Fusional Vergence, Voluntary Convergence, and Antisuppression
Fusional Vergence Procedures: Anaglyphs, Polaroids, and Liquid Crystal Filters
VARIABLE VECTOGRAMS
Objectives
Increase the amplitude of negative fusional vergence (NFV) and positive fusional vergence (PFV).
Decrease the latency of the fusional vergence response.
Increase the velocity of the fusional vergence response.
Equipment Needed
Description and Setup
All variable vectogram slides come in pairs. The two slides are identical except for the polarization and disparity. These targets are designed to enable one to create convergence or divergence demand by separating them horizontally. Figure 6.1 illustrates the different vectograms. These procedures are performed with the Polaroid glasses that allow the right eye to see only one slide, while the left eye sees only the other slide. A convergence demand is achieved by moving the slide seen by the right eye to the left and the slide seen by the left eye to the
right. This forces the right eye to follow the target moving left and the left eye to follow the target moving right. If the target seen by the right eye is moved to the right, while the target seen by the left eye is moved to the left, divergence is stimulated.
right. This forces the right eye to follow the target moving left and the left eye to follow the target moving right. If the target seen by the right eye is moved to the right, while the target seen by the left eye is moved to the left, divergence is stimulated.
 ▪ Figure 6.1 Variable vectograms. |
Three newer vectograms are illustrated in Figures 6.2, 6.3, 6.4. The objectives, description and setup, procedures, important factors, and all other issues discussed relative to the vectograms apply to the variable tranaglyphs as well (Tables 6.1, 6.2, 6.3).
All vectogram targets have a scale at the bottom that indicates the amount of prismatic demand at any given target separation (Fig. 6.5). However, this scale is only correct if the patient is viewing the target at a distance of 40 cm. If the patient moves closer or farther away, the scale is no longer accurate. It is therefore important to understand how the vergence demand is calculated.
The basis for this understanding is the definition of a prism diopter. A prism diopter demand is defined as a separation of 1 cm at a distance of 1 m. To determine how this applies to any other given distance, the following formula can be used:
100 cm/1 cm = working distance/target separation in cm
If we want the working distance to be 40 cm, the formula is
100 cm/1 cm = 40 cm/x cm
100x = 40 cm
x = 0.4 cm, or 4 mm
Therefore, at 40 cm, a 4-mm target separation is equal to 1 Δ. To use this information clinically, the therapist would simply measure the distance between similar points on the tranaglyph and divide the distance in millimeters by 4 to determine the demand in prism diopters (each 4-mm separation equals 1 prism diopter of demand).
Similarly, if the working distance were shortened to 20 cm, a 2-mm separation would now equal 1 Δ. Thus, by decreasing the working distance, you increase the level of difficulty of the task for a given target separation.
 ▪ Figure 6.2 Vortex vectogram. |
 ▪ Figure 6.3 Baseball vectogram. |
 ▪ Figure 6.4 Gem vectogram. |
Table 6.1 RECOMMENDED PROCEDURES FOR ANAGLYPH AND POLAROID VISION THERAPY TECHNIQUES | ||||||||||||||
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Table 6.2 OTHER RECOMMENDED THERAPY PROCEDURES FOR BINOCULAR VISION THERAPY TECHNIQUES | ||||
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Table 6.3 PROCEDURES FOR INCREASING AND DECREASING VERGENCE DEMAND WITH BINOCULAR VISION THERAPY PROCEDURES | ||||||||||||||||||||
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 ▪ Figure 6.5 Scale at the bottom of a target indicating the prismatic demand at any given target separation. |
There are currently 12 vectograms available, 2 are fixed (only one slide) (Figs. 6.1, 6.2, 6.3, 6.4):
Fixed Vectogram
Figure Eight
Acuity Suppression
Variable Vectogram
Quoit
Clown
Spirangle
Mother Goose
Chicago Skyline
Stereo Test
Basic Fusion
Vortex
Baseball Spirangle
Gem
Although the 10 variable slides differ from one another in several ways, the primary differences are the size of the targets and whether the vectogram can be considered a central or peripheral target. When a stimulus is large and tends to have very little central detail (Quoit, illustrated in Fig. 6.1), it is referred to as a peripheral target.
This type of target primarily stimulates peripheral fusion. Stimuli like the Clown and Spirangle vectograms shown in Figure 6.1 are considered central targets because there is more central detail and the lines and detail are finer than the Quoit vectogram.
This type of target primarily stimulates peripheral fusion. Stimuli like the Clown and Spirangle vectograms shown in Figure 6.1 are considered central targets because there is more central detail and the lines and detail are finer than the Quoit vectogram.
Another difference in the vectograms is the size of the detail in each target, and therefore the degree of control of accommodation. A vectogram such as the Quoit (Fig. 6.1) has no fine detail, whereas the Clown and Spirangle have fine-line drawings. Depending on the stage and objectives of therapy, one type of vectogram may be more appropriate than another. For instance, early in therapy, it is often desirable not to use finely detailed central targets. Such targets require very precise accommodation on the part of the patient. In the early phases of therapy, it is easier for the patient to fuse if targets do not require precise accommodation. If a patient is being treated for a convergence insufficiency and has low PFV, it is best to initially permit the patient to use some accommodative convergence to help achieve fusion. If a target with fine accommodative detail is used, the patient will report blurred vision. Using a peripheral target without detail allows the patient to succeed initially. In later stages of vision therapy, it becomes important to use targets with as much fine detail as possible to ensure accurate accommodation.
The vectograms also have varying degrees of disparity. The Quoit vectogram shown in Figure 6.1 has no disparity at all, whereas the Clown and Spirangle vectograms (Fig. 6.1) have varying degrees of disparity from one area to another within the vectogram. All of the vectograms with disparity are designed to present nonuniform disparity from one part of the slide to another. For example, with the Baseball vectogram (Fig. 6.3) the letter “I” is seen ahead or closer to the patient than the letter “E” (more base-out).
Because vectograms allow one to vary the vergence demand, they are very useful early in therapy and are usually the first targets prescribed to expand the PFV and NFV systems. In the initial phase of therapy, it may be difficult for the patient to fuse in the direction of difficulty. For instance, with a convergence insufficiency patient, any convergence demand may be difficult at first. The advantage of the variable vectogram technique is that it allows you to begin therapy in the divergence direction and gradually reduce the divergence demand.
Therapy Procedures Using the Quoit Vectogram
Step 1 (Video 6.1)
The patient wears the Polaroid glasses, and the Quoit vectogram slides are set up in the dual Polachrome illuminated trainer. While the patient views the target, ask the patient what he or she sees. The patient should be able to describe the picture, which consists of a large Quoit, or rope-like object (Fig. 6.6). The patient should
state that there is a box on the lower left with “R” and “L” and that there are both vertical and horizontal lines (cross) on top of the Quoit (Fig. 6.6). If the patient does not voluntarily respond with these answers, ask leading questions to elicit this information.
state that there is a box on the lower left with “R” and “L” and that there are both vertical and horizontal lines (cross) on top of the Quoit (Fig. 6.6). If the patient does not voluntarily respond with these answers, ask leading questions to elicit this information.
 ▪ Figure 6.6 Quoit vectogram targets set at different prismatic demands in a Polachrome illuminated trainer. |
Step 2 (Video 6.2)
Tell the patient to concentrate on the large Quoit target. While the patient looks at the Quoit, slowly separate the two sheets to create a small amount of convergence demand and then a small amount of divergence demand. Ask the patient to try to keep the Quoit clear and single and describe what he or she is seeing. The patient should say that the target becomes smaller and closer when you create convergence demand and larger and farther away with divergence demand. This is the “small in, large out” (SILO) response described in Chapter 5. If the patient is unable to spontaneously describe this, it is important to ask leading questions to obtain these responses. Typical questions would be as follows:
Is the picture becoming larger or smaller?
Is the picture coming closer or moving farther away?
Once you can establish that the patient is experiencing either SILO or “small out, large in,” question him or her about diplopia, blur, float, localization, and parallax. Explain to the patient that these are all feedback cues that will be used throughout therapy to help monitor his or her responses.
Step 3 (Video 6.3)
Now set the sheets at zero and explain to the patient that you are going to demonstrate the procedure that he or she will practice. It involves three distinct parts:
1. Tell the patient to separate the sheets to number 3 base-out and try to keep the Quoit single and clear.
2. Instruct the patient to take the pointer and point to the location at which he or she sees the Quoit floating. Make sure the patient sees one pointer and one Quoit. Stress to the patient the importance of the kinesthetic awareness or feeling of “looking close” and “crossing his (or her) eyes.”
3. Now ask the patient to put the pointer down and look away from the Quoit to a point farther away for several seconds and then to regain fusion. Have the patient hold fusion for 10 seconds, look away, and look back again. Instruct the patient to repeat this three times.
Once the patient can perform these steps while the Quoits are set at 3 base-out, have the patient separate the targets three more numbers of base-out and repeat steps 1 to 3. At some level, the patient will be unable to successfully complete even step 1—seeing the Quoit clearly and singly. At this point, it is critical to teach the patient a method of overcoming this obstacle. To simply have the patient decrease the disparity until he or she can fuse again is not an effective therapy strategy. If the patient is experiencing diplopia, use the feedback technique of localization described in Chapter 5 to show him or her how to regain fusion (Video 6.4).
Step 4 (Video 6.5)
The same steps are followed for divergence therapy, except that the patient will be unable to physically point to the location at which he or she perceives the target. After 6 to 8 base-in, the apparent target location will be too far behind the targets for the patient to point. If the patient is experiencing difficulty, we suggest that you use the procedure for teaching divergence localization discussed in Chapter 5, using a Quoit vectogram and a Marsden ball.
Other Therapy Procedures That Can Be Performed with Vectograms
In Chapter 5, we described the differences between tonic and phasic therapy procedures. The vectogram techniques described to this point emphasize the tonic or sliding method. They are useful in the initial phase of therapy and are designed to improve the amplitude of the fusional vergence response. Once the patient can achieve a moderate level of convergence and divergence (20 to 25 base-out and 10 to 15 base-in), the vectograms can be used to create a step- or phasic-type demand to improve fusional facility (Table 6.2).
Phasic or Step Vergence Therapy
There are several ways to create a step vergence demand. These include the following:
1. Changing fixation from the target to another point in space Ask the patient to fuse the vectogram, then look away for several seconds, and look back and regain fusion.
2. Breaking fusion by covering one eye After the patient has fused the vectogram, have him or her cover one eye for 5 to 10 seconds to break fusion. The patient then uncovers his or her eye and has to regain fusion.
3. Using loose prism or flip prism or lenses (Video 6.6)
(a) While the patient is fusing the vectogram target at a particular convergence or divergence demand, additional prism can be placed in front of the patient’s eyes to create a large change in vergence demand.
(b) Flip lenses can also be used to create a step vergence change in vergence demand. If +2.00 lenses are placed in front of a patient fusing 20 base-out, an additional convergence demand is generated. The exact demand is based on the accommodative convergence/accommodation (AC/A) ratio for the particular patient. The larger the AC/A ratio, the larger the vergence demand. For example, if the patient has an 8:1 AC/A ratio, the +2.00 lenses will force the patient to relax 2 D of accommodation to regain clarity. As a result, he or she will relax 16 Δ of accommodative convergence. To maintain single binocular vision, the patient will therefore have to use 16 Δ of PFV. Alternatively, the patient may not fully relax accommodation, thereby decreasing the amount of PFV necessary to maintain binocular vision. If this occurs, he or she will report one blurred target.
Another way to understand the effect of lenses on vergence demand is to visualize the planes of accommodation and vergence for the vectogram task as described in Chapter 5. When plus lenses are added, the plane of accommodation moves away from the patient while the plane of vergence remains in the same location. The effect is an increase in the distance between the two planes and an increase in convergence demand.
4. Setting up two different targets in a dual Polachrome illuminated trainer (Fig. 6.6) (Video 6.7) The one on top can be set at one convergence demand and the one on the bottom at a different convergence demand. Ask the patient to fuse the top target, hold it for 10 seconds, and then change fixation to the bottom target and hold fixation for 10 seconds. This procedure can be repeated several times and then the demands changed.
5. Use Polaroid flippers that are designed to switch from which eye sees the right slide and left slide as the Polaroids are flipped (Video 6.8). When the patient views the target through one side, the demand is in the convergence direction. When the glasses are flipped to the other side, the same target creates a divergence demand. Polaroid filters in flippers can also be used in a similar fashion.
Binocular Accommodative Facility Therapy
Vectogram targets can be used for binocular accommodative facility (BAF) therapy. Select a vectogram that has finely detailed targets and, with the patient fusing at any vergence demand, use flip lenses to create a binocular accommodative demand. In this procedure, the patient must maintain vergence at the given demand and alter accommodation.
Vergence Therapy at Any Working Distance
Vectogram can be used for vergence therapy at almost any working distance. In almost all cases, therapy is initiated at near (40 cm) because it tends to be easier to train vergence ranges at near. In cases such as divergence excess, divergence insufficiency, basic esophoria, and basic exophoria, vergence therapy at distances greater than 40 cm is necessary. A patient can be moved several feet away from the vectogram target. It is important to remember that as the working distance is increased, the demand for a given separation decreases, the accommodative demand decreases, and the target becomes more central. Therefore, the targets must be separated to compensate for the change in working distance.
After about 1 m (3 ft), however, the targets are no longer effective because they become too small for the patient to resolve detail. To work at distances greater than 1 m, an overhead projector can be used. The vectogram is placed in a clear horizontal holder and placed on an overhead projector. The patient can stand as far away as necessary, and the same procedures described previously can be performed.
Important Factors
In working with vectograms, it is important to emphasize the following issues:
The kinesthetic feeling of converging and diverging.
The ability to clear the target and regain binocular vision as quickly as possible as the vergence demand is increased.
The patient, not the therapist, should manipulate the targets.
The glasses and targets are not doing anything; rather, the changes are internal, occurring within the patient’s own visual system.
The importance of maintaining clarity when fusing.
Changing the Level of Difficulty of the Task
The various methods of increasing and decreasing the level of difficulty of the task are summarized in Table 6.3.
Increasing and Decreasing the Level of Difficulty of the Task
Convergence
Minus lenses and base-in prism (BIM) decrease the level of difficulty by decreasing the separation between the planes of accommodation and vergence. BIM is an acronym used by clinicians to remember that base-in (BI) and minus lenses (M) have a similar effect on the level of difficulty of the task. Another way to decrease the demand is to increase the working distance. Recall that the prismatic demand created by any particular lateral separation of the targets is determined by the working distance. At a working distance of 40 cm, 4 mm equals 1 Δ. The same 4-mm separation is only 0.5 Δ at a distance of 80 cm.
Plus lenses, base-out prism (BOP) and decreasing the working distance increase the level of difficulty by increasing the separation between the planes of accommodation and vergence. BOP is an acronym used by clinicians to remember that base-out (BO) and plus lenses (P) have a similar effect on the level of difficulty of the task.
Divergence
BOP and increasing the working distance decrease the level of difficulty of the task, whereas BIM and decreasing the working distance increase the level of difficulty of the task.
Endpoint
To determine when to discontinue this therapy technique, it is important to consider the original diagnosis and the size of the heterophoria. A general guideline is to discontinue this procedure when the patient is able to
Achieve 20 to 25 base-out and 10 to 15 base-in.
Alternate from 20 to 25 base-out to 10-15 base-in
VARIABLE TRANAGLYPHS
Objectives
Increase the amplitude of NFV and PFV.
Decrease the latency of the fusional vergence response.
Increase the velocity of the fusional vergence response.
Equipment Needed (Figs. 6.7 and 6.8)
Bernell variable tranaglypha (Series 500 and 600)
Dual Polachrome illuminated trainera
Horizontal holdera
Red/green glassesa
Red/green flip lensesa
Pointer
510: Peripheral fusion
515: Peripheral fusion and stereopsis
520: Peripheral fusion and central target
601: Bunny
605: Spiral
606: Clown
607: Airport
610: Sport slide
The objectives and use of the variable tranaglyphsa are identical to those just discussed for variable vectograms. In fact, the only real difference between the two techniques is that one type of target is printed in Polaroid material (vectograms), whereas the other is red/green (tranaglyphs) (Fig. 6.9). Historically, variable vectograms preceded variable tranaglyphs by many years. The primary reason for the introduction of the tranaglyph targets was cost. One set of variable vectograms costs approximately 8 to 10 times more than one set of tranaglyph targets. The various targets available in the tranaglyph series closely match those available in the vectogram
series. Clinically, there is one important difference between the vectograms and the tranaglyphs. There have been reports of patients experiencing considerably more difficulty with tranaglyph-type targets. The use of red/green targets appears to create an obstacle to fusion, particularly for patients with moderate-to-severe suppression and with significant accommodative anomalies. A possible theoretical explanation for this difficulty has been suggested by Bogdanovich et al.1 They studied the properties of red/green anaglyphic materials and found that currently available glasses can induce significant inequalities in retinal illuminance. These inequalities may precipitate or exacerbate suppression tendencies. They also found problems with ghost images and lateral chromatic aberration that could affect binocular vision. The major disadvantage is that suppression is a more significant issue with tranaglyphs than with vectograms. Thus, it is highly recommended to use vectograms for office-based vision. The tranaglyphs become useful as a technique that can be sent home to reinforce office-based vision therapy once the patient’s binocular vision has improved enough to successfully use tranaglyphs.
series. Clinically, there is one important difference between the vectograms and the tranaglyphs. There have been reports of patients experiencing considerably more difficulty with tranaglyph-type targets. The use of red/green targets appears to create an obstacle to fusion, particularly for patients with moderate-to-severe suppression and with significant accommodative anomalies. A possible theoretical explanation for this difficulty has been suggested by Bogdanovich et al.1 They studied the properties of red/green anaglyphic materials and found that currently available glasses can induce significant inequalities in retinal illuminance. These inequalities may precipitate or exacerbate suppression tendencies. They also found problems with ghost images and lateral chromatic aberration that could affect binocular vision. The major disadvantage is that suppression is a more significant issue with tranaglyphs than with vectograms. Thus, it is highly recommended to use vectograms for office-based vision. The tranaglyphs become useful as a technique that can be sent home to reinforce office-based vision therapy once the patient’s binocular vision has improved enough to successfully use tranaglyphs.
 ▪ Figure 6.7 Quoit vectogram. |
 ▪ Figure 6.8 Peripheral variable tranaglyphs. |
 ▪ Figure 6.9 Central variable tranaglyphs. |
NONVARIABLE TRANAGLYPHS
Objectives
The objectives of nonvariable tranaglyphs are identical to those described for variable tranaglyphs.
Equipment Needed
Bernell nonvariable tranaglyphsa (Series 500)
Dual Polachrome illuminated trainer
Horizontal holder
Red/green glasses
Red/green flip lenses
Pointer
Description and Setup
The nonvariable tranaglyphs are a set of six plastic targets produced by Bernell (Fig. 6.10). The targets are red and green and are printed on a clear background. Unlike the 500 and 600 series, they are nonvariable. This means that each slide has a specific disparity. There is only one plastic slide per target, unlike the variable tranaglyphs, which have two slides for each target design. Thus, the disparity cannot be altered in the same manner as with the variable tranaglyphs. Rather, the demand is changed by having the patient switch fixation from one target to another on a particular slide. Another way to vary the demand is to use auxiliary lenses or prism or both.
To change the task from convergence to divergence, one simply switches the glasses from red over OD to red over OS. Alternatively, the slide can be turned around while the red lens remains over the right eye.
Unlike the variable tranaglyphs and the variable vectograms, all targets in this series present a fixed vergence demand and require an initial fusional vergence movement (jump or phasic vergence therapy) to obtain fusion. The variable tranaglyphs or vectograms, of course, can be set at ortho or zero initially, before the demand is increased. The nonvariable tranaglyphs are therefore considered a more difficult technique.
 ▪ Figure 6.10 Nonvariable tranaglyphs. |
Therapy Procedures with Nonvariable Tranaglyphs Series 50
Step 1
The patient wears the red/green glasses, and the tranaglyph targets are set up in the dual Polachrome illuminated trainer. While the patient views the target, ask the patient what he or she sees. The patient should be able to describe that he or she sees the various stimuli at different planes. Some of the targets are seen in front of the plane of the tranaglyph, whereas others are seen behind the plane. On each nonvariable tranaglyph card, the divergence and convergence demands are printed directly next to the targets. These prismatic demands are only accurate when the technique is performed at 40 cm. To determine the prismatic demand at any other distance, use the formula described previously.
Step 2
Tell the patient to concentrate on the upper left-hand target and try to achieve one clear image. Have him or her hold fusion for 10 seconds. Instruct the patient to take the pointer and point to the location at which he or she sees each of the targets floating. Make sure the patient sees one pointer and one set of targets each time he or she points. Stress to the patient the importance of the kinesthetic awareness or feeling of “looking close” and “crossing his (or her) eyes.”
Step 3
Now ask the patient to put the pointer down and look away from the target to a point farther away for several seconds and then to regain fusion. Have the patient hold fusion for 10 seconds, look away, and look back again. Instruct him or her to repeat this three times. If the patient is unable to fuse a particular target, it is important to use the localization technique described previously with the variable vectograms.
Have the patient switch fixation to the next target and try to fuse. He or she should continue changing fixation from one target to another for several minutes. Other therapy procedures that can be performed with nonvariable tranaglyphs, along with important factors to consider and methods of changing demand, are listed in Tables 6.2 and 6.3.
Endpoint
Discontinue this therapy technique when the patient is able to successfully achieve clear single binocular vision with all six slides in Series 500 for convergence and slides 1 to 4 for divergence.
COMPUTERIZED BINOCULAR VISION THERAPY PROCEDURES
Since the mid-1980s, computer software has been available for vision therapy. Programs are now available that contain techniques to train accommodation, fusional vergence, saccades, pursuits, and various visual perceptual functions. These techniques usually require the use of anaglyphic or liquid crystal glasses. Currently, there are
many computer-assisted software programs being used by optometrists for both home- and office-based vision therapy.
many computer-assisted software programs being used by optometrists for both home- and office-based vision therapy.
An important question is why we should even consider using computer programs for vision therapy. Many of the techniques described in this chapter are relatively inexpensive and have proven their effectiveness over many years. What are the advantages of computerization of vision therapy to warrant the much higher investment in hardware and software?
Cooper,2 Press,3 and Maino4 have reviewed this issue. They noted the following problems associated with traditional noncomputerized techniques:
Methods of changing stimulus parameters are slow and unreliable.
Traditional techniques often require an experienced doctor or technician to interpret patients’ responses and to use that information to alter stimulus conditions in order to improve binocular response.
With young children or with older patients who are not responding accurately for a variety of reasons, traditional techniques become difficult and unreliable to use. The child who “learns” the expected response and has a strong desire to please the therapist may “give the right response,” even though he or she is not achieving the desired objective.
For learning to occur, feedback should be accurate, immediate, consistent, and unbiased. With traditional therapy techniques, the feedback is often provided by the therapist. Vision therapy is often conducted with one therapist working with two or more patients at a time. The feedback may therefore not always be as consistent and immediate as desirable.
The advantage of computerized vision therapy is that it overcomes each of the problems listed.5,6,7 In addition, computer techniques allow for standardization of therapy techniques and thereby improve intra- and intertherapist reliability and, from our clinical experience, represent a valuable motivational tool. Both children and adults seem to enjoy and look forward to computer techniques compared with traditional procedures. There has also been some investigation that demonstrates the efficacy of computerized vision therapy for improving visual function.2,4,8,9,10,11,12,13
It is beyond the scope of this book to attempt to review every available computer-based vision therapy program. We advise readers to refer to the Bernell and Optometric Extension Program catalogs to try and be current with the release of new programs. However, we review a few of the more popular programs.
OFFICE-BASED COMPUTER VISION THERAPY SOFTWARE FOR BINOCULAR VISION
Computer Orthoptics VTS4 Liquid Crystal System
One software package that we have found to have significant value is the Computer Orthoptics VTS4 Liquid Crystal System.c It involves the use of liquid crystal filters and is, therefore, described in this section. This software package has a wide variety of procedures that are useful for office-based vision therapy for accommodative, vergence, and eye movement disorders. We do not attempt to present an exhaustive description of the software. Rather, we concentrate on the procedures using random dot stereograms. Programs are continually being revised and added, and anyone interested in vision therapy should be in contact with all of the companies listed at the end of the chapter (see Sources of Equipment).
Multiple Choice Vergence Program
Objectives
Increase the amplitude of NFV and PFV.
Decrease the latency of the fusional vergence response.
Increase the velocity of the fusional vergence response.
Equipment Needed
PC-compatible computer
50-in. large screen monitor
Computer Orthoptics VTS4 Liquid Crystal System software
Liquid crystal glasses
Description and Setup. This program uses high-speed liquid crystal glasses that result in complete cancellation of the targets. The circuitry developed for the high-speed liquid crystal glasses allows binocular stimuli to be alternately darkened 60 times per second (60 Hz). The glasses are matched to a color monitor that also
alternates left and right eye view at 60 Hz. This allows vivid color binocular targets to be presented to each eye with almost no ghosting. These glasses eliminate the problems associated with red/green and red/blue filters, such as poorer-quality fusion because of color rivalry, different accommodative demands from chromatic aberration, and chromostereopsis. The Computer Orthoptics VTS4 software is currently used with a 50-in. plasma screen television monitor and can also be used with a projector to create large peripheral targets and can be helpful in the initial stages of therapy or when working with a patient with a distance-related binocular vision disorder.
alternates left and right eye view at 60 Hz. This allows vivid color binocular targets to be presented to each eye with almost no ghosting. These glasses eliminate the problems associated with red/green and red/blue filters, such as poorer-quality fusion because of color rivalry, different accommodative demands from chromatic aberration, and chromostereopsis. The Computer Orthoptics VTS4 software is currently used with a 50-in. plasma screen television monitor and can also be used with a projector to create large peripheral targets and can be helpful in the initial stages of therapy or when working with a patient with a distance-related binocular vision disorder.
The random dot stereopsis feature of this software has several advantages that make it one of the more powerful binocular vision therapy procedures currently available:
It is one of the few available techniques that utilize random dot stereopsis targets.
The liquid crystal technology tends to minimize suppression.
The method of changing stimulus parameters is fast and reliable. The vergence demand is automatically increased 1 Δ if the patient responds correctly, and it is reduced by 2 Δ if the response is incorrect.
Because the stimulus is a random dot stereopsis target, the patient can only perform the task if he or she is fusing appropriately. The procedure is therefore objective and does not depend on the patient’s ability to communicate about what he or she is seeing and experiencing. This makes this technique valuable for younger, less verbal children. The therapist is better able to manage the child who “learns” the expected response on other techniques and has the desire to please the therapist.
Feedback is accurate, immediate, consistent, and unbiased.
A patient can work independently on the computer, freeing the therapist to work with another patient.
Scoring is automatically done by the computer.
The Multiple Choice Vergence program is a basic binocular vision therapy program that can be used at the very early phase of vision therapy. It is most comparable to the use of variable vectograms. The demand is initially set at zero and can be set in the vergence direction that is easiest for the patient.
The stimulus for this program is a large square with a smaller random dot stereopsis square embedded within it, located on the top, bottom, right, or left of the larger square. The patient is instructed to move a joystick in the direction in which he or she sees the small square. Five target sizes are available (extra large, large, medium, small, and extra small).
The technique is designed for use at 40 cm. The vergence demand indicated by the computer is based on the premise that the patient is sitting at a distance of 40 cm from the screen. If the working distance is shorter or longer, you must adjust these numbers based on the formulas reviewed on page 152.
Therapy Procedures. Have the patient sit 40 cm from the screen, wearing the red/blue glasses. Select the Random Dot program from the submenu for vergence. We recommend that the length of the therapy setting be changed to 3 minutes. All other parameters can be left at the default setting. Select base-in or base vergence based on the patient’s diagnosis. Instruct the patient that he or she is to determine where the small square is located and to move the joystick to this location. If the small square is on top, he or she moves the joystick forward; if it is on the right, he or she moves the joystick to the right, and so forth (Fig. 6.11).
The key to this program is that if the patient is not able to fuse, there is no way for him or her to succeed at this task or to make the therapist think that he or she is succeeding. With most vision therapy techniques, it is rather easy for a patient to learn the expected responses. Children trying to please the therapist may give this expected response even if they cannot actually succeed at the task.
Other Therapy Procedures That Can Be Performed with Computer Orthoptics Software. Once the patient has been able to reach 40 to 50 base-out and about 10 to 15 base-in, select the program that emphasizes vergence facility and presents a phasic or jump vergence-type demand, called Step-Jump Vergence. This program automatically switches from a convergence to a divergence demand in a stepwise fashion. For example, you may begin at 10 base-out and 5 base-in. After the patient correctly responds to 10 base-out, the computer switches to 5 base-in and then to 11 base-out, 6 base-in, 12 base-out, 7 base-in, and so forth. When the patient can successfully reach 40 base-out and 16 base-in, you can select the Jump-Jump Vergence program. This program presents an alternating demand between convergence and divergence in a random (rather than stepwise) manner. Several variations in technique can be prescribed to vary the activity and increase the level of difficulty. These include the same techniques described in detail for other binocular vision therapy techniques.
Important Factors. When performing this procedure, it is important to emphasize the issues listed in Table 6.4.
Changing the Level of Difficulty of the Task. The various methods of increasing and decreasing the level of difficulty of the task are summarized in Table 6.3.
Endpoint. Discontinue this therapy technique when the patient is able to achieve clear single binocular vision with 40 to 50 base-out and 10 to 15 base-in.
 ▪ Figure 6.11 A: Child working with the Computer Orthoptics Random Dot Stereopsis program. B: Patient’s view of the Computer Orthoptics Random Dot Stereopsis target. |
Table 6.4 IMPORTANT FACTORS TO EMPHASIZE DURING BINOCULAR VISION THERAPY PROCEDURES | |||||
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Computer Aided Vision Therapy: Computer Vergences Program
Another effective software package is Computer Aided Vision Therapy (CAVT). The Computer Vergences program from this software package can be used to work with vergence problems. In contrast to the Computer Orthoptics program, this program requires the use of red/blue filters. The Computer Vergences software program offers a selection of 10 procedures. The one we find most useful is Random Dot Stereograms. It is particularly effective because of its use of random dot stereopsis stimuli, whose advantages were described previously.
CAVT Random Dot Stereograms: Jump Vergences
