Dynamic Visual Acuity: Eye Biomechanics

Did you know that there is only one human activity which taxes dynamic vision skills more than tennis?

The answer will amaze you and should play a role in your choice of eye protection/sunglass products for tennis. Understandably, few sunglass manufacturers produce product which has the necessary visual accuracy that tennis demands.  The task of watching a small ball go from optical infinity to reading distance on such a continuous basis is enormously difficult for the visual/motor system.  Pictured below is the miraculously complex visual system with only a couple of its nearby muscles.  Don’t forget the brain needs training to interpret what this system sends it, then a call to action is initiated, then the muscles in the rest of the body try to comply!

As background, “static vision skills” are those tested by a typical Optometrist. They are used to read efficiently or see objects clearly at a variety of distances. For example, though this page does not move, your eyes have still learned to recognize the letters, comprehend their meaning, and move smoothly from line to line. A set of skills that can be improved if desired. The movement in these “static” movement skills are related to those required for tennis.

“Dynamic Visual Acuity” is a more complex set of occular muscle skills needed to track moving objects efficiently.  Only a handful of eye care professionals are trained in evaluating these skills in the United States. Even fewer have the experience to improve these skills predictably.  For the actual list of eye skills used in SVT, see the original research below called, “Visual Skills of the Human Eye”.

Amazingly, even the most skilled athletes can improve their visual skills with highly specialized and supervised computer exercises. Dr. Polan even guarantees improvement in batting percentage for baseball players! For more information on his incredible work, go to: http://www.DrGaryPolan.com

The key to understanding this new science is that: ALL VISUAL SKILLS ARE LEARNED, NOT INHERITED!

Q.  So, what is the most challenging human activity to the “Dynamic Visual Acuity” skills for the eyes?  Even more than tennis?  A.  Jet Fighter Pilot!

Original Research

Visual Skills of the Human Eye

by Jonathan Bailin, Ph.D. & Dr. Gary Polan, O.D.
Exercise Physiology/Biomechanics/Ergonomics
Sports Medicine & Ergonomics Associates

Submitted in 1997

The author has collaborated with his associate, Dr. Gary Polan, O.D. many times.  Dr. Polan is a pioneer in the field of Sports Vision Training (SVT) and/or Vision Training (VT) since 1984 (*).  In 1996, his work received corroboration by the staff at the Jules Stein Eye Institute at the UCLA Medical School (**).  Here, we will outline all the individual skills required by the visual system to perform at its peak that now form the science of VT and SVT.

Dr. Polan’s experience in training and improvement of visual skills has resulted in “surprising” advances in most learning disabled cases.  Improvements in intellectual activity which are generally unexpected, but very welcomed by parents, have not been well documented by rigorous research designs to date.  Still, we are confident that a product like Sportwall will play a significant role in improving reading skills, Attention Deficit Disorder (ADD), and Dyslexia.

Few realize that reading is a motor activity like sports!  Just one of the many common reading flaws is transposing letters like “ea” to “ae”.  When the number or severity of flaws effects performance or comprehension, VT or SVT is warranted.

So, before any improvement in reading or athletic performance can take place the visual system must be engaged.  What are the exact skills that the eyes posses that can influence performance?

Introduction to Visual Skills

First, readers of this proposal should realize that ALL visual skills are learned. From infancy, the vision skills that we take for granted have been built gradually over time.  Contrary to folklore, the are not precisely genetically predetermined and can be improved.

Fact:  visual skills, no matter how polished by a our activities or sports, can be improved in a clinical or private practice setting.  Sports careers, worth millions of dollars, can be improved and lengthened past their usual expirations.  One of Dr. Polan’s more famous patients Carl Lewis, says that more of his records would still be standing today had he experienced SVT during his competitive career.

Visual skills can be divided into 3 sub areas: Visual Acuity, Visual Efficacy, and Visual Processing. Visual Acuity is measured by standard optometric tests commonly used for eye prescriptions including standard eye chart examinations.

Visual Efficacy can be measured by testing among the 24 areas listed below which include focusing, convergence, divergence, etc. Visual Processing can be evaluated by tests which measure the extent of learning disabilities such as Reading Disorders, Attention Deficit Disorder (ADD), and Dyslexia as found in items 2, 7, I5, 16, 18, 20, 21, 22, and 24. Most ADD and Dyslexia is responsive to treatments for visual/perceptual deficiencies in these areas of training thus often diminished or alleviated completely.

Visual Efficacy Skills

All movement mechanics during sports are enhanced by eye skills and eye health.  In turn, improvements in several areas of eye skills will enhance eye performance during motor activity.  For example, reaction time is first dependent on the visual accuracy and recognition skills listed.  To acquaint the reader with the proposed research, a brief review of each eye skill which can positively effect motor performance must be considered.  Please note that Visual Efficacy Skills are a subset of all the visual skills listed below.


1) Visual Acuity-your ability to achieve a sharp resolution of an image can be divided into static acuity (stationary images) and dynamic acuity (resolution of images in motion).

Static Visual Acuity–Corrected or not, your eyes should have 20/15 vision for high speed activities. “20/15” vision means that is you see at 20 feet what the average person only sees accurately at IS feet away.

Dynamic Visual Acuity–the ability to see sharply while the player, opponent, and ball are all in motion. This ability is made up of many other skills such as Convergence, Focusing, Tracking, and Interpretation, etc. Following the action with the eyes rather than the head or body is more efficient and puts less stress on the balance and muscular-nervous system.

2) Visualization—is the ability to plan, imagine, and prepare for upcoming motor skills and movements.  Some sports scientists believe visualization of needed skills is more efficient than coaching “pep talks”.

3) Peripheral Vision–is critical to awareness of other important things while watching the ball such as your teammates, boundaries, or opponents.

4) Depth Perception—is the ability to quickly and accurately judge the distance between yourself and your opponent, teammates, targets, and boundary lines while judging the speed, rotation, and flight path of the ball.  Billy J King rates this above court speed and eye-hand coordination for junior tennis players.  Quickly diminished by those who stare during the day-students, programmers, and executives may play poorer tennis during the week than week end for this reason.

5) Visual Pursuit—is the ability to use the eyes to follow a moving object smoothly and accurately. This critical skill is based on good eye teaming and eye muscle balance but it cannot track a ball smoothly at high speeds where Saccadic Movement takes over.

6) Saccadic Movement-is the ability of the eyes to “jump” from one point to another when speeds exceed those of visual pursuit. This skill is used in reading to jump from one word to the next. If this skill is poor, reading ability is affected!  Quick, accurate saccades are used to survey rapidly with as little head movement as necessary. Head movement is a less efficient method of eye tracking and can confuse balance.  Unnecessary head movements, and eyelid reflexes to flinch, must be overcome with training.

7) Visual Concentration-describes the cooperation between Visual Pursuit, Saccadic Movement, and Visualization in the “minds eye” or imagination. This skill is not scientifically well defined yet, but is exemplified by tennis players who must switch concentration rapidly from target, to ball, to processes of planning and prediction which are critical to performance.

8) Speed Of Focusing-is the ability to shift focus from near, intermediate, and far distance. This eye muscle skill is subject to the same fatigue which affects other muscles over the course of exercise.

9) Glare Recovery Speed-is the ability to see clearly after looking toward intense light. Focusing near sun, and at tennis court lights, causes “dazzle” to the retina.

10) Sight in dim illumination.

11) Eye Muscle Stamina-is the ability to withstand fatigue without decreased performance in a variety of eye tasks.

12) Color Perception—is not critical but may play a role in optic yellow against white lines and line calls.

13) Eye Dominance—is the ability of the sight in one eye to dominate images from the other.  Tennis players generally prefer strokes on the same side as the dominant eye which is usually the right, for right handed players, over 80% of the time.

14) Fixation Ability-is the skill of preventing eye fatigue which comes from staring at objects too long. Receivers with poor fixation skills fatigue within a few seconds of staring at the server.  Other players do not, but staring should be avoided.

15) Visual Memory—is the accumulation of past experiences such as the number of proper swings logged in a players “motor program file”. This combined with visualization for future swings is probably a major factor in consistency during competition. Visual memory fades with time.

16)  Spatial Localization-Knowing your position relative to other objects especially while you, ball, and opponent are moving.

16a) Esophoria—players who see the world CLOSER than reality, tend to hit/throw shorter.

16b) Exophoria–players who see the world FARTHER than reality, tend to hit/throw longer.  We believe Shaquille O’Neal was a good example of this.

17a)  Speed of Recognition Time-is how fast can you identify images.

17b) Reaction Time–How fast can you react to those images.

18) Eyes to Body Coordination–is the ability to integrate what you see into an appropriate and coordinated response from your body parts (aka: Visual/Motor Integration).

19) Contrast Sensitivity—the ability to pick out an important object against a field of other objects.

20) Visual Attention-is the skill used to prepare the eyes and brain which heightens its readiness for an upcoming task. This is a precursor to Visual/Motor Organization.   Of course, the body can influence this system which is one reason why elite tennis players bounce during the opponents contact.

21) Figure/Ground–is the ability to pick out an object in the foreground against a variety of background fields; to discriminate the figure to be attended to and to see the interrelationships to its background information.

22) Visual/Motor Organization–is the ordering and organization of motor skills; to choose from a “catalog” of motor programs for meaningful and productive action.

23) Jump Duction–the ability to move from visual tasks that require convergence to divergence of the eyes and back.  Jump Duction deals with vergence; the activity of the extraocular muscles to diverge for distance, and converge for near objects rapidly and efficiently.

24)  Auditory/Tachistoscopic Skills— are those which help sound and sight skills complement each other during visual processing. It is the auditory/visual integration ability of an individual which coordinates inputs into a meaningful perception and to shift priority and attention from one to the other when necessary.  Years ago, preventing air traffic over the US Open tennis tournament in New York was initiated for this reason.  Players had to hear the serve as well as see it.

Auditory specialists can better assess the ability to discern background from foreground sounds similar to the way we will assess background to foreground objects. This is an area worthy of much more study. There is much potential to design audio triggers, cues, and scoring tones here.  Consider the bell for a horse race!


The list of “Visual Skills” above items 1-24 is Copyright (c) Jonathan Bailin. Ph.D. 1997. Reproduction by author’s permission only.

* Hoflinan, L., Polan, G., Powell, J. The relationship of contrast sensitivity functions to sports vision” Journal of the American Optometric Association 55:10,747-752, Oct 1984.
** Laby, Rosenbaum, Kirschen, Davidson, Rosenbaum, Strasser, Mellman “the visual Function of professional baseball players” American Journal of Opthalmologv 122:4,476-485. Oct. 1996.

Keywords:  sports vision training, SVT, vision training, VT, eye skills, reading skills, sports performance, sports career enhancement, visual acuity, visual efficacy, motor learning, eye performance, eye health

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