The Eyes Have It: Vision and Movement Neurology
Vision = Priority 1
In optimizing health and performance, it is IMPOSSIBLE to overstate just how vital it is to have superior visual skills. Great vision is one of the most important, if not the most important, differentiators of mid-level athletes from great performers in virtually every sport and activity. The reason for this is very simple as a huge dependence upon vision is a part of our hard-wired survival makeup. Additionally, most researchers agree that 75-90% of most motor learning comes through the visual pathway at first. These factors make excellent vision priority #1.
Eyesight and Vision are Not the Same
“Eyesight is simply the ability to see something clearly, the so-called 20/20 eyesight (as measured in a standard eye examination with a Snellen chart). Vision goes beyond eyesight and can best be defined as the understanding of what is seen. Vision involves the ability to take incoming visual information, process that information and obtain meaning from it.”
- Dr. Donald Getz, OD
In other words, 20/20 is not enough! If they have given any thought to this at all, most instructors believe that if their client has “normal eyes” then that is good enough to permit performance on their activities. Unfortunately, nothing could be further from the truth! Normal 20/20 eyesight is only the beginning. Vision is a dynamic, powerful system that is often THE determining factor of movement excellence.
There are a number of different elements of visual skill – all of which play important roles in movement skills.
The Different Elements of Athletic Visual Skill
- Dynamic Visual Acuity – This is the visual skill that allows you to see objects clearly while the object is in motion. In virtually every sport this means that you need to have exceptionally good vision at distances ranging from a few inches to 300 feet.
- Eye Tracking – Refers to your ability to "keep your eyes on the ball," no matter how fast it is traveling.
- Eye Focusing/Accommodation – The skill to change focus quickly and accurately from one distance to another.
- Peripheral Vision – Allows you to see people and objects "out of the corner of your eye" while concentrating on a fixed point.
- Vergence Flexibility and Stamina – The ability to keep both eyes working together in unison under high speed, physically stressful situations and differing environments.
- Depth Perception – This skill allows you to quickly and accurately judge the distance and speed of objects moving toward and away from you.
- Imagery – This skill allows you to picture events with your "mind's eye" and your “virtual proprioception”.
- Sequencing – This refers to the ability to correctly see and “put in line” a series of stimuli. In other words, it refers to the ability to organize visual information which is a key skill to understanding and reacting to the events that occur in a sporting environment. Sequencing plays a role in virtually every sport.
- Eye-Hand & Eye-Foot Coordination – These crucial interactions are the ultimate basis of athletic skill. The ability to take in correct and appropriate visual information and translate it into necessary body movements is the essence of this skill set.
Vision Is Learned
Vision is learned. This makes vision a trainable skill. Almost anyone can be taught the necessary visual skills necessary to excel in sports and life. Plus, it stands to reason that since 75-90% of all learning comes through the visual pathway first, any interference in the visual system can interfere with reaching your client’s ability to reach their maximum potential.
Assessing Elements of Vision
To accurately assess the impact of vision on your client’s performance, there are four easy screening tests that you can use. Each of these tests looks at a different portion of the dynamic visual system. The tests are:
- PREP Test
- Eye Dominance
- Phoria Testing
- Suppression Testing
Postural Reactions to Eye Positions (PREP)
- Have the client stand quietly in a neutral stance with the elbows locked, arms lifted in front of the body, palms down, with thumb-side of the hands in contact.
- While keeping the eyes open, have your client keep the head still and move the eyes to the right and hold there for 10 seconds.
- Observe for any sway or rotation – particularly the FIRST movement your client makes.
- Repeat to the opposite side.
- Repeat moving the eyes up.
- Finally, repeat moving the eyes down.
- Repeat all of the above with the eyes closed.
In a normally functioning neuron-postural-control system:
- An eye shift to the right should create a slight right body rotation.
- An eye shift to the left should create a slight left body rotation.
- An eye shift up should cause the body to move into extension.
- An eye shift down should cause the body to move into flexion.
Use of the PREP test in this manner helps identify miscommunication and aberrant motor activity associated with eye muscle activity. In other words, it helps identify if certain eye positions are correctly facilitating correct movement patterns in the body.
Postural effects of extraocular muscle vibration.
Figure 2. Postural effects of vibration to the superior and inferior recti (Adapted from Roll et al 1989).
Figure 3. Postural effects of vibration to the medial and lateral recti (Adapted from Roll et al 1989).
Are you Right-Eyed or Left Eyed?
Just as you prefer one hand over the other, your CNS most likely has a dominant eye preference as well. According to research statistics, 2/3rds of the population is right-eye dominant. Additionally, approximately 80% of the population is what is termed same-side dominant. What this means is that you are right-handed and right-eyed or vice versa. It is possible, however, to be cross-dominant as well: right-handed and left-eyed or vice versa.
What is essential to understand about visual dominance is that it plays an important role in all movement performance. According to some researchers, your dominant eye processes information from 14-21 milliseconds faster that your non-dominant eye. Plus, your dominant eye provides your CNS with its “preferred” line of sight that tells you where things are in the world.
Determining Eye Dominance
There are a large number of simple tests for determining eye dominance. We will use this one:
- Extend both hands forward of your body and place the hands together making a small triangle (approximately 1/2 to 3/4 inch per side) between your thumbs and the first knuckle.
- With both eyes open, look through the triangle and center something such as a doorknob or the bullseye of a target in the triangle.
- Close your left eye. If the object remains in view, you are right eye dominant. If your hands appear to move off the object and move to the left, then you are left eye dominant.
- To validate the first test, look through the triangle and center the object again with both eyes open.
- Close your right eye. If the object remains in view, you are left eye dominant. If your hands appear to move off the object and move to the right, then you are right eye dominant.
Meet the Phorias – Ortho, Eso and Exo
Phoria describes a muscular condition of the eyes in one of three ways.
Esophoria is a muscle condition in which when both eyes are open each eye points accurately at the target. However, upon covering one eye the covered eye turns inwards. Also known as over-convergence.
Exophoria is a muscle condition in which one or both eyes drift outward. When both eyes are open each eye points accurately at the target. Upon covering one eye, the covered eye turns outwards. Exophoria usually is also known as under-convergence and can be associated with convergence insufficiency.
Orthophoria refers to a balanced condition in which the eye muscles maintain eye fixation when either eye is covered.
The Phorias in Sport and Life
Understanding what each of the phorias does can be critical to helping your clients more clearly “understand” what their vision is telling them.
For an esophore, because the eye muscles are pulling in, creating overconvergence, the world seems closer than it really is. In other words, what an orthophoric eye would see as 20 feet, an esophoric eye may see at 15 feet. The severity of the esophoria will alter the “distance gap” for each individual. In sports, esophores will have a tendency to miss shots, putts, baskets, etc by leaving them short of the target.
For an exophore, exactly the opposite is true. Exophores, who suffer from underconvergence see the world as farther away than it actually is. In sports, esophores will miss shots, putts, baskets, etc by overshooting the target.
Distance Makes the Difference
You may be both exo and eso dependent upon the distance you test at. This can cause significant visual difficulties with different tasks. The only way to know for sure is to perform the phoria testing at distances involving your athlete’s sport and then to train with the findings in mind!
An Interesting Tidbit
Highly exophoric individuals often fall asleep while reading because of the constant energy drain associated with holding the eyes inward. This can be extremely fatiguing. Also, some researchers state that 90+% of kids diagnosed with ADHD are extremely high exophoric.
Now that we have discussed the phoria’s, let’s test for them. A simple test to use is called the Alternate Cover Test. It can be used to quickly tell whether a client is ortho or if the client has a deviation. It is particularly useful in uncovering phorias because the technique does not allow the athlete to establish binocular fixation.
1) Either eye can be covered to start the test. Pause for 5-10 seconds with the cover in place over the eye to allow time for the eye to "drift" either in (esophoria) or out (exophoria).
2) Quickly move the cover to the other eye.
Pause again to allow the uncovered eye time to pick up fixation.
3) Quickly move the cover back to the other eye.
Pause again to allow the uncovered eye time to pick up fixation.
Repeat the procedure in a swinging fashion, observing the eye that is being uncovered.
Any movement of the recently uncovered eye to re-fixate on the target indicates that the athlete has a muscle imbalance. The direction of movement indicates the type of deviation (eso, exo).
Suppression – A Confused Brain
In case you have not yet realized it, we each have two eyes. When we look at an object, the retina of each eye forms an image of its own. Yet, when we look at an object, we do not see it as a double image because our brain processes the information from each retina and fuses them into one image.
Unfortunately, this fusion is possible only if the two images are almost similar in size and clarity. In other words, our brain cannot fuse two different images. The images on the two retina will be different if the visual acuity of the two eyes is vastly different, if one of the eyes is crossed, or if one of the eyes is a crossed eye (i.e., it has turned in or out, so that non-corresponding areas of two retina are stimulated).
In either situation, these different images create confusion in the brain. As a result, the brain will concentrate only on the better image available and ignore or suppress the other image: Hence the name suppression.
What is interesting here is that, in most cases, the suppressed eye can perform by itself when necessary. This generally means that this condition is not caught in any eye exam in which the eyes are alternately covered. The brain is so good at suppression that the athlete with this condition is often unaware that he is not seeing with both eyes together.
The vision of a person with suppression in one eye could be thought of as one dimensional. He often suffers from less than optimal depth perception, finding it very difficult to correctly judge the location of objects in space
If suppression is not corrected or treated in time, the suppressed eye gradually loses its power of seeing and becomes amblyopic. An amblyopic eye is a lazy eye which cannot be fully awakened (i.e., its vision cannot be corrected) even with appropriate glasses.
Suppression Testing Procedure
For this test, you will use a 12 foot thin rope (or string) with 3 beads or buttons placed as directed. If your client wears glasses you will do the test first with the glasses off and then with the glasses on.
(1) Tie one end of the string to a door-knob. Place beads on the string at distances of six inches, eighteen inches and four feet from the door-knob.
(2) Stand twelve feet from the door-knob. Hold the string taut against the tip of your nose.
(3) With both the eyes, look at the hole of the bead closest to you.
(4) You should see two strings, crossing exactly in the button-hole [see diagram below].
(5) Work to direct both your eyes exactly at the center of the button-hole.
(6) Note your findings accordingly:
- Are both the strings visible?
- Is one string less distinct than the other? Which one?
- Is one of the strings only partially visible? Which one?
- Does one string disappear completely? Which one?
(7) Repeat the routine with each of the remaining buttons on the string.
Evaluation of Suppression Test Results
If the whole lengths of the two strings are clearly visible and they cross at the button-hole you are looking at, both your eyes are seeing simultaneously and there is no suppression.
If one of the two strings is less distinct than the other or if one of the strings disappears partially or completely, the vision of one of your eyes is being suppressed by the brain. Suppression of the right eye is indicated by indistinctness or disappearance of the left string and vice versa. Just indistinctness indicates mild suppression, partial disappearance indicates marked suppression and total disappearance indicates total suppression of the vision of a particular eye.