Ординатура / Офтальмология / Английские материалы / Relearning To See_Quackenbush_2000

align one eye with the near finger and the far finger. Also, some students mistakenly bring their attention to the near finger, instead of keeping the attention on the far finger. In fact, oftentimes the surprise of the two near fin­ gers causes some students to "jump" with their attention to the near finger. Of course, then there will only be one near finger, not two.

Although many students do not see the two near fingers initially, many see two near fingers in a very short time. Once the brain knows logically there can, and should, be two near fingers, both pictures are encouraged to "switch on." Note, however, the two near fin­ gers will most likely not be seen unless the directions, especially the alignments of the head, near finger, and far finger, are followed precisely. Ask someone to assist you with this if you are having difficulty.

The two near fingers form a "window" or "gate." Continuing to sketch the far finger, move the near finger straight out a few inches, and then back in to the original position. Notice that when the near finger moves out, the window becomes narrower; when the near finger moves closer, the window becomes wider. Return the near finger to the original 5-6 inches distance from the nose.

Continuing to sketch the far finger, notice there are two distant objects. In a-2, when sketcliing the far finger, one Dixie Man is seen slightly to right of the far finger (seen by the right eye), while a second Dixie Man is seen slightly to the left (seen by the left eye).

With two near fingers and two Dixie Men, we experience the fact that fusion only occurs at one distance, in this case, at the far finger. Two images of the far finger are being processed by the brain into one, fused far fin­ ger, as in "The Fused Finger," discussed at the beginning of this chapter.

The conscious experience of two fingers and two distant objects can be tiring. The mind knows there is only one near finger and one distant object in reality, yet sees two of each. Is seeing believing? The process of how we see the world is meant to be a subconscious activity. Usually, the brain ignores the fact that there are two images of an object at a distance other than where you are centraliz­ ing. You may want to rest before continuing.

Part В—Experiencing Fusion 1, The Near

Finger (or Yellow Pencil):

Refer to Plate 53: Fusion 1, Near Finger, b-i, and Fusion/Near Finger, b-2.

Aligning the head, fingers, and distant object as in Part A, now sketch the near finger. The area of centralizing is indicated by the small circle. There should be one solid near finger and two semi-transparent far fingers, and two distant objects. The two images of the near finger are now fused into one near finger.

If the head, near finger and far finger are correctly aligned, the near finger will be exactly in the middle of the two far fingers. (The two far fingers should also be in the mid­ dle of the two distant Dixie Men.) Notice again how fusion only occurs at one distance, in this case, at the near finger.

Unlike the experience in Part A, the left far finger is now seen by the left eye, and the right far finger is seen by the right eye. You can check this fact by alternately closing or covering one eye at a time. Remember to continue sketching the near finger.

Part С—Experiencing Fusion 1, The Distant

Dixie Man:

Refer to Plate 53: Fusion 1, Dixie Man, c-i, and Fusion/Dixie Man, c-2.

Aligning the head, fingers, and distant object as in Parts A and B, sketch an object straight ahead, far into the distance (Dixie Man).

There should now be four fingers The near finger creates a wide window (or gate), and the far finger creates a narrow window (in the center of the wide window). One Dixie Man should appear exactly in the center of both the wide and narrow "finger" windows. The two images of Dixie Man received by the eyes are now being fused into one image by the brain. Unlike a-2 and b-2, notice how there is now only one boat.

Parts A, B, and С—Experiencing Fusion i:

Now, shift between the distant object, the far finger, and the near finger, spending a few moments sketching each one. Notice again how fusion only occurs at one distance at a time—at the point of centralizing. The other two objects not being sketched are double.

Notice also how there is a "time delay" between shifting your attention from one fin­ ger to the other finger to the distant object. First, the mind chooses to shift to a different object. Then the messages are sent from the brain to the eyes. Finally the eye muscles con­ verge and accommodate to the new object of interest. The mind is primary and the physi­ cal is secondary.

You may be able to feel the convergence of the eye muscles by repeating this experi­ ence, imagining shifting back and forth between the distant object and your finger with your eyelids closed.

Vision is primarily a mental function. Bates discovered that mental strain sends messages of imperfect sight to the eyes, while mental relaxation sends messages of normal sight to the eyes

FUSION AN D D O U B L E IMAGES E X P L A I N E D FURTHER

Fusion is the merging, or combining, of the two pictures seen by the two eyes into one image. Fusion occurs in the brain, and at only one distance. There is one "fused" object at our point of interest, i.e., where we central­ ize. Fusion is possible only when there is binocular vision.

Convergence is the alignment of both eyes to a single point of interest (centralization). This alignment extends from the point of interest, through the eyeball, and into the fovea of each eye. The eyes are said to be con­ verging, or intersecting, at that particular point of interest.

In most cases, fusion occurs automatically as a result of normal convergence.

In Plate 5 3 : Fusion 1, Far Finger, a-i, and

Fusion/Far Finger, a-2, the eyes are correctly intersecting on the far finger, creating one "fused" far finger. From the right eye's point of view, the near finger appears to be located to the left of the far finger; from the left eye's viewpoint, the near finger appears to be located to the right of the far finger. If both pictures remain "on," the brain has no option but to produce two images of the near finger while sketching the far finger.

For the right eye, Dixie Man appears to the right of the far finger; for the left eye, Dixie Man appears to the left of the far finger. Again, the brain has no option but to pro­ duce two images of Dixie Man while sketch­ ing the far finger.

The correct experience of double images observed in these experiences is not "double vision." Double vision refers to the experi­ ence of seeing two objects where you are cen­ tralizing. There is supposed to be only one fused object at the point of centralization. At

least initially, double vision is frequently a consequence of strabismus, discussed more below.

To better understand fusion, and why there is a doubling of objects at other distances, refer to Figure 18-4: Near Finger Supplement.

appears to the V—• 1 •*—/ appears to the

\/left of the

right of the V

• / near finger.

near finger. \

For both eyes, ; /'; the near finger appears correctly •( 6; in the center

as one: V; fused finger.

The image of the far finger falls to the right of the fovea in the left eye (dashed line AB), while the image falls to the left of the fovea in the right eye (dashed line CD).

Since the images of the far finger fail on opposite sides of the foveas, there appear to be two far fingers—one to the right, and one to the left of the near finger.

Figure 18-4: Near Finger Supplement.

The attention is on, and both eyes are correctly converging to, the near finger. The center of the image of the near finger falls in the fovea of each eye. The finger is in the center of the picture for each eye. The brain merges the two fingers into one "fused" near finger.

By following the line of sight from the left eye out to the near finger and beyond, we can see how the far finger is located to the left of the near finger. The far finger is to the left of the center of the picture for the left eye, while the far finger's image falls to the right of the fovea; see dashed line AB.

By following the line of sight from the right eye out to the near finger and beyond, the far

finger is located to the right of the near finger. The far finger is to the right of the center of the picture, while the far finger's image falls to the left of the fovea; see dashed line CD,

Since the brain is seeing far fingers to both the right and left of the near finger (both to the left and to the right of the foveas), two far fingers are seen, not one. In the final analysis, the brain has no other option regarding the quantity and locations of the far finger.

CENTRALIZATION AND FUSION

When you notice a tree through your kitchen window, there are two ladybugs walking on the window, not one. If your attention goes to the ladybug, there are now two trees in the distance, not one.

Usually, the mind disregards the illusion of two images where we are not centralizing. The rods pick up the movements of objects not falling in the foveas. If a peripheral object is of interest or concern to us, the mind and eyes shift to centralize on the new object.

Also, the objects at other distances will be less clear than the object the eyes are centralizing and accommodating on.

When the pictures from both eyes are switched on in the brain, there are usually two images of objects in front of, and in back of, the object we are centralizing on. However, if the object we are interested in is more than twenty feet away, objects farther away usually do not appear to be double images.

The concepts of binocular vision and fusion help reinforce the importance of centralizing. The object of interest is meant to enter the fovea of each eye. In combination with the mechanism of accommodation, one can now appreciate that there is only one point

in all the universe where we have sharp, colorful, and fused vision—at the point of centralization.

^ E X P E R I E N C I N G H E A D B A L A N C E

Right Eye Lell Eye

Figure 18-5: Head Balancing.

Repeat the initial alignments in Part A, The

Far Finger (or Green Pencil), above.

Refer to Figure 18-5: Head Balancing, a, b, andc.

Keeping your attention on the far finger, move the (two) near fingers and the far finger downward until the tops of all fingers are at eye level. Notice the height of the two near fingers. Are the tops of the left and right near

Chapter Eighteen: Stereoscopic Vision

fingers at the same height, as in a? When the tops of the two near fingers are level, the head is balanced, at least from the right and left perspective.

Now, keeping the attention on the far finger, tilt your head very slightly to the left and then to the right. Be sure to only tilt your head, like the Leaning Tower of Pisa. Do not turn or rotate your head, or else the two near fingers may be lost. When you tilt your head to the left, the left near finger should move downward, and the right near finger should move upward, as in b. Conversely, when you tilt your head to the right, the right near finger should move downward, and the left near finger should move upward, as in c. (The doubled distant objects also move upward and downward.)

Optionally, an object far in the distance can be used instead of the far finger. With a very small head movement, sketch a far object while tilting your head. Again, notice the heights of the two near fingers.

If the two near fingers are not at the same height, tilt your head in the appropriate direction until they are at the same height.

This is a simple way of checking left/right head posture. Some people tilt the head to one side as a chronic habit—many without even knowing they do so. This is a strain on the neck, spinal column, and the visual system. Tilting the head to one side can lead to lack of normal fusion.

It is possible to experience the tops of the fingers being uneven, even though the head is level. This could be the case if a person has vertical strabismus. One eye may be looking up too high, while the other eye is looking straight ahead, normally, at the far finger. This is discussed more below.

Just for fun: Notice in a mirror that when

you tilt your head a small amount from left to right, the eyes rotate to retain their hori­ zontal alignment! This action is created by the oblique muscles.

T H E V I S I O N H A L O

Cut the excess wire so the vertical part is about eleven inches long. File the end smooth.

5.Side view of the Vision Halo.

6.Side view of Vision Halo on the head.

7.Front view of Vision Halo on the head.

For many students, the Vision Halo is an out­ standing teacher of centralization, movement, and head balance.

CREATING A VISION H A L O

Refer to Figure 18-6: The Vision Halo.

1. Obtain a piece of strong but flexible wire. Plastic-coated, solid aluminum fencing wire, available at or through many hardware stores, works great.

One and three-quarters loops from a 9"-diameter spool yields about 2Уг feet of wire. This is longer than the final length needed to form the halo, but the extra length at the end makes it easier to shape the last portion of the halo.

2.Unwind the first % part of the wire into a straight line as shown. Bend the last inch of the end of the wire (small arrow) outward a small amount so that the tip of the wire will not touch the head; file the end smooth.

3.Shape the circular part into an oval to fit around the head. Form a long, straight portion that points forward, away from the head. Make this part as straight as possible.

4.Bend the long forward part upward about 450 at the point shown. At ap­ proximately five inches out along this angled part, bend the remaining part straight downward at the point shown.

ALIGNIN G THE VISION H A L O

It is important to place the vertical bar exactly in front of the nose, and vertical. The window formed by the two vertical bars may seem to have a slight "V" shape. This is normal.

Do not look at the vertical bar for more than a moment—only long enough to align it properly.

Just as there were two near fingers when sketching Dixie Man in Part Q The Distant Dixie Man, above, you should now have "two" vertical bars, forming a "window" or "gate," when sketching distant objects.

LEARNIN G ABOUT VISION HABITS

WITH THE VISION H A L O

*Since the halo moves when the stu­ dent's head moves, there is a continuous biofeedback occurring. A locked head and neck makes the window freeze.

°If a student only moves the eyes to the left or right, the window will be lost— another reminder that the head is not moving.

*If the window is angled to the right or left, the student's head is tilting to the right or left, respectively.

*The tendency to want to see objects outside the window as clearly as objects inside the window is called diffusion. Vision is best within the window; this is called centralizing. This is especially

In the Fusion l activities presented above, some students do not see two fingers; they only see one. We want to have two fingers; this tells us both pictures are switched on in the brain.

If you correctly experience all of the Fusion l activities shown in Plate 53, you can skip ahead to Fusion 2—The Bead Game, below.

Refer to Plate 54: Amblyopia and Plate 53:

Fusion 1. The point of centralization is indicated by a small circle in all diagrams and images.

Compare Right Eye Amblyopia/Far Finger, d-i, to Fusion/Far Finger, a-2. In both of these images the attention is on the far finger. However, in d-i, the image for the right eye has "switched off." Only the image from the left eye is being processed by the brain, resulting in monocular vision. All objects— the near finger, the far finger, and Dixie Man—are one and solid. There are no doubled or semi-transparent images. The far finger is not a "fused" image since the right eye's image is not being combined in the brain with the left eye's image. The left eye sees the near finger to the right of the far finger, and Dixie Man is seen to the left of the far finger—the same positions as in a-2.

Left Eye Amblyopia/Far Finger, d-2, shows the picture seen when the left eye is amblyopic. Compare to d-i and a-2.

The other figures, e-i through/-2, show the pictures seen when viewing the near finger and Dixie Man, and when the right and left eyes are amblyopic.

It is fairly easy to understand all of the images in Plate 54: Amblyopia by repeating the activities in Fusion 1 and simply closing, or covering, one eye at a time. When you close one eye, you are simulating amblyopia. Then compare d-i and d-2 to a-2, e-i and e-2 to b-2, and/-i and/-2 to c-2.

"VARIATIONS ON AMBLYOPIA

Some students have one and a half fingers (or pencils). A "half" finger means that one of the two semi-transparent fingers (or Dixie Men) is more faint, or "ghostly," than the other semi-transparent finger. For example, when sketching the far finger, the right near finger may be seen relatively strongly, but the left near finger is very faint.

Or, there could be two strong near fingers at some times, and only one near finger at other times. These tell us one eye is switched on and the other is switching on and off.

Other variations include alternating amblyopia, where the picture from one eye turns off, and then the picture from the other eye turns off.

Amblyopia can be present only during certain activities.

Amblyopia can also be a function of the distance at which a person is centralizing. A student may have two near fingers while sketching the far finger, but only one far finger when sketching the near finger. Or, a student may have two fingers in the distance while sketching the near finger, but only one near finger while sketching the far finger.

As Bates mentioned above, there are many variations possible with amblyopia.

" L A Z Y E Y E " O R " T E N S E E Y E " ?

It is unfortunate the term "lazy eye" has been used to refer to amblyopia, for the amblyopic eye is not "lazy"; it is tense. (Another example of left-brain, "Puritan work ethic" language inappropriately applied to the primarily right-hemisphere, relaxed functions of the visual system.)

When people are told they have a "bad," "poor," or "lazy eye," the assumption is made

that the problem is occurring because the eyes are not working hard enough. In truth, the opposite is the case—there is too much strain on the visual system.

Bates said that many types of amblyopia are caused by strain.

Strabismic Amblyopia

Since a person with strabismus would likely experience double vision if both pictures stayed on, the brain most often turns one of them off. It is stressful to see two images everywhere, so the mind simply switches off one of the pictures. The mind usually turns off the eye that has strabismus. Again, there are many variations possible.

Other Types of Amblyopia

Amblyopia can also be caused by trauma, toxicity, nutritional deficiencies, ptosis (drooping of an eyelid), cataracts, corneal problems, macular degeneration, and other problems. Your eye doctor may be able to provide more information on these conditions.

ACTIVITIES FOR AMBLYOPIA

There are several activities a student can use to encourage the amblyopic eye to switch back on. Before doing these activities, the student may want to read the following section on convergence and strabismus. As mentioned above, amblyopia is often connected to problems of strabismus.

Refractive Amblyopia

Amblyopia is often found in people who have a large difference in acuity between the two eyes. This is called refractive amblyopia.

For example, if the brain is receiving a 20/40 image from one eye and a 20/400 image from the other, it would be difficult to merge these two images into one. In fact, to do so would likely result in a poorer image than the 20/40 image alone. By switching off the 20/400 image, the person can have "full" 20/40 with the other eye.

By using corrective lenses that bring the eye with 20/400 back up to 20/40, the amblyopic eye may be encouraged to switch back on.

Some students have nearsightedness in one eye, and farsightedness in the other. Oftentimes, the nearsighted eye is amblyopic when the attention is in the distance, and the farsighted eye is amblyopic when the attention is up close.

Part A: This activity is for amblyopes and students with a large difference in acuity between the two eyes.

1.Do the cross-crawl and/or the figure-8 pattern (up in the center) with the nose-pencil (or feather) for one or two minutes. This helps balance the right and left sides of the body and connects the right and left brains

2.Check for two fingers, both near and far, as described in "Fusion vs. Amblyopia," above. If there is only one finger where there should be two, or if you have a large difference in acuity between your two eyes, continue.

3.Cover (patch) the "switched-on" eye, or the eye that has better acuity.

4.Sketch a picture, nose-feather an object, toss a ball, do the Long Swing, or sun (with closed eyelids), etc., for three minutes. This activates the amblyopic or less clear eye and encourages it

to switch on and see simultaneously, or to see better, with the other eye.

5. Cover the "switched-off' eye, and do the same activity as in #4 above, for one minute. It is important to activate both eyes, not just one.

6. Remove the patch, and do the same activity as in #4 with both eyes for three minutes. This teaches the two eyes to see together equally.

7.If amblyopic, check for two fingers again. We want to have two, steady fin­ gers.

8.Palm for a few minutes.

If a student is nearsighted in one eye and farsighted in the other, do near-to-far swings with the nearsighted eye, spending more time sketching in the distance. Then do far-to-near swings with the farsighted eye, spending more time in the near area. Then do both eyes together near-to-far-to-near-to-far, etc.

The purpose of these activities is to "acti­ vate" and relax (not work) the eye with the greater strain. Effort should never be applied to any activities for improving vision. The three habits of natural vision, and the selfhealing activities such as palming and sun­ ning, bring relaxation to the visual system. Relaxation is the key to normal sight.

Part B: For amblyopes. (You may want to have someone assist you with this activity.)

1.Do the cross-crawl and/or the figure-8 pattern with the nose-pencil for one or two minutes.

2.Cover the "switched-on" eye.

3.Hold, or place, two pencils in front of you, vertically about four inches from your nose and about two inches away from each other horizontally. Now, posi-

tion one pencil in front of your nose, and the other slightly to the side of the uncovered eye. You should now have a two-pencil "window" through which the amblyopic eye is looking. Sketch a dis­ tant object through this window.

The purpose of this activity is to experi­ ence the two-pencil window and to place the picture of the distant object, located between the two pencils, into your mmd.This gives the brain an idea of what you want to see when holding only one pencil—without covering one eye.

4.Close both eyes, and remove the patch.

5.Keeping your eyes closed, remove the pencil in front of the amblyopic eye.

6.Pretend both eyes are open and you are seeing the distant object within the two-pencil window.

7.Being sure keep your attention on the object in the distance at all times, open both eyes and sketch the object in the distance. You may notice "two" pencils. The two pencils may appear only for a brief moment in the beginning. Also, they may not be equally strong. One may appear dim or "ghostly."

If you get the two-pencil window—even for a moment—congratulations! Both eyes were switched on at that moment! The eyes know how to see normally, and you have just given them the opportunity to improve!

If you did not get the window, continue to practice the above activities for amblyopia, and practice better vision habits each day. Palm and sun frequently.

This activity should be repeated until "two" pencils are seen consistently, while holding one pencil.