Introduction and General Concepts
This chapter provides detailed information and guidelines for vision therapy, and Chapters 6, 7, 8 describe a select group of vision therapy procedures for the treatment of vergence, accommodative, and ocular motility disorders. There are hundreds of vision therapy techniques in use by optometrists, and manuals describing a wide variety of instrumentation and procedures are available.1,2 In our opinion, presentation of a vast array of procedures tends to make vision therapy appear overly complicated. We believe that this may discourage optometrists from becoming involved in vision therapy.
In Chapters 6, 7, 8, we present a select group of procedures and instruments. Our primary emphasis is on presentation of the principles underlying the vision therapy techniques we have selected. An understanding of this small group of vision therapy procedures will enable an optometrist to successfully treat the vast majority of accommodative, ocular motility, and nonstrabismic binocular vision disorders and achieve success rates consistent with those discussed in the literature.3,4,5,6,7,8,9,10,11,12 In addition, the principles discussed for these vision therapy techniques are common to all procedures. Therefore, an appreciation of the key issues and principles in this chapter will allow the clinician to understand almost any other procedure and will permit growth as the practitioner gains experience and confidence.
It is not unusual for us to hear students and clinicians unfamiliar with vision therapy ask the question, “What do I do with it?” regarding vision therapy equipment. Therefore, one of the primary objectives of the following four chapters is to provide a detailed description of how to actually use the vision therapy equipment described. We have provided a detailed sequence of therapy procedures to perform with the specific instruments described. We are well aware that there are other ways to use this instrumentation, but our goal is to present a starting point for clinicians, who then can expand their utilization of this equipment as they gain experience in the area of vision therapy.
Categorization of Vision Therapy Instrumentation and Procedures
Binocular vision therapy procedures have traditionally been subdivided into two broad categories. The first category, referred to as instrument training, includes all techniques in which the patient is required to look directly into an instrument. With instrument training, movement of the patient is restricted, and it may be difficult to see the patient’s eyes. These conditions are generally described as being less natural or more artificial than other forms of therapy. The most common example of instrument training is the use of a stereoscopic-type device.
The second category, called free space training, involves techniques in which the patient is in a less restricted environment, more movement is possible, and it is easier to observe the patient’s eyes. This type of vision therapy more closely approximates normal seeing conditions and is considered less artificial than instrument training.
Upon careful analysis of this division, several problems become apparent. The first difficulty is the lack of precise criteria for placing a particular procedure in either category. For example, although the Aperture Rule, illustrated in Figure 5.1, is generally considered a free space technique, a patient using this device clearly has to position himself or herself directly against the device and look into the instrument. The same is true of the double mirror stereoscope shown in Figure 5.2. Although these two devices do not use lenses or prisms, they clearly resemble “instrument” devices such as the stereoscope shown in Figure 5.3. Another problem is how to categorize anaglyphic and Polaroid filter procedures. Are these techniques truly “free space,” or do the filters constitute an interference and alteration in the normal visual environment?
We believe that the “free space” versus “instrument” dichotomy is an artificial division that leaves too many devices and procedures without a clear fit into either category. We recommend a classification of vision therapy instrumentation and techniques that is based to a greater extent on the type of equipment being used. This classification is as follows:
 ▪ Figure 5.1 The Aperture Rule. |
 ▪ Figure 5.2 Double mirror stereoscope. |
 ▪ Figure 5.3 Bernell-O-Scope stereoscope. |
1. Anaglyphs and Polaroid filters
2. Lenses, prisms, and mirrors
3. Septa and apertures
4. Paper, pencil, and miscellaneous tasks
5. Stereoscopes
6. Afterimages, entoptic phenomena, and electrophysiologic techniques.
This classification system is used throughout Chapters 6, 7, 8 as common vision therapy techniques are described. Table 5.1 lists many of the various instruments and procedures that fall into these six different categories.
Table 5.1 CLASSIFICATION OF VISION THERAPY INSTRUMENTATION AND PROCEDURES | ||||||
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The concept of natural versus artificial training conditions, however, is a useful one that we emphasize throughout this text. There is a general consensus that vision therapy procedures that approximate normal seeing conditions tend to be more effective in achieving the desired objectives of vision therapy.
CATEGORY 1: ANAGLYPHS AND POLAROID FILTERS
Anaglyphs and Polaroids are filters that block out light from a portion of the target being viewed so that one part is visible by one eye and one part is visible by the other eye. These techniques are widely used for heterophoria patients.
Advantages
Anaglyphs (red/green targets) and Polaroids allow good control of stimulus parameters. A wide variety of targets, including second-degree, third-degree, central, peripheral, accommodative, and nonaccommodative targets, are
available. These techniques work well with shallow to moderate suppression, and can be used to train both jump (phasic) or smooth (tonic) vergence. Because the patient does not have to look into an instrument, these procedures more closely resemble normal seeing conditions than instrument-type devices.
available. These techniques work well with shallow to moderate suppression, and can be used to train both jump (phasic) or smooth (tonic) vergence. Because the patient does not have to look into an instrument, these procedures more closely resemble normal seeing conditions than instrument-type devices.
Disadvantages
Young children may lose interest, and it is important to use a variety of targets to maintain interest. The primary disadvantage of Polaroid techniques is high expense. They are approximately 10 times as expensive as anaglyphs. Another problem associated with Polaroids is that if the patient tilts his or her head, both targets can be seen by one eye. This would allow the patient to see both targets even if he or she is suppressing. Although anaglyphs are less expensive, these filters (particularly the red) are darker than Polaroids and may precipitate suppression.1 A potential disadvantage associated with both anaglyphs and Polaroids is that if there is rapid alternate suppression, it may be difficult to determine whether suppression is present.
CATEGORY 2: LENSES, PRISMS, AND MIRRORS
Lenses change the accommodative and vergence demand, whereas prisms and mirrors change the direction of light. Lenses, prisms, and mirrors are often used in conjunction with anaglyphs and Polaroids and are among the most widely used procedures for heterophoria patients. These procedures are useful for antisuppression training and fusional vergence, as well as accommodative and ocular motility therapy.
Advantages
Lenses are very effective for accommodative therapy. These devices also allow the clinician to increase or decrease the level of demand of all binocular and accommodative techniques. They can be used to train both smooth (tonic) and jump (phasic) vergence.
Disadvantages
Young children may lose interest, and it is important to use a variety of targets to maintain interest.
CATEGORY 3: SEPTA AND APERTURES
A septum is a dividing wall that separates the view of each eye in normal space so that one eye sees one portion of a target whereas the other eye sees another. An example is the Remy separator (Fig. 5.4). An aperture is an opening or window that separates the views of each eye so that one eye sees one portion of the target whereas the other sees another part. The Aperture Rule (Fig. 5.1) is a popular vision therapy technique based on the use of an aperture.
 ▪ Figure 5.4 Remy separator. |
Advantages
A moderate variety of targets is available, and more targets can be made by the clinician. Apertures and septa work well to treat patients with shallow to moderate suppression.
Disadvantages
It is sometimes difficult to keep a young child’s interest with these techniques. Head position is also important with apertures and septa, and the child must sit still and maintain the prescribed head position. The demand of the target cannot be set at zero, forcing the patient to make an initial fusional vergence movement. Because of this, apertures and septa are generally used after anaglyphs, Polaroids, and lenses, prisms, and mirrors.
CATEGORY 4: PAPER, PENCIL, AND MISCELLANEOUS TASKS
This category includes training techniques that are printed on paper and designed to train vergence, accommodation, and accurate eye movements. Many of the eye movement tasks are also useful for suppression training when combined with anaglyphs. Another type of technique included in this category is the Brock string (Fig. 5.5), which is a string with beads that is used to take advantage of physiologic diplopia.
Advantages
These techniques are generally the least expensive therapy procedures. A sufficient variety of targets are available, and the techniques work well with shallow to moderate suppression. These techniques work especially well for convergence therapy.
Disadvantages
It is difficult to maintain interest in young children.
CATEGORY 5: STEREOSCOPES
Stereoscopes are designed on the principle of dividing physical space into two separate areas of visual space, each of which is visible to only one eye. This is accomplished by dissociating the eyes mechanically with a septum (Brewster stereoscopes, Fig. 5.3) or by using two separate viewing tubes or mirrors (Wheatstone stereoscopes, Fig. 5.2). In addition, stereoscopes use lenses and prisms (Brewster stereoscopes) or mirrors (Wheatstone stereoscopes) to allow one to test and train at different simulated distances. In most cases, vision therapy for heterophoric patients can be successfully completed without the use of stereoscopes. Instrument training is useful, however, under the following circumstances:
If a patient is experiencing difficulty fusing with techniques from other categories. Some patients respond better initially to instrument training techniques that present stimuli under less natural seeing conditions. Although this is unusual and not totally predictable, it is worthwhile to try stereoscopic procedures when a patient is not responding well to free space techniques.
After a patient has successfully completed the nonstereoscopic techniques described in Chapters 6, 7, 8 that are more natural. It is often useful to perform some training with stereoscopes at this point, because such training allows considerable flexibility with the type of target used and the distance at which therapy can occur. With conditions such as divergence excess, the most difficult task is a first-degree target at a distance setting. Stereoscopes are well designed to deliver this type of stimulus.
To provide variety, which is an important consideration in vision therapy. The use of stereoscopes is another way to improve fusional ranges and facility. A particularly useful technique, only available with
stereoscopes, is called tromboning. Tromboning can be performed with Brewster-type stereoscopes and is a procedure in which a target is moved toward and then away from the patient. The unique aspect of this technique is that as the target is moved toward the patient, he or she must accommodate to maintain clarity and diverge to maintain fusion. As a target is moved away, the patient must relax accommodation and converge. This, of course, is opposite to what occurs in the normal seeing environment and this is why this procedure is valuable.
 ▪ Figure 5.5 Brock string. |
Advantages
The primary strengths of this approach for nonstrabismic binocular anomalies are the ability to present a large variety of targets at distance and intermediate settings and the ability to select first-, second-, and third-degree targets. Stereoscopes can be effective even in cases of deep suppression.
Disadvantages
The artificial nature of the tasks involved in instrument training is a disadvantage of this approach. Questions have been raised about the transfer of improvements in binocular vision from the instrument to situations outside the instrument.1
Stereoscopes are the most expensive vision therapy techniques, and they can be heavy and bulky. As a result, many varieties are more appropriate for in-office therapy than home therapy.
CATEGORY 6: AFTERIMAGES, ENTOPTIC PHENOMENA, AND ELECTROPHYSIOLOGIC TECHNIQUES
Techniques in this category are used in the treatment of amblyopia, eccentric fixation, anomalous correspondence, constant strabismus, and nystagmus. Because these topics fall outside the scope of this text, we do not describe the majority of these procedures. Examples of therapy techniques included in this category are devices for creating afterimages, the Maxwell spot, the Haidinger brush, and auditory biofeedback. Afterimages are used occasionally in the treatment of ocular motor dysfunction, and we describe these procedures.
General Principles and Guidelines for Vision Therapy
Before describing the various categories of vision therapy procedures, it is important to understand that there are general principles and guidelines that apply to all vision therapy techniques, as well as specific principles and guidelines for binocular vision, ocular motility, and accommodative techniques. Vision therapy is similar in many ways to other types of therapy that involve learning and education. If we look at other types of learning, it becomes clear that there are specific guidelines to facilitate learning and success. Because vision therapy can be considered a form of learning and education, similar principles and guidelines must be used to achieve success. The following guidelines have been derived from basic learning theory.
Before beginning vision therapy, follow sequential management considerations (Chapter 3). When developing the vision therapy program, always consider amblyopia and suppression therapy before beginning fusional vergence therapy.
Determine a level at which the patient can perform easily. Working on this level makes it easier for the patient to become aware of the important feedback cues, strategies, and objectives involved in vision therapy, and also builds confidence and motivation.
Be aware of frustration level. Signs of frustration include general nervous and muscular tension, hesitant performance, and possibly a desire to avoid the task.
Use positive reinforcement. The patient should be rewarded for attempting a task, even if it is not successfully completed. Reinforcers can be verbal praise, tokens that can be exchanged for prizes, or participation in a task that the patient enjoys. Feldman13 has described, in detail, the various principles of behavior modification applied to optometric vision therapy. It is a valuable reference for clinicians involved with vision therapy.
Maintain an effective training level. Start at an initial level at which the task is easy and gradually increase the level of difficulty, being very careful to watch for signs of frustration. Vision training should be success oriented, that is, build on what the patient can do successfully, as opposed to giving tasks that are too difficult.
Emphasize to the patient that changes must occur within his or her own visual system. Birnbaum,14 in defining some of the critical concepts of which the vision therapist must be aware, goes beyond what should be done and concentrates on how vision therapy should be performed and the role of the vision therapist.
This role, according to Birnbaum, is to carefully arrange conditions for learning to occur. His view parallels ours, stressing the use of learning theory principles. More important, and perhaps the key to vision therapy, is teaching the patient to internalize changes in visual function, as opposed to just achieving certain criteria for specific techniques. Often, as patients go through a vision therapy program, they gain the impression that it is the instrumentation, lenses, or prism that effect the change in their visual system. Unless told otherwise, a patient may believe that these external items are the keys to their success in vision therapy.
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