CLINICAL

  sports vision

Sports Vision Instrumentation and Tests

A rookie’s guide to evaluating and training athletes’ visual skills.

GRAHAM ERICKSON, O.D., FOREST GROVE, ORE.

Optometrists who wish to provide specialized vision care to athletes must identify the vision skills essential to successful performance and the methods to evaluate the quality of those skills.

The most successful athletes often have visual abilities superior to lower-level or less successful athletes. Helping athletes to improve their visual skills, thus bettering their ability in their sport, benefits your practice by enhancing the services provided to those in your community who want to address their avocational pursuits. In addition, these services give you the opportunity to connect with a part of your community that does not often seek vision care.

Here, I discuss the appropriate methods of assessing and training athletes in the visual performance skills commonly identified as correlating with success in sports.

Evaluation

To provide specialized vision care to an athlete, the optometrist should first identify the vision factors essential to successful performance of the sport. There is a significant body of research comparing performance on various measures of visual function in athlete populations to guide the clinician in selecting appropriate visual measures. A sport-specific evaluation identifies areas of visual performance strengths, as well as areas of opportunity to improve performance.

Here are the important visual skills you should consider measuring:

▸ Static visual acuity (SVA). Measurement of SVA typically begins the assessment of visual performance skills. Compromised SVA (below average compared with a group of similar athletes) can negatively affect most other areas of visual performance (such as those listed throughout the rest of this article). A chart system with 20/10 or better as the best acuity measurable is needed to determine the true threshold for the athlete. In some sports, such as baseball, 20/20 VA is below the average found for this population.

The Howard-Dolman device allows for the assessment of real-object stereopsis as well as measurements in different positions of gaze.

▸ Dynamic visual acuity (DVA). DVA is generally defined as the ability of the visual system to resolve detail when there is relative movement between the target and the observer. As most sports involve extensive movement of an object (ball, puck, etc.), competitors, teammates and the athlete — sometimes all simultaneously — a DVA assessment provides valuable information. NeuroCom’s inVision system provides this assessment.

▸ Contrast sensitivity (CS). Most sports involve interpreting visual information at contrast levels below that measured by a typical visual acuity chart. CS is important to athletic success because it measures the visual system’s ability to process spatial or temporal information about objects and their backgrounds under varying lighting conditions.

Many commercial systems are available to measure CS. Some use linear grating patterns, while others use letters or numbers. The CS system you use to evaluate athletes should allow for the determination of a threshold contrast level at specific spatial frequencies or acuity demands. O.D.s can easily research these systems online or at exhibitions and trade shows.

▸ Stereopsis. Determining distance and spatial localization of an object is a necessity for athletes in many sports, including baseball, football, basketball, soccer, hockey, golf and tennis. These judgments can be made using monocular depth cues, but it is suggested that superior binocular depth perception, or stereopsis, can be advantageous for athletes.

An evaluation of stereopsis at a distance of 3m or farther is recommended. Since sports require depth judgments of real objects, a procedure that measures real depth, rather than simulated depth, is preferred. The Howard-Dolman device allows for the assessment of real-object stereopsis, as well as measurements in different positions of gaze. Several other simulated stereopsis tests are available.

▸ Accommodative vergence facility. Competitive sports rarely occur at one distance. Most athletes must look at far, intermediate and near distances quickly, requiring rapid accommodative-vergence responses.

This visual skill can be assessed with the Haynes Distance Rock Test. This is the only test that uses standardized charts at two different distances (40cm and 6m), with fixation rapidly alternated between the two charts. This type of near-far assessment more closely simulates real-world accommodative vergence facility, rather than the use of either lenses or prism that separate the accommodative and vergence demands.

▸ Central eye-hand/eye-foot reaction and response time. Visual-motor reaction and response speeds are critical to athletes’ 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.

In sport, reaction time is analogous to quickness to take the first step, and response relates to speed once a response has been initiated. For example, two football players may respond to a fumble in football; the one with a faster reaction time will act first, while the one with faster response performance will cover the distance to the ball in less time.

The Multi-Operational Apparatus for Reaction Time (MOART) system provides programs to measure simple, choice and complex reaction times with either hand or foot responses.

▸ Peripheral eye-hand response. The overall ability to process and respond to peripheral visual stimuli is a common element of dynamic, reactive sports, such as hockey. Many commercially available instruments can be used to evaluate this skill area, including BATAK Pro, Dynavision D2, fitLight Trainer, Sanet Vision Integrator (HTS), Sports Vision Trainer (SVT), Vision Coach, Vision Motor Enhancement Training (Bernell) and Wayne Saccadic Fixator. The instruments commonly test in two modes: (1) visual proaction time, a self-paced mode and (2) visual reaction time, an instrument-paced stimulus presentation.

▸ Visual coincidence-anticipation. This is the ability to predict the arrival of an object or stimulus at a designated place and is usually measured with motor response. Theoretically, visual coincidence-anticipation timing contributes to the ability to catch or hit an approaching ball.

The Bassin Anticipation Timer (Lafayette Instruments) and the Wayne Speed-Trac are commercially available devices for measuring visual coincidence anticipation. These instruments consist of tracks of LEDs that can be sequentially illuminated down a track in rapid succession to simulate the apparent motion of a rapidly approaching stimulus. The velocity of the stimulus lights can be calibrated to simulate the action speeds encountered in the athletes’ sport, resembling the stimulus parameters experienced by the athlete (e.g., the pitch speeds in baseball).

Training

You can take many approaches to selecting training procedures, from generalized programs administered to every athlete, to precise, diagnosis-specific and task-specific individualized programs. Each sports vision practitioner develops the approach that best suits their mode of practice.

Here are some commonly used procedures, though these do not represent all training procedures.

▸ Visual sensitivity. The primary goal is to improve the athlete’s ability to discriminate subtle detail in the sport environment. Common visual sensitivity training procedures include emphasis of blur discrimination by using Bangerter occlusion foils (Fresnel Prism and Lens Co.), fixation stability by using a Haidinger’s Brush (Macula Integrity Tester, Bernell) or contrast sensitivity (UltimEyes app or RevitalVision computer-based training).

▸ DVA. Targets can be placed on a rotating disk, such as the Wayne Robot Rotator or Rotation Trainers, to enhance the sensitivity of visual discrimination while the targets are in motion. The Wayne Tachistoscope Rotator Scanner is composed of two prisms that can be rotated in front of a Perceptamatic tachistoscope lens. Images can be presented for a brief duration, facilitating the training of short-exposure DVA. For home-based training, instruct patients to use a pitchback, or ball machine, along with soft baseballs with markings. Athletes attempt to locate and identify the markings on balls as they come toward them.

▸ Eye movements, accommodation, vergence. Many activities developed for vision therapy can be modified to simulate the visual demands of sport, such as Brock strings, vectograms, tranaglyphs, lens and prism flippers and Marsden balls. Several companies offer such training tools and charts.

▸ Speed of perception. Tachistoscopes have been used to enhance this ability for a variety of tasks, and many computer-based programs (such as PTS II iNet and Computer Aided Vision Therapy) can be modified for use in training. A strobe light or stroboscopic filters (Primary Strobe Glasses, Appreciate Co.) provide another method for the development of visual information-processing speed. The athlete is encouraged to maintain performance of a sport-related activity with progressively less visual information as the flash rate on the strobe is reduced. This activity provides an effective method to develop better visual processing of information directly related to essential skill training for their sport.

▸ Eye-hand/foot/body-reaction speed. The instruments discussed above in the evaluation section for these skills are useful for training purposes as well. Each can be used for a variety of effective training programs.

▸ Coincidence-anticipation. The Bassin Anticipation Timer and Wayne Speed-Trac for evaluation of these skills are also useful for training purposes. Additionally, strobe training can be used to develop this skill area.

Win the day

A practice that has instrumentation to evaluate and train visual performance can boost its revenue while helping to establish a reputation for sports vision services. OM

See the online version of this article for a list of sports vision equipment and instrumentation suppliers.

Dr. Erickson has served as past-chair of the American Optometrie 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. Send comments to optometricmanagement@gmail.com.