This article examines the visual skills that are most pertinent to your athletic patients, as well as reviews the best vision-correction options for athletes who participate in a variety of different sports.

Faculty/Editorial Board:

Graham B. Erickson, O.D.

Credit Statement:

This course is COPE-approved for 1 hour of CE credit. COPE ID is 34635-GO. Please check your state licensing board to see if this approval counts toward your CE requirement for relicensure.

Joint-Sponsorship Statement:

This continuing education course is joint-sponsored by the Pennsylvania College of Optometry.

Disclosure Statement:

Dr. Erickson is a paid consultant to Nike, Inc.

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Good vision is a critical factor in sports performance, because visual information is the dominant sensory system when performing practically any perceptual-motor task.^1-4 Some researchers contend that athletes possess superior visual systems that allow them to see and process critical visual information more effectively than "non-athletes" and novice athletes.^4-7 Others, however, argue that athletes do not possess superior visual system physiology, but that elite athletes are able to use available visual information more efficiently than novices in a competitive sports environment.^8-10

In either case, optometrists can provide targeted visual assessment, unique refractive options and even sports vision training to help these patients achieve peak performance.

Here, we'll examine the visual skills that are most pertinent to your athletic patients, as well as discuss the best vision-correction options for athletes who participate in a variety of different sports.

What is Sports Vision?

The term "sports vision" has been used to describe a host of eye care services that are provided to athletes. Practitioners working in this area usually are involved with one or more of the following professional activities:¹¹

• Prevention and management of sports-related eye injuries.
• Assessment and remediation of functional vision deficiencies that may negatively impact competitive consistency.
• Specialized contact lens services with emphasis on environmental factors in sports, position of gaze factors, emergency care and attainment of maximum visual acuity.
• Performance-based ophthalmic eyewear services that address visual and environmental demands.
• Assessment of specific sports-related visual abilities.
• Enhancement training of specific visual abilities that are considered to be essential for competitive consistency in a specific sport activity.
• Consultation with athletes, coaches, trainers and teams regarding visual factors and strategies related to consistent peak athletic performance.

Most of our patients are active participants in sports or recreational activities, and many of these individuals are dedicated to the pursuit of athletic excellence. A critical, but often neglected, aspect of peak human performance is optimal visual function. So, all optometrists must consider visual performance factors when providing one or more of the aforementioned services to athletic patients.

Evaluation of Visual Performance Skills

The vision and visual perceptual skills identified as important for sports performance include: static and dynamic acuities, contrast sensitivity, distance stereopsis, accommodative-vergence facility, span of perception, central eye-hand reaction and response speeds, and peripheral eye-hand response speed.^11,12 Two extensive review articles concluded that athletes have demonstrated better visual abilities than non-athletes, and that top-tier athletes--those who are most successful--often have visual abilities that are superior to lower-level or less successful athletes.^5,6 Some aspects of these skills commonly are assessed as part of a routine vision exam, but many vision skills are not evaluated for various reasons (e.g., there is little or no standardization of assessment procedures and/or limited or outdated diagnostic instrumentation).

To effectively provide specialized vision care to an athlete, you should first identify which vision factors are essential to successful performance in the individual's sport(s) of choice.^12,13 For example, a dynamic and reactive sport, such as basketball, has very different visual demands than the static precision requirements of target shooting. The vision assessment should then include methods to evaluate the quality of those skills in the most appropriate, accurate and reproducible manner. The following visual skills have been frequently identified as important across many sports disciplines:

*Static visual acuity (SVA). Assessment of visual performance skills routinely begins with a measurement of SVA. Compromised SVA can negatively affect other areas of visual performance.¹¹ Previous research has found mixed results regarding SVA in athlete populations.

For example, when SVA is assessed using chart systems (with 20/20 as the best acuity measureable), there is no statistically significant difference in the visual ability of athletes compared to non-athletes.^14-16 Even when a best acuity demand of 20/15 is presented, one study found that 81% of professional baseball players could achieve that level.¹⁷ The researchers subsequently modified their assessment method to achieve acuity demands down to 20/7.5, reporting overall mean SVAs of approximately 20/13, with several athletes exhibiting SVAs of 20/9.2 or better.¹⁷

*Dynamic visual acuity (DVA). DVA generally is defined as the ability of the visual system to resolve detail when there is relative movement between the target and the observer.^6,11 Many sports involve extensive object movement, including balls, pucks, competitors, teammates, etc. Often, at elite levels of sport, the velocity of movement between the athlete and the target is tremendously high, so athletes need to accurately perceive and identify critical target features during dynamic situations.

One literature review indicated that athletes demonstrate superior DVA abilities compared to non-athletes, and that elite athletes have better DVA than amateur or non-elite athletes do.⁵ This suggests that there is an important link between elite athletes and DVA ability.

On the other hand, a separate report documented no significant differences in performance on a DVA test between elite and sub-elite youth soccer players.¹⁸ (However, their use of a predictable rotator device to measure this function may not have been environmentally appropriate to simulate the visual task demands of a dynamic, large-field sport such as soccer.) Although many researchers agree about the importance of DVA in sports, this visual skill often is not assessed in clinical practice due to limitations in available commercial instruments.⁶

*Contrast sensitivity (CS). CS measures the visual system's ability to process spatial or temporal information about objects and their backgrounds under various lighting conditions. Measuring an athlete's CS is important because most sports involve interpreting visual information at contrast levels below what is measured with a typical visual acuity chart.¹¹ Performance of athletes on CS testing is significantly better than non-athletes across all spatial frequencies evaluated.^11,19,20 CS may be improved or degraded with contact lens wear or refractive surgery.

Many commercial systems are available to measure CS.¹⁶ Several devices use linear grating patterns that vary in spatial frequency, contrast level and, possibly, orientation. Others use letters or numbers of different contrast levels and/ or sizes. CS measurements usually involve determination of a threshold contrast level at specific spatial frequencies, and reduced sensitivity may relate to performance inconsistency in some sports.

* Stereopsis. Determining distance and spatial localization of an object is a necessity for athletes in many sports. While these judgments can be made using monocular depth cues, superior binocular depth perception is more advantageous for an athlete.²¹

Research on the assessment of stereopsis has produced mixed results; some studies found no difference between athlete and non-athlete populations; whereas, other studies found better performance in athletes.^11,17,21 The difference in these findings may be due to the lack of standardized testing procedures, the use of simulated depth targets, and the limitations of the instruments to measure threshold stereoacuity.⁶

Previous studies employed near stereo tests or testing at far with vectographic projection slides or a Howard-Dolman apparatus.¹¹ Considering that many sports are dynamic, athletes would likely perform better with a dynamic stereop-sis assessment, because static testing may not reveal much difference between athletes and non-athletes.

* Accommodative-vergence facility. Competitive sports rarely occur at one distance. Most athletes need to look between far, intermediate and near distances extremely quickly, requiring rapid accommodative-vergence responses. This visual skill can be assessed using "distance rock testing." A study using this test presented normative data for a population of elite athletes, but did not compare performance with that of non-athletes.¹¹

* Perception span. Perception span, or central visual recognition accuracy, uses tachistoscopic presentation to measure the speed and span of recognition. Several studies have investigated speed of recognition abilities in athletes who play baseball, cricket, volleyball, tennis and other "fast ball" sports.^22-25 Most studies have found that experienced athletes can evaluate sport-relevant information more rapidly than inexperienced observers.^22-25

Other studies have investigated both the speed and span of recognition by evaluating the ability to recall a sequence of numbers presented tachistoscopically for 1/50 of a second and found no difference in athletes compared with non-athletes.^11,14

However, one particular report found significant differences in performance for both span and speed of recognition, which were also present when distraction factors were added to simulate competition conditions.²⁶ When considering these differences in research results, it indicates that the use of numerical stimuli may confound the assessment of recognition speed in athletes.²⁶

Thus, the use of target parameters that more closely simulate the visual information processed in sport situations can yield better discrimination of perception span abilities that correlate with sports performance.²⁶

* Central eye-hand reaction and response time. Visual-motor reaction and response speeds are critical to performance. Reaction time is the elapsed time between the onset of a visual stimulus and the initiation of a motor response. Response time is the total time required by the visual system to process a stimulus plus the time needed to complete the motor response.

Several studies report that athletes in various sports have faster reaction times compared to non-athletes, and that reaction time is a discriminator between expertise levels.^27-30 However, other studies have not reproduced this difference.^31,32 A gender bias also has been reported, with males achieving faster times than females on average.^11,33

Interestingly, eye-hand reaction time can be improved with brief training regimens, making this a potentially valuable assessment and/or goal for the athlete.¹¹

* Peripheral eye-hand response. Overall ability to process and respond to visual stimuli strongly enhances an athlete's eye-hand coordination.⁶ The typical instrumentation used for evaluating eye-hand coordination has been a two-dimensional panel with an array of lights mounted on a wall, such as the Wayne Saccadic Fixator (Wayne Engineering). When using this device, the athlete is required to press a randomly lit button as rapidly as possible with one hand. Then, another button is lit in a random position on the instrument and the reaction time reflex cycle is repeated for the selected test time period. The panel is set at the athlete's arm length and is larger than the central visual field, thus assessing a peripheral eye-hand response.

The Wayne Saccadic Fixator is typically programmed to test in two primary modes: visual proaction time (a self-paced mode for a set time period in which each light remains lit until the button is pressed, then the next random light is lit); and visual reaction time (an instrument-paced stimulus presentation in which each light stays lit for a preset amount of time [0.75 seconds] before automatically switching to another light, whether or not the button is pressed).

One study found better visual proaction times in youth athletes than non-athletes, while another study found no such difference between adult athletes and non-athletes.^14,34 Visual reaction time has been compared in both athletes and non-athletes in only one study, in which athletes performed better than non-athletes.¹⁴

Nike SPARQ Testing

The Nike SPARQ Sensory Training Station is designed to test vision skills that previously have been identified as important for sports, including SVA, DVA, CS, distance stereopsis, accommoda-tive-vergence facility, span of perception, central eye-hand reaction and response speeds, and peripheral eye-hand response speed. It is designed to provide a customized "sensory performance profile" that graphically represents the athlete's visual strengths and weaknesses by comparing performance to a database of peers. Each profile presents the top four opportunities for intervention and/or enhancement based on performance. For example, if measurements of visual acuity and CS are reduced, a comprehensive eye exam is recommended.

The results of one study indicated that many of the Nike SPARQ Sensory Training Station assessments demonstrate repeatability as well as no learning effect over time.³⁵ The measures that did improve across sessions (including accommodative-vergence facility, central eye-hand reaction and response speeds, and peripheral eye-hand response speed) demonstrated an expected learning effect due to the motor response characteristics being assessed.

Refractive Compensation for Athletes

Athletes who currently use vision correction require an evaluation to determine if the prescription is providing optimal visual performance for the specific sport demands. A task analysis of the sport will assist in determining the specific visual demands, and a careful refractive analysis can establish the best refractive compensation for use in that sport. For example, a myopic baseball player may benefit from an additional 0.25D of minus to improve contrast judgment or when playing in twilight conditions. Such prescriptions are sport-specific, and are not intended for general use.

Ultimately, you should continue the subjective refraction until the best visual acuity is reached. Do not stop the refraction at 20/20, because the athlete may be capable of seeing 20/10 or better. In some sports, such as major league base ball, 20/20 visual acuity is below average.^13,17 For many athletes, we need to raise the bar above 20/20 in order to provide optimal vision.

Guidelines have been published to assist the practitioner in determining when refractive compensation should be considered (see "Guidelines for Refractive Compensation in Athletes,").^12,36 Any patient with myopia of -0.25D or greater should be counseled on the possible benefits of refractive compensation (although correction of less than -0.50D is not available with contact lenses).

Guidelines for Refractive Compensation in Athletes
Refractive Status	Consider Prescribing at:
Myopia	-0.25D or more
Hyperopia	+1.00D or more
Astigmatism	0.50D or more*
Anisometropia	0.50D or more†
* Against-the-rule astigmatism and oblique astigmatism are more detrimental than with-the-rule astigmatism. † Consider meridional effects with asymmetric astigmatism.

 

Astigmatism has a similar effect on visual resolution, especially against-the-rule and oblique astigmatism. Refractive compensation should be considered with -0.50D or more astigmatism, although with-the-rule astigmatism compensation may not yield as much improvement on clinical evaluation.

Low amounts of hyperopia are often well tolerated without correction; however, hyperopia of +1.00D or greater may require a significant amount of effort from the athlete to achieve and maintain clarity. Judicious refractive compensation may reduce the accommodative effort needed for the athlete to achieve optimal image clarity. Low amounts of anisometropia are not always compensated for, especially when the refractive errors are low. Aniso-metropia of 0.50D or more can have a detrimental impact on depth perception, and some athletes may be sensitive to that effect.^5,6 Additionally, the effects of meridional anisometropia should be considered in athletes with asymmetric astigmatism.

Balancing the image quality through refractive compensation will enhance sensory fusion and improve the quality of spatial localization judgments. These guidelines are useful for the practitioner to trigger the discussion of the potential benefits of a refractive prescription. Ultimately, however, the athlete makes the decision whether to experiment with a prescription.

Contact Lenses vs. Spectacles

Spectacles are not commonly recommended for use in sports. The main concern is that most eyewear does not offer the impact resistance necessary to protect the wearer from the possible hazards encountered in many such activities. The American National Standards Institute (ANSI) performance standards for dress and industrial-strength (safety) eyewear are not applicable in most sports.

Instead, the American Society for Testing of Materials (ASTM) has developed performance standards for eye and head protection in many sports. ASTM performance standards are established for protective eyewear in each sport individually, and the forces potentially encountered in a sport are used to determine appropriate testing parameters.

Nike Ignites a SPARQ The Nike SPARQ Sensory Training Station consists of a single computer and two high-resolution LCD monitors (both 0.28mm dot pitch)--one 22-inch diagonal display and one 42-inch diagonal touch-sensitive display. A hand-held Apple iPod Touch is used in several assessments to measure responses. A liquid crystal shutter system creates simulated depth through a wireless link to the computer for stereopsis testing at far. Custom software controls the displays, input acquisition and test procedures, based on subject responses. Pre-recorded instructions are automatically played at the start of each assessment to maintain consistency for each evaluation.

 

Even if the athlete selects appropriate protective eyewear, consider the potential effects from optical aberrations of the lenses. Monochromatic lens aberrations can degrade the optical image transmitted through the off-center portions of the lens, and distortion can decrease the useful field of view through a lens. The reduction in the useful field of view can have a detrimental impact on performance in sports. For example, a right-handed tennis player viewing the ball toss during a serve looks through the left field portions of his or her spectacle lenses, and the image can be significantly altered by large refractive errors secondary to these aberrations.

On the other hand, field-of-view aberrations, visual field restriction, optical distortion, frame comfort, frame stability, surface reflections, lens fogging and precipitation issues with spectacle lenses largely can be avoided by moving the optics onto the cornea. Contact lenses eliminate the induced prismatic effects that are evident with most spectacle lenses. The potential visual field impediment created by eyewear frames also is eliminated with contact use, as are the issues of lens reflection and fogging that compromise visual performance with eyewear.

In comparison to spectacle use, the peripheral visual field is increased by approximately 15% with contact lens wear.² Contacts are an excellent vision-correction option for highly dynamic sports (see "Dynamic Reactive Sports,"), because no frame can be dislodged and no lenses can fog over. Although contact lens comfort is an obvious issue to contend with, frames pose significantly greater limitations for the majority of athletes.

Dynamic Reactive Sports
Baseball Softball Basketball Boxing Cycling Diving Fencing Football Gymnastics Hockey Kayaking Martial arts	Motor racing Racquet sports Skating Skeet and trap shooting Skiing Soccer Surfing Swimming Track and field events Water polo Wrestling Volleyball

 

Take note, however, that both target shooters and archers may actually prefer spectacles to contact lenses. The main advantage is the stability of clear vision obtained with spectacle lenses. Because peripheral vision is not a significant factor in most aiming sports, the enhanced visual field does not offer a significant benefit. The shooter or archer typically is not bothered by lens aberrations off the optical center. However, in athletes with strong prescriptions, the lenses may need to be fit with the optical centers set at the particular eye position used when aiming.

Hydrogel Lens Applications

Due to better comfort and stability, soft contact lenses typically are preferred to gas-permeable lenses for use in sports. The main considerations for hydrogel lenses are the material composition, water content, diameter and thickness. In general, lenses with a higher water content tend to dehydrate faster than low to medium water content lenses.³⁶ Therefore, thicker, low to medium water content lenses or silicone hydrogel lenses should be used for athletes who have dehydration problems.³⁶

Additionally, it has been suggested that the significantly increased oxygen permeability with silicone hydrogel lenses contributes to improved comfort and decreased symptoms of dryness. High water content lens materials or silicone hydrogel lenses may be needed for prolonged lens wear situations, in which oxygen transmission is a crucial factor. Larger-diameter lenses also are recommended for better stability and hydration.

These lens recommendations apply to sports in which considerable wind or airflow hits the athlete's face. Some endurance sports require a lens modality for extended use. In sports such as high-altitude mountaineering, long-distance sailing or long-distance motor racing, the athlete experiences extreme environmental conditions over an extended period of time, requiring excellent visual performance throughout the event while maintaining good ocular health.

Contact lenses for athletic use should fit more tightly than traditional fitting practices dictate. The lens should exhibit minimal movement after a blink as well as maintain a good centering position in extreme gaze directions.

Single-Use Lenses

Any athlete can benefit from single-use lenses--from the weekend athlete, who seeks the comfort of a disposable lens, to the professional athlete who prefers immaculately clean and fresh lenses before starting a competition and a quick replacement of lenses at any time during competition.

Single-use contact lenses can be a particularly useful for water sports. They offer an advantage over prescription masks or goggles, because peripheral vision is not as restricted. Nonetheless, you cannot overlook the main concerns regarding contact lens wear in the water-- namely lens loss and increased risk for microbial infection.

Orthokeratology

Orthokeratology is another option to reduce myopia and astigmatism with specially designed rigid lenses. What could potentially put an athlete at a disadvantage is the increased presence of higher-order aberrations and spherical aberration that may occur after initiating orthokeratology.^37,38

The increase of higher-order aberrations may cause a reduction in low-contrast visual acuity during the daytime, and this reduction is more significant in patients with larger pupil sizes.³⁸

However, orthokeratology remains an attractive option for athletes, especially young, myopic or astigmatic athletes who are not yet eligible for refractive surgery.

Visual Performance Training

Literature reviews have indicated that there is sufficient scientific support for the efficacy of vision therapy in modifying and improving visual system disorders.^4,12 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 result in demonstrable improvements in sports performance?

Several studies have reported positive effects of vision training programs on sports-specific tasks, while other studies have not identified improvement in performance.^39-43 The differences in study results are speculated to be caused by differing athletic skill levels (novice vs. expert subjects) and the use of general vs. specific vision training programs.¹²

Additionally, research design factors in all these studies weakened the results and conclusions, indicating the need for further study in this area of sports vision.

All the visual performance skills described here have been shown to be amenable to training.⁴ There are eye care professionals who provide this service. And, more recently, optometrists have collaborated with sports trainers to provide this service as part of personalized sports training. The sports trainers are taught the vision skill performance procedures similar to vision therapists, and are instructed to integrate these practices into the physical training program under the direction of the optometrist.

In this model, the athlete receives pre- and post-training assessments with the optometrist, making the O.D. part of the training team for the athlete. The Nike SPARQ Sensory Testing and Training Stations have digitized training programs for some aspects of visual performance, providing athletes the opportunity to train in eye care practices or at a sports training facility.

There is a vast array of refractive correction options available for athletic patients, and eye care professionals now have many new technologies to choose from in order to help meet the special demands encountered in athletic and recreational activities. We are uniquely suited to assist in the selection of the best eyewear designs, performance tints, contact lens parameters and protection for our athletes' eyes.

Additional vision training services to remediate and enhance critical visual performance factors should be discussed with the athlete as a management option. Most of the patients that we examine are routinely active in some sports and recreational pursuits. Not only do elite athletes reap performance advantages from our services, but patients from all walks of life can benefit from improvement in visual function across all aspects of daily life.

Once your reputation is established as an eye doctor who fulfills the visual needs of athletes, word-of-mouth marketing will bring a wealth of new athletic patients with vision care needs to your practice.

Dr. Erickson is a professor at Pacific University College of Optometry. He has served as past-chair of the American Optometric Association Sports Vision Section and the Binocular Vision, Perception and Pediatric Optometry Section of the American Academy of Optometry. He lectures both nationally and internationally on the topics of sports vision, pediatrics and binocular vision. Dr. Erickson is a paid consultant to Nike, Inc.

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