The Shape of the Sky: The Introduction Art of Using Egocentric The digital age promises a quantum leap in the nonsurgical treatment of strabismus. Stereopsis in the Treatment New computerized vision therapy of Strabismus technologies, 3D movies, and the soon-to- explode field of virtual reality all promise David L. Cook, OD, FCOVD, FAAO advances in the presentation of stereoscopic Private Practice, Marietta, Georgia dichoptic displays technically impossible for most of the history of strabismus therapy. Abstract In a stereoscopic dichoptic display, we A protocol for using stereopsis in the present each eye with a target that is unseen treatment of strabismus is described. by the other eye. The two targets are slightly Suitable for patients with either normal different just as the views from two eyes in

ARTICLE retinal correspondence (NRC) or the natural environment are slightly different. anomalous binocular correspondence Sensory fusion allows the binocular illusion (ABC), the approach emphasizes the that dichoptic targets in physically different interactions between peripheral/egocentric positions are unified, creating the perception and central/relative stereopsis in such dichoptic of depth and often encouraging the alignment instrumentation as vectograms, digital of deviated eyes. instrumentation, and 3D movies. The paper Clinicians have long used such displays in the then discusses the transfer of appreciation treatment of strabismus. By the beginning of the of stereopsis from such artificial dichoptic twentieth century, Javal1 in France and Worth2 in stereoscopic presentations to consciousness England were already using mirror stereoscopes of egocentric and relative stereopsis in natural and major amblyoscopes (modified mirror seeing, emphasizing the art, rather than the stereoscopes) to produce dichoptic displays. science, of treatment. These instruments, however, created a number of challenges: Correspondence regarding this article should be 1. A limited field of view excluded the emailed to David L. Cook, OD, FCOVD, FAAO, at peripheral fusion that is largely responsible [email protected]. All state­ments are the author’s for maintaining alignment. As Brock,3 a personal opinion and may not reflect the opinions of the College of Optometrists in Vision Development, half a century later would write, “aversion Vision Development & Rehabilitation­ or any institu­ to fusion seems to be limited mainly to tion or organization to which the authors may be affiliated. Permission to use reprints of this article must the macular and paramacular region. For be obtained from the editor. Copyright 2016 College of this reason fusion training should begin Optometrists in Vision Development. VDR is indexed in with the periphery and only gradually the Directory of Open Access Journals. Online access is available at www.covd.org. https://doi.org/10.31707/ include the center.” The dichoptic targets VDR2016.2.4.p211 of stereoscopes and major amblyoscopes

Cook DL. The shape of the sky: the art of using ego­ were just too central. centric stereopsis in the treatment of strabismus. 2. In approaching the sensory system, the Vision Dev & Rehab 2016;2(4):211-37. motor system was often ignored, the eyes being allowed to remain in their strabismic Keywords: 3D movie vision therapy, posture while the illusion of sensory anomalous binocular correspondence, fusion occurred, combining targets that dichoptic therapy, egocentric stereopsis, physically had nothing to do with one optometric vision therapy, sphere of another. attention, stereopsis, strabismus

211 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 3. For those adapted so that eye position that will revolutionize nonsurgical treatment allowed an accurate perception of the of strabismus. This paper—based on my8 world free from the binocular illusions of forty years of experience in treating strabismic diplopia and confusion, the true perception patients, years including the transition into the of the instrument’s physically separated digital age—provides one strategy for how that apertures was often more perceptually revolution could occur. compelling than the illusions of blending and depth created by dichoptic targets. Depth Perception As Brock4 wrote, “the squinter … is apt to While allowing increased acuity, a spare eye, resent the fact that he no longer can see and an expanded field of view, the principal things as they really are and as he knows advantage of binocularity is enhanced depth them to be.” Similarly, Flax5 commented perception, particularly the appreciation of that strabismics “have learned to utilize stereopsis. There is little doubt on the importance those aspects of the incoming eye signal of stereopsis. Levi, Knill, and Bavelier9 have that are consistent with their logic and summarized the literature on how “stereopsis with their language constructs.” matters” in the areas of driving, visually-guided 4. Binocular illusions learned in an hand movements, motor control, walking, visual instrument that divorced the dichoptic feedback in control of movements, everyday images from interactions with hands and activities and adaptations to changes in terrain. body often did not transfer to natural If we divide space into three coordinates or seeing. Aware of such challenges, Brock,6 dimensions, x-axis or width, y-axis or height, and by the middle of the twentieth century, z-axis or depth, then depth perception is the had developed the use of free-space ability to determine the position of objects on anaglyphic stereoscopic displays. His the z- axis in free space … or to imagine a z-axis stereo motivator7, as it came to be called, in photographic images or realistic art. Depth projected stereoscopic images, which perception can include accurate objective allowed the direct comparison of dichoptic behavior in quantifying of space. It can also display illusions to real objects in a room include the subjective qualitative experience and allowed fusion confirmed by balance itself. In an attempt to distinguish the quantitative and movement. The lessons that Brock and qualitative aspects of depth perception, taught can now be advanced by digital Vishwanath has provided the following attempt technologies. Just as the increased safety at clarification: of anesthesia and fellowship programs I define “visual perception of depth or for the training of surgeons eclipsed 3-D structure” to generically refer to the nonsurgical strabismus treatment in the perception of the third dimension, in middle of the twentieth century, so will the pictures or real scenes, with one eye or advent of digital technologies restore the two, regardless of the cues inducing it or contributions of nonsurgical strabismus the qualitative impression associated with treatment in the twenty-first century. it. This includes the perception of both depth order and quantitative depth (e.g., Today’s digital instrumentation and blending the perception of 3-D shapes and locations of monocular and binocular cues in 3D movies of objects in a 3-D pictorial space). provide a welcome expansion of Brock’s “Stereoscopic vision” I take to literally innovations. It is not the digital dichoptic tools mean “vision through a stereoscope” or, by themselves, however, but the knowledge less literally, to refer to “binocular depth of their use as a springboard to natural seeing perception”: the visual perception of depth

212 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 on the basis of binocular disparities. I reserve When viewed through a monocular aperture, for the term “stereopsis” for the following: instance, photographs with good perspective The characteristically vivid impression of may become so three-dimensionally vivid that tangible solid form, immersive negative they approach the Greek stereos, meaning space and realness … that obtains under “solid,” from which our term stereopsis is certain viewing and stimulus conditions.10 derived. To capture this vividness, Vishwanath14 uses the term “monocular stereopsis” for the Like Vishwanath we will use “depth perception. In this paper, however, to avoid perception” in his first sense to include all z-axis confusion we will reserve the term stereopsis appreciation, including that in pictures. We will, for binocular perception. however, more traditionally, use “stereopsis” While the Verhoeff Stereopter and Howard to include both correct binocular localization Dolman Test both test depth perception of either natural or “dichoptic images,” naturally, the Titmus Stereo Fly and Wirt tests emphasizing the subjective qualitative “vivid are both examples of artificial stereopsis. The impression of tangible solid form and immersive Fly and Wirt test are both physically flat. Any negative space and realness” or what Barry has depth is, again, an illusion occurring only in the called “a palpable volume of empty space”11 If mind, not the apparatus, illusion being what the truth of treatment emerges from the sum of often occurs when we transfer how we “do” the perspectives, then additional perspectives vision in a familiar environment to how we “do” on the division of depth perception may provide vision in a novel or artificial environment. insights for understanding our treatment All dichoptic presentations, 3D movies approach. included, are examples of stereoscopic illu­ sions, not natural stereopsis. The perception of Monocular Versus Binocular Cues images springing off the movie screen is not to Depth perception is most commonly divided be found in the physical movie theater but in into depth from monocular cues versusdepth the minds of the viewers wearing the polarized from binocular cues. After Adler,12 monocular glasses. As will be described below under cues include interposition of one object in “Natural Stereopsis,” care must taken to ensure front of another, customary size of objects, that dichoptic illusions, once appreciated color and haziness of objects, convergence by those with strabismus, are transferred to of lines to the vanishing point, shadows, and appreciation of stereopsis in natural seeing. monocular parallax. To this list, we will add “looming,” which, like motion parallax, also Central/Relative Versus Peripheral/ requires comparison across time, not just Egocentric Depth Perception across space.13 Binocular cues, again according Burian15 provides a third highly profitable way to Adler, include convergence, binocular to divide localization of depth: relative versus accommodation, and stereopsis. egocentric. Suppose, for instance, a woman raises two fingers at arm’s length before her Artificial Versus Natural Depth Perception face and compares the fingers’ z-axis position Another way to divide binocular depth in space. If attention is constricted to the two perception is between artificial and natural targets, this is an example of relative depth perception of depth. Photographs, realistic perception (RDP). Both the Verhoeff Stereopter paintings, and 2D movies are all examples of and the Wirt test, for example, quantify RDP as artificial depth. The mind creates the illusion the viewer tries to determine the relative position of depth where none exists, transferring flat of targets. If however, in the two-finger example, images into three dimensional perceptions. the viewer instead considers the distance of the

213 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 two fingers from her face and is aware of the If a patient’s interpupilary distance (PD) is space in between her nose and both targets, six centimeters and the base out disparity of egocentric depth perception (EDP) is being the target is six centimeters, the eyes will be appreciated. During this heightened awareness converged to (and the fused image of the of EDP—in my experience as a viewer and target should be localized) half way between clinician—RDP often improves. As Vishwanath16 the patient and the physical location of the has hypothesized, “stereopsis is a qualitative disparated target. If the patient’s PD is six visual experience related to the perception centimeters and the target disparity is three of egocentric spatial scale. Specifically, the centimeters the target should be perceived to primary phenomenal characteristic of stereopsis float one fourth of the distance out between (the impression of “real” separation in depth) target and patient. If, for the same patient, is proposed to be linked to the precision with the target disparity is twice the PD the patient which egocentrically scaled depth (absolute should perceive the target to float outward depth) is derived.” Whether or not Vishwanath’s three fourths of the way from the target’s actual hypothesis is true, the key to improving position and the patient’s face. stereopsis in the therapy room and in real space For the purposes of therapy, I imagine that is very much linked to attention to EDP. egocentric localization and SILO are closely In the therapy room, the closest clinicians related to the area of space the viewer selects come to quantifying EDP is, perhaps, SILO for viewing. If, for instance in the above finger (Smaller In and Larger Out), the perception example, the viewer selects only the two in which dichoptic targets appear smaller fingers to view, there will be awareness of only and closer with base out disparity causing central or relative stereopsis. If, however, the convergence and larger and farther away with viewer selects all the space between his eyes base in disparity causing divergence. While and the two fingers then both central RDP and only stereoscopic or third degree dichoptic peripheral EDP will be perceived. targets offer RDP, simultaneous perception “Opening appreciation of space” to allow targets (first degree fusion), flat fusion targets for peripheral EDP/egocentric awareness of (second degree targets) and stereoscopic (third depth can be accomplished in some cases by degree fusion) targets all may be perceived to coaching to patient to be aware of the distance float in space using EDP. When perception of (volume of air or space, not an introverted spatial context is included, all targets may take estimate of feet or inches) between her nose advantage of EDP! and the target. Other viewers are more likely Measuring the accuracy of EDP is estimated to open up appreciation of space if coached by comparing the position of the two eyes and to “try to see everything in the room at once,” the actual location of each eye’s respective or if coached to be “simultaneously aware of target (Figure 1). the right and left walls at the same time” or “be aware of the length of the floor and ceiling at the same time.” The words “be peripheral” can be used, but only if the patient understands that “being peripheral” includes awareness of space, not just on the x-axis, but on all three axes: x, y, and z. The following proposed treatment approach will provide examples of this principle.

214 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 Treatment information will now be confirmed by both In our approach to using stereoscopic vision bifoveal superimposition and hand information. in the treatment of strabismus, two general All three will now support perceptual fusion of rules apply: 1) work with the eyes aligned the target. or approximately aligned and 2) encourage Precise stereoscopic vision depends on peripheral awareness. precise ocular alignment and gross peripheral stereoscopic vision depends on at least Alignment approximate alignment. In the words of Brock in “Anomalous binocular correspondence his lecture notes, “It is the nature of the posture (ABC) is diagnosed when the two eyes’ which determines the nature of the responses foveal images are perceived in different visual … while the eyes are in strabismic posture, the directions.”17 Unless the habitual angle of individual thinks strabismically, but the minute his deviation is disturbed, the patient typically eyes are in a normal posture he ceases to think perceives the objects related to foveal images strabismically and thinks the way we do.”20 Thus in their correct position in space, as if the patient whether or not a patient has ABC, stereoscopic knew where the eyes were pointing.18 The vision is likely to be appreciated when the eyes perception is in agreement with what the body, are voluntarily aligned or at least approximately including the hands, would confirm to be true. aligned to allow a peripheral fusion lock. Normal If the right eye is looking straight ahead at a retinal correspondence (NRC) versus ABC need monitor, and the left eye is turned toward a copy be considered when the eyes are deviated but of War and Peace on the bookshelf to the left not when the eyes are aligned and stereoscopic of the monitor, the exotropic patient with ABC vision is present. Even when the eyes are only will use the right eye to perceive the monitor approximately aligned so that a slip of eight straight ahead, which could be confirmed by or less prism diopters are observed on a touch. The left eye will simultaneously see unilateral cover test, the clinician concentrates War and Peace in its veridical (true) location not on reducing the degree of the slip but on to the left, again confirmable by touch. When increasing the accuracy of localization, which both monitor and book are fortuitously aligned in turn reduces the degree of the slip. Greater with a visual axis, both monitor and book may accuracy of localization simply requires the eyes simultaneously be perceived as clear, although to be more accurately aligned. not necessarily equal. (As one patient described For many patients with intermittent exotropia, his simultaneous perception, referring to dichoptic stereoscopic targets or hand-eye the diminished perceptual state of his non- targets such as placing a pointer in a drinking preferred, non-fixating eye, “My ‘big eye’ straw held parallel to the face, encourage sees one thing, while my ‘little eye’ sees the alignment. Such stereoscopic demands may other.” Such qualitative, perceptual differences prompt alignment at four or five inches in front between the two eyes may help the strabismic of the nose even though stereoscopic vision and patient keep track of the real locations of their binocular alignment are absent at traditional perceived images.) testing distances. Similarly with esotropia, the When ABC exists, the key to eliciting eyes will often align at some point in space closer stereoscopic vision is to get the patient to the face. To determine this distance, Brock21 voluntarily pointing the two foveas in the same described a test in which a penlight is slowly place at the same time so that sensory and motor moved towards a patient’s nose. Brock found information will co-vary19 and come to coincide. three responses: 1) the patient actively takes Or put another way, with both eyes voluntarily up and maintains binocular posture over some pointed at the same target, oculomotor distance, exhibiting a “centration range.” 2) The

215 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 patient exhibits a “centration point” allowing stereoscopic vision, especially in esotropes the penlight to rest at the intersection of his two prone to ABC, is peripheral awareness. Patients eyes but making no effort to maintain binocular select an area to examine. The larger the area posture when the penlight is moved on the simultaneously examined rather than examined z-axis. 3) The patient exhibits neither a centration by sequential processing and saccadic eye point nor range but actively avoids bi-fixating movements, the more “peripheral” the vision. It the penlight. Rather as the penlight approaches, is convenient to think of the area simultaneously the patient continues to over converge until, at examined as a “sphere of attention.” In actual fact, some point, the patient actively diverges, again peripheral awareness includes simultaneously to avoid bi-fixation. expanded awareness on all three axis: X, Y, and When binocular alignment is more robust, Z. For ease of presentation, Figure 2 illustrates stereopsis follows. Regarding the three groups a circle rather than a sphere of attention. The Brock identified (above), peripheral stereoscopic circle includes the screen, the floating target, vision was demonstrated within the centration the walls, and the distance between the patient range among 90 percent of the first group, 53 and the screen. Simultaneously imagining a floor percent of the second, and 13 percent of the and ceiling would create a sphere. The sphere third—who, Brock suspected, align their eyes for may be enlarged by expanding attention on the the stereo target, but not for the penlight. Brock X, Y, and or Z axis. concluded, “3D appreciation is solely a function of bi-fixation: When the eyes are not centered on the object of regard, the latter cannot be perceived stereoscopically. When they are centered, 3D is rarely absent …” With this in mind, whatever stereoscopic testing and cover testing reveals at normal testing distances during the exam is not important. Those exotropes who align their eyes at any distance for stereoscopic targets and those esotropes, with or without ABC, with gross stereoscopic vision somewhere within a centration range are typically ideal candidates for the for the therapy approach outlined below. Some patients do better attending to a In my experience it is not uncommon to find single axis; some, by attending to two or three. patients who could not perceive the stereo fly Peripheral awareness, or an expanded sphere initially, but could perceive it after therapy. of attention, may be encouraged in any number of ways: Peripheral Awareness • Begin with large targets without central As cited above, Brock suggested “aversion detail. Coach the patient to be aware of to fusion seems to be limited mainly to the the outside of the target. macular and paramacular region. For this reason • Hold the above-described large target fusion training should begin with the periphery as close to the patient as the centration and only gradually include the center.” Similarly, range permits and, again, coach the both Ludlam22 and Flax23 have reported the use patient to be aware of the outside of of binocular defocus to promote fusion. While the target. The closer a given target is, defocus may prove an initial aid in allowing bi- the more peripheral it becomes. As the fixation, another key to gaining alignment and distance from the target increases the

216 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 target becomes more central and requires encouraging the patient to look towards the more accurate alignment. center of the screen rather than alternating • Shake the target. The fovea responds attention. It may be easier for the patient to best to stationary, high contrast, targets. see simultaneously the outer boundary of the The peripheral retina responds to moving, background upon which the target appears low contrast targets. Shaking targets, or is being projected: the outer boundary of therefore, discourage foveal attention the vectogram holder, video monitor, or silver to detail and encourage peripheral screen allowing the use of polarized targets. awareness and appreciation of peripheral Divided awareness sometimes fails because, stereoscopic targets (via peripheral retinal rather than open the sphere of attention, the stimulation). patient merely alternates attention or becomes • Blur the target. Again, as reported by simultaneously aware of two small areas at once Flax and Ludlam, blur removes details without opening perception to include z-axis that encourage central attention and awareness. makes it easier for the patient to maintain peripheral awareness. It is the patient’s Gestalt Awareness attention to detail, not the details A second way to create peripheral aware­ themselves, however, which trigger ABC ness is to train the patient to see the screen as and a loss of stereopsis. Blur is a tool a gestalt. One way to accomplish this gestalt to help work around obsessive attention awareness is to ask the patient to look at the to detail. As the ability to maintain unprinted back of a business card held several peripheral stereopsis develops, blur may feet away. Most patients will perceive the be slowly reduced. Indeed, when many business card as a business card instead of esotropes first tap into the peripheral going central to see the card as a collection system they report that central details of individual edges and corners. If one of the are blurred. As peripheral stereopsis and patient’s eyes are covered and the card is slowly a peripheral lock become more second moved toward his face, at some point you may nature, patients generally learn to temper see the patient’s eye begin to move as he their peripheral awareness allowing more begins to examine the parts of the card rather and more central stereopsis and clarity than see the entire card at the same time. The simultaneously. second this occurs, make the patient aware of how it is different to see the whole card at once Three other ways are generally useful to without moving his eyes. Move the card back get the patient into the egocentric awareness out and have the patient, again, see the card system: divided awareness, gestalt awareness, as a card. When the patient can see the card and egocentric awareness. as a card, have the patient see the silver screen as a silver screen, that is, see the entire screen Divided Awareness simultaneously. When shifting into this mode of Coach the patient to be simultaneously seeing, patients often report perceptual blurring aware of the walls to the right and left of the of the 3D target and silver screen. Stereopsis target or to be simultaneously aware of the is nevertheless elicited. As mentioned above, floor and ceiling, thus “dividing” awareness. as more control of shifting from the central If the patient is unable to simultaneously to peripheral mode is developed, it generally select the two side walls to view, and instead becomes possible to achieve a balance between looks first at one wall and then at the other, the two, allowing clear seeing of more central then the peripheral vision may be elicited by targets in the presence of peripheral stereopsis.

217 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 Egocentric Awareness pencil tip to go outside the maze, the therapist A third method to get the patient would alternately coach the child to “Trace peripherally aware is to coach him to be inside the maze!” and “Trace outside the simultaneously aware of all the space between maze!” Soon the child would take responsibility his or her nose and the screen or target. The for tracing outside the maze and control the key to such egocentric seeing is to perceive pencil tip to stay inside the maze. If a child the space, not introvert to analytically estimate similarly had trouble with pursuit movements, the distance of the space in feet or meters. taking his eyes off the therapist’s moving bead, Other ways to encourage this awareness of the therapist would alternately coach the child z-axis space is to place a dowel stick next to the to “Look away from the bead!” and “Look target and have the patient, without moving towards the bead!” until the child knew when his eyes to the side, be simultaneously aware he was looking at the bead. of the entire length of dowel (a sort of “z-axis In the case of the quoit with the dot on the gestalt awareness) and the target’s position wall, once the patient has stereopsis at one compared to the dowel. If the target is close, distance, the therapist can coach the patient a finger may be used. If the target is six feet to shift back and forth between central and away, a six-foot dowel may be used. peripheral attention to teach the patient how In the case of using the dowel stick, the to shift voluntarily into the stereoscopic mode. following step by step sequence might be as The therapist can use the following instruction follows: set stressing central versus egocentric, gestalt, n Dowel close to the target or looping the or divided attention: target, thus not requiring the patient to • Be aware of the distance between your select too large of an area for viewing, nose and the dot (or be aware the silver but not encouraging central awareness of screen as if it were a business card or be the target aware of the two walls simultaneously— n Dowel further to the side of the target, whatever instruction elicits stereopsis). thus requiring the patient to open up Get the quoit to float out as far from the peripheral vision a little further dot as you can. n Dowel at the edge of the screen, thus • Now look at the very edge of the dot encouraging the patient to simultaneously (preferable with a very slight indentation see the whole screen created in it). Look at the tiny indentation n Encouraging patient to see the float of in the dot. Make your vision small and the target in relationship to the length of concentrate on the indentation. Can you the floor and ceiling, or the length of the make the quoit go flat? walls of the room. • Now be aware of the space between your nose and the dot (etc.). Can you get the For some, the use of the dowel fails because quoit to float outward again? it occludes part of the projected vectogram (e.g., quoit), thus creating a disparity between Repeat this sequence until the patient monocular and binocular cues. can take responsibility for going central and flattening the quoit and taking control to Responsibility and Control go peripheral and get the quoit to float. As The easiest way to make a patient take Birnbaum24 has described, patients often responsibility for an error is to teach the patient attribute changes in perception to the to make the error on purpose. If, for instance, apparatus rather than to themselves. Thus, a child, while tracing a maze, kept allowing his to begin with, patients may perceive that the

218 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 quoit is floating or flat as if they have nothing action, vision, and language are often learned in to do with the perception. When the central- unison—and, therefore, genuinely trusted. peripheral alternation between responsibility In the case of unexperienced actions and control procedure is complete, the patient (actions never directed by the visual process), should take responsibility for making the quoit language again reduces to abstraction, analogy, go flat and know that he is in control of the quoit or metaphor. The words are not understood floating. Also, the patient’s learning to create a in the fullest perceptual sense any more than lack of stereopsis on purpose generally allows a non-surgeon understands surgery in the him or her to create stereopsis on purpose. The fullest perceptual sense. If, for instance, a seer patient needs to understand that the float of the depends on sequential processing rather than quoit is in the patient, not the quoit. simultaneously selecting larger areas of space to view, then he may have no perceptual understanding of the difference between the Identification ing phrases “seeing a room with things in it” and Center “seeing individual things in a room.” He may Vision be able to repeat or comment on the words,

but the perceptual distinction between the two Anti - Gravity -Auditory phrases may elude him.

Speech Brock was aware of the restriction of language for those unaccustomed to experiencing Figure 3—Skeffington’s Four Circles stereopsis: When stereoscopic fusion prevails, the Language patient is conversant in our language and Optometrists have noted language’s role in when stereoscopic perception is absent he vision at least since the time that optometric speaks a foreign tongue which most of us pioneer and educator A.M. Skeffington, as legend simply do not understand. For this selfsame has it, captured the visual process by scribbling a reason we misinterpret his statements by four-circle Venn diagram on a napkin. The circles applying them to our own mode of seeing (see Figure 3) included “centering” (selecting instead of to his.25 an area of space for attention and meaning), “identification” (the process by which one knows Consider an example or this breakdown what things are), “anti-gravity” (sense of body of language. Suppose the patient is viewing position/movement), and “speech/auditory” the quoit and dot target on the wall and the (language/analysis of sound). Metaphorically therapist asks, “Which is closer, the dot or speaking, vision emerges to become greater the quoit?” The patient replies, “The quoit.” than the sum of the four circles for the purpose Asked, “If you were to walk down to the wall, of deriving meaning and directing action. which would you come to first, the quoit or the In abstract language, such as the phrase dot?” the patient again replies, “The quoit.” “counting all the stars in the universe” real Similarly, when asked, “Where is the dot?” action and vision are abandoned for analogy or the patient will correctly answer, “On the metaphor. The metaphor may inspire action or wall.” But when asked, “Where is the quoit?” mental images, but you can neither count nor the patient may answer, “On the wall.” This accurately imagine all the stars in the universe. last response at first seems to contradict In concrete, perceptual language, such as the the previous three, but actually the patient phrase “picking up the marble,” language is is correct. In the illusion, the quoit may be merged with vision to direct action; in fact, such perceived closer than the dot, but in actual

219 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 fact, both the quoit and dot are physically on note what your eyes feel like as you see that the wall. If the patient were to walk down and illusion even though it conflicts with what your touch them, his or her hand would confirm hands would normally tell you is true.” Even the correctness of the response. if the patient has not voiced his concerns, he One way to explain this behavior is that to often feels confused with the whole endeavor. the strabismic patient, the question “Where?” The therapist’s communicating about the means, “Where would my hands and body (not difference between eye information and hand my eyes) tell me the target is?” This would information may be useful. At the very least, be only natural if the patient, to correctly such communication signals to the patient that understand the world, had come to ignore the therapist understands the patient’s dilemma perceptions that conflict with his hands. Since between the illusions of binocular input and dichoptic illusions conflict with hand-body input, habitual body action in habitual space. With the patient ignores the stereopsis illusion, just such language-confused patients the therapist as he ignores such illusions as luster, rivalry, or should continue with the “seem to be” rather superimposition, any one of which could result than the “is” instruction sets. in constant confusion and diplopia. Instead the Having considered some general sugges­ patient perceives what past actions have proved tions for dealing with expanding the size of to be true. Visual illusions lie; the hands do the sphere of attention, taking responsibility not. The response is not unlike asking a person and control, and dealing with language, we to look at a photograph of a dog standing in consider the use of some actual dichoptic front of a fire engine. To the question, “Which targets in developing stereopsis in strabismus. is closer, the dog or the engine?” the viewer would answer, “The dog.” But when asked to Vectographic Stereoscopic Vision “touch the dog” and “touch the engine,” the Traditionally, at least since the time of viewer would correctly touch both on the same Brock, red-green anaglyphs have been used plane. The adapted strabismic is likely no more to create dichoptic stereoscopic vision in the tricked by the quoit binocular-cues illusion treatment of strabismus. Since most patients, than the photograph viewer is deceived by the in the author’s experience, have an easier photograph monocular-cues illusion. time perceiving vectograms than anaglyphs, To work around the language problem, this paper will stress vectographic and, Brock suggested the following approach: with the exception of red-blue computer- I, therefore try to explain to my squint generated randot stereograms, largely ignore patients how their mode of sight differs from anaglyphic procedures, not that the training ours and what strange visual falsifications tools suggested below could not be done they have to expect before they may gain anaglyphically. normal binocular vision.26 Quoit with Dot at Near In the case of the quoit and dot the A great tool for eliciting stereoscopic therapist might explain, “You’re right. Both the vision in esotropia is a quoit vectogram with a quoit and dot are actually on the wall, but the nickel-sized dot on the clear plastic handheld overhead projector and the glasses can make vectogram holder. While the quoits are things seem different than they really are. dichoptic, one being seen by each eye, the dot When I’m asking you where the quoit is, I’m is real. Both eyes are seeing the same dot as a not asking where the quoit really is but where it point of reference. seems to be. The quoit’s position is an illusion. When beginning, especially with a younger It is not real. We are developing your ability to patient who is unfamiliar with the apparatus,

220 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 • Ask the patient to see the entire plastic holder simultaneously as if it were a business card (gestalt attention). • Ask the patient to be aware of how much space there is between the dot and his Figure 4: Demonstration of nose (egocentric attention). Quoit Behind Dot While any of these approaches may be useful in eliciting EDP (egocentric depth perception), the patient’s responses often give clues whether he is in the relative/central or egocentric/peripheral mode. For instance, the therapist holds the clear-plastic holder with when the quoit is at 3 (base out disparity), the dot in one hand within the centration range patient may report that the quoit is in front, but (see Figure 4) and, with the other hand, places at C (base in disparity) report, “Now the dot is in both superimposed right and left quoit slides front.” This response suggests that the patient physically first in front of the holder and then is attending to RDP (relative depth perception) behind it, asking the patient if the quoit is in rather than EDP. The perceived z-axis position front or behind the dot. When the patient has of the dot should not be moving because the demonstrated an understanding of “in front true position of the dot is not changing. The of” and “behind,” the therapist inserts the two perceptual position of the moving quoit should quoit slides into the holder, centering them be changing. If the patient is in the egocentric around the dot, and disparates the right and mode, he should perceive the quoit moving left slides repeatedly between C and 3. Note in front of and behind the dot compared to here that the therapist is not trying to build himself. Asking the patient to attend to the ranges, which would cause the eye to deviate space between his nose and the dot, generally and could invite an ABC response. Rather the shifts him into the egocentric mode, stabilizes therapist instructs the patient to watch the dot the absolute position of the dot, and allows the with aligned eyes, disparates the quoits, and patient to perceive the quoit moving in front of asks the patient about the perceived relative and behind the dot. positions of the dot and rope. Once peripheral awareness has been trained The area of space selected for viewing may to maintain grossly aligned eyes through some be increased by using a number of approaches range of z-axis movement, the goal is to make suggested in the above peripheral vision the target more central. The closer the holder section: is to the patient’s face, the more peripheral the • Shake the two quoits compared to quoit is and generally the more accurate the the dot even while moving the quoits localization. As the vectogram holder is moved relative to each other between 3 and C out farther away from the patient’s nose, the (peripheral retinal stimulation). quoit and dot become a more central target. • Ask the patient to look towards the dot Also if the eyes are not diverging as the target but to be aware of the shaking quoit out recedes, the angle of strabismus is increasing of the corner of his eye (peripheral retinal relative to the dot. Such factors cause the stimulation). perception of the position of the quoit to • Ask the patient to be aware of the whole become confused. Thus, the patient is definite room while judging if the quoit is in front about the quoit’s position when it is near. As the of or behind the dot (divided attention). dot is moved farther away and into the “zone

221 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 of confusion,” the patient is no longer certain wall but, having entered the zone of confusion, of the quoit’s position. Rather than being able will no longer be certain of the quoit’s position. to circle the quoit with a finger or pointer As outlined above, a number of instruction sets accurately, the patient gives vague reports and variations of physical parameters can be such as, “the quoit seems to be somewhere used to manipulate peripheral awareness and in front of the dot.” Also, for a given base-out elicit the patient’s perception of stereopsis and disparity, the farther the dot is moved away correct stereo-localization: from the patient, the greater the amount of • Start closer to the wall. Coach the patient float the quoit should appear to have relative to “look toward the dot, but keep your to the dot. The therapist knows the zone of attention focused on the entire ring at confusion has been reached when, as the dot the same time.” is gradually moved farther from the patient, • Gradually move farther away until certain the patient begins to perceive the relative localization is lost. distance between the quoit and the dot to be • At a distance where the patient has stabilizing or even decreasing, as if the quoit is some perception of the ring’s float, work now retreating back closer to the dot. “responsibility and control,” alternately having the patient go central to lose the Quoit with Dot on Wall float and then go peripheral to regain Using an overhead projector, the therapist the float. projects the quoits with the dot target onto • Cover one of the patient’s eyes and lose a silver screen that does not depolarize the the EDP. Uncover the patient’s eye and light. This target is half natural (the dot is regain fusion and EDP. seen simultaneously by both eyes, as are the • Have the patient look at his finger held a contents of the room) and half dichoptic (each few inches in front of his face. Then have eye is exposed to a different ring). The therapist the patient return his attention to the positions the patient so that both eyes may be screen, become peripheral, and again grossly aligned on the projected dot. If this see the float. requires the patient to move too close to the • Coach the patient as follows: screen, then the shadow of the patient’s head n “Be aware of the right and left walls at can serve as the dot. the same time.” (divided attention) As the patient views the dot, the therapist n “Be aware of the floor and ceiling at disparates the quoits between C and 3, base in the same time.” (divided attention) and base out (again the therapist is not building n “Be aware of the distance between ranges, but introducing disparities so that your nose and the dot.” (egocentric each eye’s slightly different perspective elicits attention) stereopsis). The patient is coached to increase n “Be aware of how long the floor is the size of his or her sphere of awareness and between yourself and the dot.” to report if the quoit appears to be in front of (egocentric attention) or behind the dot. After correct stereoscopic n “See the entire silver screen simultane­ vision is achieved with the patient standing ously as if it were a big silver business closer to the dot on the wall, and the patient card.” (gestalt attention) has a certainty of where the quoit is floating, n “Constrict your attention to the very the therapist can coach the patient as far away edge of the dot and make the quoit go from the wall as he can maintain certainty of the flat on the wall. Now, see the side walls quoit’s location. Past that distance, the patient (entire screen, the space between you may be able to report that the quoit is off the and the dot—whichever works) and

222 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 make the quoit float.” (Responsibility may interfere with the perception of and control) stereopsis due to the conflict between • Arrange the room physically to increase monocular and binocular depth percep­ appreciation of stereopsis in the following tion cues when the dowel overlaps a ways: portion of the quoit. n Adjust the overhead projector to blur n Have the patient use a shorter, lighter, the quoit. Gradually reduce the blur as dowel stick to tap the longer dowel stick stereopsis and correct localization can at a point even with the perceived ring. be maintained. Thus if the patient perceives the quoit n Shake the quoit to encourage peri­ as being close to the wall, he will tap pheral awareness (peripheral retinal the one stick against the other at that stimulation). distance, etc. n Place a chair between the patient and the dot and have the patient be Projected Spirangle peripherally aware (as described above). Stage I—Peripheral Stereoscopic Vision Compare the location of the quoit Once the patient can alternately voluntarily to the chair back in order to increase choose to appreciate or not appreciate z-axis awareness. At first, the patient’s stereopsis with correct localization several constricted sphere of awareness may feet away from the wall, we are ready to try require the chair to be aligned directly the spirangle vectogram. To begin with, the with the quoit. As the size of the therapist adjusts the overhead projector to sphere of awareness increases, allowing blur the projected spirangle until its form is simultaneous awareness of the chair vague and its letters and other details are and ring, the therapist can move the beyond recognition. Encouraging peripheral chair further to the side to increase awareness, the therapist shakes the vectogram x-axis awareness. and encourages the patient to discern if the n Align more than one chair along outside or the inside of the spirangle is closest. the patient’s z-axis to extend z-axis When the patient is able to see the float, the awareness, stereopsis, and correct therapist adds the responsibility and control of localization. central-peripheral alternation until the patient n Arrange two chairs between the patient can control the appreciation of stereopsis and and the screen, but place one to the localization with the blurred target. Then the right side and one to the left side of therapist reduces the blur until the patient the screen. Coach the patient to be perceives the target to begin to flatten. The simultaneously aware of the two chairs, therapist blurs the target just enough to the dot, and the floating quoit. restore the EDP and coaches the patient to n Have the patient hold a long dowel use peripheral awareness—especially gestalt stick between himself and the dot attention of the complete silver screen—to keep on the wall. Have the patient try to the spirangle floating, even as blur is slowly see the entire length of the dowel reduced. Indeed, the goal of the spirangle simultaneously. With the aid of the dowel is to teach the patient to use peripheral stick, while the therapist continues to awareness to maintain the target’s float despite shake the ring, the float can become the introduction of central detail. Apart from quite dramatic. Alternatively, for some the central-peripheral attention procedures patients, awareness of the side wall can encouraging responsibility and control, digital be more useful: Recall that the dowel instrumentation is often more helpful in the

223 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 development of peripheral attention in the Digital Stereoscopic Vision presence of central stereopsis. For digital therapy, we use the Computer Orthoptics® Liquid Crystal Automated Vision Stage II—Central Stereoscopic Vision Therapy System (VTS4).27 While the images of Once the patient has good appreciation the VTS4 are dichoptic, the VTS4 procedures of spirangle stereopsis with the vectogram can be performed to stress real images in perfectly clear, the therapist can direct the the real world as well. When, for instance, to patient’s attention to the alphabet within the increase peripheral awareness and egocentric conical structure of the target, with lines which stereopsis, attention is directed to awareness of spiral outward from center to periphery. Each of the instrument framing the screen and images, these larger letters is in a circle and surrounded both eyes are seeing the same frame. by a square, as shown in Figure 5 (not to be While the projected quoit vectogram has confused with the tiny letters with suppression certain advantages over the VTS4—being easier controls at the spirangle’s center and end). to blur without lenses and being better suited for working responsibility-and-control for alternate central-peripheral awareness—the VTS4 has a number of advantages over projected quoits: • The liquid crystal glasses are flashing rapidly between the right and left eyes’ images, making it difficult not to perceive the stereopsis—a feature which makes Depending on whether the circle has base it more difficult to voluntarily flatten out, base in, or no disparity relative to its the stereopsis with central awareness. square, the circle should be perceived as closer, (The rapidly changing stimulus is similar farther, or in the same plane as the square in impact to shaking the quoits.) This (respectively). With letter A, for instance, the persistence of stereo nevertheless circle containing the letter should be perceived provides a boon for many of those who in the same plane as the square; with letter cannot otherwise perceive stereoscopic B the circle should be perceived closer than vision. the square; with letter C the circle should be • Unlike the projected quoits, the VTS4 perceived behind the square. allows the patient to get very close to As the patient searches for the alphabet the screen without occluding the target, and perceives if the circle is flat, in front of, thus the VTS4—like the quoit with dot at or behind the square, the therapist needs to near—allows a more peripheral target at coach to patient to continue to see the entire a distance where the esotropic patient’s spirangle floating out in space. Thus the eyes are closer to being aligned. procedure combines EDP and RDP, as well as • The VTS4 provides a wide variety of spatial language. targets, some more peripheral, some Not all patients who can perceive some more central, all of which can be varied in degree of float on the quoit will be able to size to make them even more central. perceive the float on the spirangle. Not all • The VTS4 also allows an excellent bridge patients who perceive the float on the spirangle for coming to appreciate 3D TV, it being will be able to perceive the relative position possible to connect a Blu-ray 3D Player to of the circles and squares. Thus it is possible the same computer system. for patients to develop decent EDP while still lacking central RDP.

224 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 The best targets for initially eliciting the absolute depth of the target floating stereoscopic vision are the ring, the dog and ring, out into the room. and the robot and ring. The same techniques • As stereoscopic fusion improves, add that were used for the projected quoits may covering and uncovering one eye or be used for eliciting peripheral/egocentric looking back and forth between a near localization for these VTS4 targets: finger and the screen. • Being aware of the entire room to the sides of the instrument (divided attention) The patient works these peripheral ring • Being aware of the distance between targets until maximum float is obtained using nose and target (egocentric attention) either rectangular screen frame gestalt attention • Being aware of the rectangular gestalt of or egocentric attention. Next the airplane- the screen frame as if it were a business alphabet target and then the dolphin-fish target card (gestalt attention) may be used to better combine RDP and EDP. • Pressing the Function 11 key to cause the The therapist fully increases the size of the ring to rapidly oscillate (peripheral retinal airplane-alphabet target and has the patient stimulation). remain aware of the screen frame gestalt until the patient can see the target’s blue background In addition, a number of other techniques closer and further than the screen frame as the may be used to facilitate appreciation of target is varied between base-out and base-in stereoscopic vision: disparity. It is often the egocentric localization • Making the ring larger or smaller to of the blue background that allows the patient optimize appreciation of stereoscopic to overcome the central details encouraging a vision at a given distance. A ring that is return to strabismic posture and loss of RDP. larger than the patient’s ability to open As with the circle targets, the dowel stick up side vision is ineffective. A ring that is or neoprene toy sword may be placed closer too small triggers strabismic posture and to individual letters of the airplane-alphabet adaptations. target to encourage perception of egocentric • Placing both hands on the screen, one on localization. The patient should be encouraged each side of the ring, being aware of both to perceive simultaneously the entire length hands at the same time, and being aware of the sword or dowel, that is, should be of the length of both arms. encouraged to see the gestalt of the sword • Placing the tip of a dowel (or neoprene rather than running eyes up and down its length foam sword, to protect the screen surface) to build a sequential perception of the sword; near the ring or other target to facilitate sequential perception frequently defeats both appreciation of stereoscopic vision without EDP and RDP. the need to fully expand the sphere of The fish target may be used the same as the attention and open up peripheral vision. alphabet target, again seeing the position of the Once the stereopsis may be appreciated pale green background compared to the gestalt with the sword close to the target, the of the frame edge. Whereas the alphabet target therapist positions the dowel increasingly matches monocular and binocular cues, with farther to the side until the patient can letter size corresponding to letter distance (so open up side vision enough to use the the patient’s responses of depth can be based rectangular screen frame gestalt to elicit entirely on monocular cues), the fish target egocentric localization. The goal is for the does not necessarily match size and distance. patient to be able to perceive not only Thus it requires stereoscopic appreciation and the relative depth within the target, but gives a more reliable guide of the patient’s

225 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 binocular illusion status. (The stationary ‘Figure-8 My therapists and I typically begin with the Racetrack’ vectogram also varies size and depth second track of Madagascar III. We stop the independently.) movie with the animated television set in the As digital stereo targets can be seen at scene flying out at the patient. We prompt the greater distances from the monitor, their patient to be aware of the outside of the screen appreciation can be combined with such and appreciate the egocentric position of the traditional movement activities as leg swings animated television set in space. We next stop while balancing on one foot, walking rails, the action of the film with the monkey in the balance boards, or infinity walk28—all without wig applying makeup. Again, we encourage loss of correct localization. awareness of the edge of the screen and perceiving the egocentric position of the Computer-generated Randot Stereograms monkey’s lips. Finally, we stop the movie when With strabismics who are truly intermittent, the pillow explodes into a cloud of floating their eyes being precisely aligned rather than feathers, and we train the patient on being grossly aligned when straightened, computer- aware of how attention to the outside of the generated randot stereograms can be used. As screen gets the feathers to float out further. designed, the randot stereograms stress RDP, a Once the patient has seen the animated smaller square being perceived to float outward flying television, the monkey applying lipstick, from a larger rectangle. When these randot and the floating feathers in 3D, we replay track targets are used, however, care must be taken 2 without stopping it, encouraging awareness not to forget EDP. If the patient “gestalts” the of the outside of the screen and perception rectangular edge of the computer screen, as of the RDP and EDP in the scenes without practiced during previous digital procedures, stopping the action. We then jump ahead to the patient should perceive SILO of the larger track 12, again stopping the action throughout rectangular background moving behind the the circus scene, getting the patient aware of screen and in front of the screen even as the all the 3D moments before replaying the scene. smaller square floats relative to the rectangle. While doing this, we encourage the use of all The larger rectangular target should float the tools learned in the therapy room during into the screen and get larger during base-in vectographic and digital presentations: vergence and float outward and get smaller • The dowel stick or neoprene sword can during base-out vergence. In this way randot be inserted in the scenes to encourage stereograms can also be used to integrate 3D perception while still allowing a RDP and EDP, which can later be transferred to constricted sphere of attention. Ideally, natural conditions, as we will see in the “Natural by the time 3D television is used, the Stereopsis” section below. patient has already learned to expand the sphere of attention to include the 3D TV gestalt of the screen edge and expected The VTS4 has any number of targets EDP for the movie scenes. working evermore central stereopsis. These • The patient can stand at greater distances targets can and should be used to develop from the screen. stereopsis further, but once RDP and EDP can • The patient can cover an eye and be maintained on the airplane and dolphin uncover it to compare the stereopsis targets without triggering strabismic posture while also learning to regain fusion after and spatial confusion, 3D movies can be used dissociation. for further practice in both RDP and EDP, both in office and at home.

226 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 The same principles can be applied to epiphenomenon, for instance, because it adds any other 3D movie that makes use of both no propulsion to the bee’s flight. The term is crossed and uncrossed disparities. When popular in a philosophy that proposes that working 3D television movie perception the visual consciousness adds nothing to visual therapist needs to be aware of the times when action. The argument is that since actions— maximum base out disparity is encountered to like a tennis pro’s swing—come before any be sure it is properly perceived by the patient. conscious analysis of the action, consciousness Wikipedia provides a “List of 3D Films.”29 The lags behind the action,31 consciousness (that is, list tells if the movie was filmed in 3D or filmed conscious free will) is too slow to affect action. It in 2D and converted to 3D. Converted movies may be true that consciousness played no part typically contain little base out disparity with in the reflex action. However, whether conscious which to check localization. Most animated films exploration may have played an active part in are filmed in 3D and have both BI and BO, or learning the swing is not considered. In the same crossed and uncrossed, disparity. way, even though consciousness of stereopsis Once the patient demonstrates accurate 3D may follow rather than lead visual action it does movie perception in the office, the therapist can not necessarily exclude conscious exploration assign 3D TV movie viewing at home and 3D of stereopsis as a tool for teaching comfortable movie viewing in the theater. An adult patient alignment. Despite a century of disagreements can be trained to ask herself periodically, “Am between those promoting the surgical I aware of the border of the screen.” “Am I versus nonsurgical tools for the treatment of aware of the distance between my nose and the strabismus,32 my experience with vision therapy screen?” “How far off the screen are the images certainly supports this second view. popping?” If the patient is a child, a parent can be trained to ask the same questions. Mechanical versus Localization Alignment Physiologically speaking, there is more than Natural Stereopsis one way to align an eye. Maddox, in 1893, The reason we work dichoptic stereo classified vergences as tonic, accommodative, perception is not to familiarize the patient with disparity, or psychic (such as voluntary and binocular illusions, which may have no benefit proximal convergence).33 Lenses altering beyond entertainment in the office or movie accommodation can be used to alter theater. We use stereoscopic vision procedures vergences. In the treatment of strabismus, I find to train improved localization, which the patient it convenient to divide non-accommodative may use to encourage alignment and improve vergences into two practical classifications: performance. Unless, however, this awareness mechanical vergence and localization vergence. is carried beyond the confines of the therapy What I am calling mechanical alignment is the room, the treatment may be for naught. It is, use of vergences to avoid diplopia (disparity) therefore, useful to transfer what the illusions and encourage voluntary alignment (psychic). teach in the therapy room to real stereopsis in I can, for instance, voluntarily cross my eyes the real world. and control the separation of diplopic images Despite the advantages of stereopsis, even in space. This method, however, requires that I this goal is not beyond criticism. The surgeons learn to divorce accommodation from vergence Von Noorden and Campos,30 for instance, have if I am to see clearly with crossed eyes (absolute written, “Stereopsis is an epiphenomenon of presbyopia helps). normal binocular vision.” An epiphenomenon Most exotropes and many esotropes similarly is a byproduct of an action that adds no can voluntarily align their eyes, using voluntary benefit to the action. The buzz of a bee is an convergence or divergence. The problem is

227 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 that while using such mechanical vergences Thus each time the patient is about to insert strabismics are often not comfortable without the stick in the straw, the therapist reminds considerable training, including the use of base- the patient to “see the distance between your in and base-out prisms to train convergence and nose and the straw” or asks, “Can you see how divergence, as well as monocular and binocular much air there is between your nose and the accommodative rock to ensure full flexibility straw?” In this way the therapist is encouraging between accommodation and vergences. z-axis-egocentric awareness in the appreciation Patients using mechanical vergence expend of stereopsis to help trigger alignment. The concentration and effort that often results in goal is to turn localization vergence into the stress. Unless the desire for cosmetically aligned primary strategy and mechanical vergence eyes outweighs the inconvenience of the into a secondary strategy for fine-tuning ocular stress, mechanical vergence alignment is often alignment if necessary. abandoned. I propose a second approach to align eyes: Brock String localization. Localization vergence similarly relies Physiological diplopia can be an artifact on both disparity and psychic vergence, but in of extending the z-axis sphere of attention, a different way. Here, disparity is used in the causing the object fixated to be seen single creation of stereopsis rather than the avoidance and objects aligned closer and further to be of diplopia. Here, the eyes are aligned where seen double. If a Brock string—a several-feet- the patient knows the target to be compared or-more-long string with three beads on it—is to self. Thus EDP plays a major role. While extended outward from the patient’s face, and mastering the exercises designed to increase the patient extends z-axis awareness to see accommodative and vergence flexibility and the entire length of the string simultaneously, comfort remains as useful as ever in achieving physiological diplopia may create the illusion alignment, if the patient learns to utilize of two strings crossing each other to form an X, localization from EDP, then alignment is far less the intersection of which occurs at the point of stressful. With this goal in mind, we turn to the bi-fixation, the distance at which the patient’s art of transferring dichoptic stereoscopic vision eyes are converged. (As discussed previously, to natural stereopsis. the sphere of attention, also allowing the physiological diplopia illusion, can often Binocular Stick and Straw be expanded, depending on the patient’s When performing the binocular stick and idiosyncrasies, using simultaneous gestalt straw procedure, the patient inserts a pickup awareness of the string length, egocentric stick in a drinking straw held parallel to his/ awareness of the distance between nose and her face. The procedure encourages alignment string end, or divided awareness of the walls to and perception of stereopsis for its completion. either side of the string.) If mechanical vergence is the primary strategy If for instance the string beads are placed at being used, the patient voluntarily aligns four inches, ten inches, and forty-eight inches his eye on the straw while inserting the stick from the patient’s nose, and the patient’s eyes into the straw. If instead, the patient is to use are bi-fixating the middle bead to create the localization vergence, he is coached to expand normal illusion, the patient will perceive the the sphere of attention to include the previously bi-fixated bead as single and the beads closer learned z-axis awareness to judge the distance and farther double. If alternation is artificially between self and straw. The awareness helps suspended by command, and the esotropic trigger alignment, reducing the effort typically patient with ABC is bi-fixating the ten-inch needed to produce mechanical vergence. bead, he can typically be encouraged to behold

228 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 the physiological diplopia illusion inside the bi- seeing. Furthermore, while esotropes often fixation point, but he perceives no such illusion avoid bi-fixation when their eyes are diverging, at greater distances (typically perceiving a approaching from the near side of the target, bi- single string perpendicular to his face beyond fixation is frequently better tolerated when the the bi-fixated bead). Such a patient will perceive eyes are converging, approaching from farther two strings converging into the ten-inch bead to closer, possible because the esotrope has and a single string in its true position beyond no previous experience inside of the centration the point of bi-fixation. Similarly, the patient point leading to adaptation and avoidance of will see the four-inch bead inside the bifixation bi-fixation. point as double and the forty-eight inch bead Since the bead will appear single, even if beyond the bi-fixation point as single. Thus the the esotrope over-converges, care must be patient sees a Y rather than an X. taken that convergence halts, the three strings The goal of the Brock string, however, is intersect, and bi-fixation occurs exactly at the not to illicit the physiological-diplopia illusion. bead. Once such bi-fixation has been mastered, Apart from the string being an excellent appreciation of egocentric and relative depth tool for the development of z-axis gestalt perception may be added by performing a awareness, the goal of the string is to use modification of the Brock string procedure. the illusion to provide feedback for bi-fixation while expanding the sphere of attention along 3D Stick and String the z-axis. Note that the perception of the The Brock string is modified into a 3D strings intersecting as a ‘Y’ is as useful for this procedure by having the patient, while feedback as the perception of the intersection maintaining bi-fixation, be aware of the length as an ‘X’! Thus there is no reason for teaching of the strings running into the bead, or be the esotrope with ABC to see double beyond aware of the amount of space between the the point of bi-fixation — which could translate patient’s nose and the bead. The bead is now into seeing double in the real world — when substituted for the straw in the above-described it is not necessarily useful to do so. Instead stick-and-straw procedure. The patient holds esotropes can be trained to bi-fixate a bead a pickup stick parallel to his face and several once they have already been trained to diverge inches to the side of the bead. While the patient as far as the strabismus allows (with free space maintains egocentric localization and perceives jump vergences and peripheral awareness). The the three strings intersecting at the bead, he instructions for working with the Brock string uses the stick to touch the side of the bead just while perceiving a ‘Y’ intersection are: as in the stick-and-straw procedure, where he • Throw the eyes maximally outward to placed the stick inside the straw. To accomplish make the three strings meet as far behind this, both EDP and RDP are coordinated, the bead as possible. the egocentric stereo forming a base for the • Then converge just until the bead relative-stereoscopic stick-andbead placement. appears single, with the three strings Once the patient is learning to coordinate intersecting at it. eye position, stereoscopic perception, and hand movement by simultaneously bi-fixating Developing physiological diplopia inside the the bead, perceiving the illusion of three centration point typically offers little problem, so strings meeting at the bead, and accurately long as the patient is not alternating to maintain directing the stick from the side of the bead to strabismic posture. The esotrope’s visual world contact the bead, the therapist begins varying is beyond, not inside of the bi-fixation point, the distance of the bead from the patient’s so the diplopia does not transfer to everyday nose, placing the bead at various distances

229 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 within the patient’s centration range. Thus if appreciation of stereopsis outside the therapy the patient’s range of bi-fixation were between room. two and ten inches, the therapist would place If you hold a hand mirror before your face, the bead at two inches then ten inches, then you may count a few of your eyelashes in the six inches, etc. At the ten-inch distance, the reflection. If instead of concentrating on such patient would get the three strings to intersect central vision, you open your side vision and at the bead before making the placement. At become simultaneously aware of the gestalt closer distances, the therapist would have the of the mirror frame encircling the glass, you patient diverge behind the bead and slowly should become aware of the actual location converge until the two images of the bead just of your reflected face floating as far behind came together. This completed, the patient the glass as you are in front. At this point, would again open up egocentric attention and instead of being locked in RDP and noting make the stick placement. that the reflection of the tip of your nose is The above procedure can be repeated with closer than the reflection of your cheeks, you the string slanted to the right, left, up, and have extended your sphere of attention to down compared to the previous straight-ahead become aware of EDP and the position of position. We want the patient to be adept at bi- your reflection compared to actual space. fixation, EDP, RDP and eye-hand coordination When working with strabismus, the therapist in all fields of gaze where binocularity may exist. may use this stereoscopic phenomenon in the same way that the quoit and dot were used. Vertical Stick and Straw By encouraging the patient to “see the room Vertical stick and straw procedure is just to both sides of the mirror” or “see the entire an extension of binocular stick and string. In mirror frame at once” or “see the space between this activity, however, instead of using a bead you and the mirror frame” the therapist can on the string, the patient uses a vertically-held coach divided, gestalt, or egocentric awareness, drinking straw aligned parallel to the face. As whichever best expands the sphere of attention with the bead, when the patient’s eyes are and result in EDP. To work responsibility and aligned beyond the straw, the patient should control, the therapist can encourage the patient perceive the illusion of the straw being double. to alternate between center and periphery, If the patient has already mastered control of constricting awareness to a single eyelash and vergences using the string, the therapist now then expanding awareness to the rim of the coaches the patient slowly to converge until mirror frame and the egocentric position of the the two straws just came together, again being reflection in space, some distance beyond the careful not to allow convergence nearer than mirror frame. the bi-fixation of the straw. The patient, holding While working the hand-held mirror pro­ the stick vertically above the bi-fixated straw, cedure, the therapist can check for accurate lowers the stick into the straw. As with the location of the reflected image by moving a string, the placements would be repeated at hand toward the patient from well behind the all distances that the patient can look beyond mirror. The patient is coached to simultaneously the straw, double the straw, and converge to (without shifting his eyes back and forth) be fuse the straw before making the vertical stick aware of his reflection and your hand and note placement. when the hand and reflected image are at the same distance from his face. The absolute Hand Mirror Stereopsis position of the reflected image should change Mirrors provide another means for manipu­ as the distance of the mirror from the patient’s lating the sphere of attention to transfer face changes. To check the localization of the

230 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 mirror image, the therapist simply has to observe If when asked to see the frame gestalt, if the reflected image is as far behind the mirror the patient moves his eyes about the frame to as the patient’s face is in front of the mirror. If view it sequentially rather than simultaneous­ not, the therapist should coach the patient to ly, the therapist should encourage him to look expand his sphere of attention, using whichever toward his reflection and see the entire frame method works best. Inaccurate localization simultaneously out of the corner of his eyes. As signals that the sphere of attention is contracted explained in the gestalt awareness section, he or that the patient’s eyes are not aligned. In the should view the gestalt of the frame just as he case of an esotrope, the therapist can move the would view the gestalt of a business card. This mirror closer to the patient’s face to secure more awareness should not be difficult if it has already accurate alignment. been worked extensively with dichoptic vecto­ Because the mirror can be held mere inches graphic and digital images. in front of the face, the procedure is useful for If the patient is successful at shifting into the esotropia as well as exotropia. The expansion of egocentric system, he should see his reflection the sphere of attention can also be manipulated spring back as far behind the frame and glass as by changing the mirror size, larger mirrors he is standing in front of the mirror. If not, (and requiring a greater expansion. Similarly, the the patient’s eyes are aligned or approximately closer a given size mirror is to the face, the aligned) it is likely the patient is still processing more peripheral the patient must become to centrally (or his eyes are not really aligned). If be simultaneously aware of the entire frame the patient is not able to expand his sphere of encircling the glass. attention out as far as the edge of the mirror frame, have him approach the mirror and Wall Mirror Stereopsis place his hands at shoulder width on the glass. The following mirror stereopsis procedure Have him wiggle the fingers of both hands is useful for intermittent exotropes when their simultaneously and be simultaneously aware of eyes are aligned. It is also useful for intermit­ both hands’ finger movement while watching tent esotropes, or esotropes with approximate­ the reflection of his face behind the mirror. ly aligned eyes and peripheral fusion. Such Ask the patient if he can now see his reflection alignment or partial alignment should already behind the glass of the mirror compared to have been taught using dichoptic images as his hands. This modification allows the patient explained in the above sections before at­ to open up his sphere of attention less and tempting this procedure. still shift into the peripheral mode of seeing. With the patient several feet in front of a Providing that the patient is simultaneously wall mirror, have him examine the features of attending to both hands and the reflection of his face—nose, eyes, chin, eyebrows. While his face rather than sequentially attending to performing these central observations, most hands and face, he should appreciate EDP. patients will be aware of the details of their Another way to open the sphere of atten­ faces, not the position of their reflections in the tion is to place two strips of masking tape mirror. To expand the patient’s sphere of at­ on the mirror, one strip to each side of the tention and get him into the EDP system, have patient’s reflection. The patient then watches the patient shift attention to perceive the ge­ his reflection while being simultaneously stalt of the mirror frame and be aware of how aware of both strips. This will often allow far his reflection is behind the frame and glass. the patient to shift into the peripheral mode Most patients will instantly see their reflections and perceive EDP. The tapes are especially spring behind the glass. useful if the patient is practicing using a wide

231 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 bathroom mirror at home when shaving or and plays a game with his son, chasing him applying makeup. around the room, and warning him to beware Once the patient has opened his sphere of “the claw.” These scenes inspire a useful of attention to become aware of the distance therapy procedure: his reflection is behind the mirror glass, the If you raise your hand with its palm vertical therapist can stand behind and to the side of to your face and then curl your fist so your the mirror and have the patient move up or fingers and thumb are all pointed at your back until the patient’s reflection is beside the eyes, you will be viewing “the claw.” If you therapist. To accomplish this, the mirror must view this claw first with one eye, then the either be freestanding or positioned next to other, then both, you will see that each a doorway or hall so the therapist can stand eye perceives a different image and when in the next room. The therapist then moves both eyes are opened simultaneously closer or farther behind the mirror, and the these two different images are combined patient, using EDP, can move closer and farther into a stereoscopic perception in which the in front of the mirror to continue to perceive the fingers appear longer as they perceptually image of his reflection beside the therapist. spring out closer to your face. This I call, Once good localization has been obtained, “Claw Ste reo p si s.” the patient can become aware of mirror stere­ opsis in routine life whenever a mirror is used. If the patient places “the claw” in front of his face, directs both eyes at the nearest Mirror Near-far Jumps or Mirror Cover/ fingertip, becomes aware of how far that Uncover/Recover fingertip is in front of his nose, and extends Once the patient has demonstrated his vision to simultaneously be aware of accuracy in perceiving the mirror image, the the length of the fingers and position of procedure can be combined with near-far his palm, the stereopsis will become even jump vergences or cover/uncover/recover. more apparent. With near far jumps, the patient looks at his finger two or three inches in front of his Just as a wall mirror can provide a stereo nose and then looks back into the mirror to target to give feedback for alignment in locate his image behind the glass. In the case distance, “the claw” can provide a natural of cover/uncover/recover, the patient covers stereo target to encourage alignment at one eye and imagines that his image is on near. The claw can be combined with near- the glass. (Indeed, most patients looking with far jump vergences, using the mirror in the one eye covered can image the reflection to distance and the claw at near. An esotrope be anywhere, either on or behind the glass.) can similarly use claw stereopsis by holding The patient then uncovers the eye, aligns it, his curled fist within his centration range and becomes aware of his reflection’s correct to compare one-eyed and two-eyed depth egocentric position behind the glass. Both perception. cover/uncover/recover and near-far jumps are continued a few minutes at a time over Yoked Prism Walk a number of sessions until the procedure is Yoked prisms are a powerful tool for building effortless. EDP. Mismatching eye and body information, yoked prisms often bypass habitual, automatic Claw Stereopsis patterns of perception and trigger exploration. In the movie Liar Liar, Jim Carry plays the The patient’s attention shifts to answer two part of a father who turns his fist into “a claw” questions: 1) “Where is my body compared to

232 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 the world?” (2) “Where is the world compared encouraging the patient to note how much of to my body?” Answering these questions the room he can see at one time, if things look can enhance both egocentric awareness and taller or shorter, if he feels taller or shorter, if simultaneous perception of peripheral space. things are consistently warped or unevenly This is true whether or not the patient is warped, some areas being constricted, some strabismic. Getzell has discussed the expansion being expanded. The patient might note how of the sphere of attention (although under a the room changes if he nods his head, how it different name) in non-strabismic patients.34 feels to walk, if he can simultaneously perceive Once the patient has learned to voluntarily the two sides of the room or simultaneously align his eyes, or align them enough to allow behold the floor and the ceiling. The therapist a peripheral fusion lock, the yoked prism encourages the patient to note anything that procedure is especially useful as a bridge to might extrovert him into the room and shift him egocentric awareness during natural seeing. into the egocentric system. Again the therapist The therapist positions the patient at the end of can ask if the length of the floor, simultaneously a room and has him look across the room and viewed, seems to be slanting up or down. describe what is seen. If the patient is in the The patient walks the length of the room central mode, he will likely mention windows, and back. The therapist then adjusts the yoked chairs, tables, cabinets, words on a poster, etc. prisms to base up. Now, if the patient is in If he is in the egocentric mode, he may say the egocentric system rather than the central something like “a long room” or “a big room.” system, when he looks to the end of the room Thus in the central, sequential mode, the and achieves gestalt awareness of the entire patient sees the particulars of the stuff in the length of the floor, the floor should appear to room. In the egocentric, simultaneous mode, slant downward. The patient’s walking to the the patient sees a room, with stuff in it, the stuff end of the room and back, and the questions all seen as one with its position in the room. directing attention are repeated. Once the patient has observed the room, With the patient again standing at the end he dons the 15-20 ^ yoked prism glasses base of the room, as at the beginning of the exercise, down. The therapist asks the patient to look to the therapist again removes the patient’s the end of the room and try to see the entire yoked prisms and asks the patient to examine length of the floor simultaneously—the patient the room and perceive if the room looks any is thus coached to develop gestalt awareness different. If necessary, the therapist can prompt of the floor the same way he previously the patient, “Does it seem as if you are seeing developed gestalt awareness of the projected the entire room at the same time? Most vectograph silver screen, or gestalt awareness patients will have shifted into the egocentric of the rectangular edge of the 3D television system to experience simultaneous perception screen, or gestalt awareness of the rectangular of the full room and will now be seeing, rather edge of the wall mirror. than individual things in the room, a room with Once the patient has simultaneous gestalt things in it, each thing having its individual awareness the full length of the floor, the position in the larger room. therapist asks whether the floor appears to be slanting upwards or downwards. If the patient Free Space Egocentric Stereopsis is in the egocentric mode, the floor will appear After the patient has used both vectographic to be slanting upwards. If the patient is in the and digital dichoptic images voluntarily to shift central mode, the floor may appear to be level or between central and egocentric seeing as floating downwards. In either case, the therapist described in previous sections of this paper, has the patient walk the length of the room, and after the patient has walked with the yoked

233 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 prism and experienced the perceptual shift into system, enter a hallway and instead of being egocentric seeing, the skill can be transferred to aware of all the space in the hallway are aware natural seeing. of the exit sign, or a particular doorway or wall While the patient is standing at one end of ornament. If instead, the patient shifts into the the room, the therapist stands half a dozen feet egocentric, simultaneous system, all the air in in front of the patient and has the patient direct the hallway becomes the center of simultaneous attention at the therapist’s nose, eyebrows, exploration; the patient should perceive the etc. to get the patient into the central mode. hallway in perspective, the dimensions of the Then the therapist asks the patient instead to hallway’s end appearing smaller in size than the be aware of the space in between the patient’s dimension of the walls, floor and ceiling directly nose and the therapist’s face and also to be surrounding the patient. aware of the rest of the room behind the To help with this perceptual shift, the therapist therapist. (Again, seeing space is not to be accompanies the patient down the hallway confused with calculating distance, comparing and encourages him to achieve simultaneous it to a picture of a ruler in the mind.) At this gestalt awareness of the full length of the floor, point in therapy, after the patient has already monitoring the patient’s eyes for telltale vertical experienced opening and closing the sphere of saccades that would signal that the patient is awareness, the patient should be aware of the looking at the nearer and farther parts of the shift of perspective, which comes when shifting floor for sequential processing rather than using into the where-is-it, egocentric, peripheral, and the peripheral/egocentric system. simultaneous system from the central, what is it, The therapist can encourage the patient to sequential system. The patient should now be perceive simultaneously the two walls of the aware of the whole room simultaneously, rather hallway and how they appear to flow backwards than just observing the details of the therapist’s as the therapist and patient walk. The therapist face. The patient, if asked, should be aware that can encourage the patient to see simultaneously the therapist has a position in the larger room. If the gestalt of the floor and ceiling. The hallway the therapist moves, the patient should be able can be used for the yoked base-up or base- to perceive that the therapist’s position in the down prism walks as the patient achieves gestalt room changes, being one third or one half the awareness of the air bounded by the length of way across the room. Again, if the patient’s eyes walls, floor and ceiling. The goal of this therapy are darting about the room, the therapist should is to remind the patient to have aligned eyes, remind the patient to look toward the therapist create peripheral awareness, and shift into the and to be simultaneously aware of the rest of EDP system whenever he enters a hallway. the room. The goal of the procedure is to enable a patient to, at any time, be able to think about the gestalt of space between his nose and any intermediate or distant object and to shift into the egocentric system. Once this becomes second nature, the patient can use egocentric awareness as a feedback for alignment.

Hallway Stereo Another tool for evoking egocentric awareness is a hallway. Patients who habitually limit perception to the central, sequential

234 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 Doorway Stereo alignment of eyes. Taking advantage of this, the In this activity the therapist serves as a central therapist and patient can take a walk outside, target framed by a doorway. The room behind the therapist coaching the patient to observe the therapist is visible beyond the doorway (see simultaneously the gestalt of the shape of the Figure 6). The therapist stands in front of the patches of blue sky and bordering objects door frame, facing the patient. First, the therapist and the subsequent improvement in the encourages the patient to constrict attention to relative stereopsis. The procedure is complete the individual features of the therapist’s face. if whenever the patient walks or drives, he Next, the therapist encourages the patient to experiences the joy of seeing the shape of the be aware of the distance between his nose and sky, extroverting attention, and enhancing EDP the therapist and to see how the wall behind the and alignment. doorway seems to spring back from the doorway as the room fills with space. Conclusion Another way to elicit this 3D perspective is Even without touching upon the newest uses to have the patient open up his side vision to of virtual reality,35 the digital age promises a achieve gestalt awareness of the door frame revolution in the nonsurgical care of strabismus. and to see how much space there is between But what is the goal of such treatment? Most the frame and the far wall in the room beyond would agree on “aligned eyes with clear, single the doorway. Again, the goal of the procedure is binocular vision.” The meanings of the “clear” to teach the patient to shift into the egocentric and “single” in the goal are fairly straightforward, system whenever he approaches a doorway. being almost universally considered in ophthalmic The awareness of space can then be used for care, even if only crudely approximated to check feedback concerning alignment. for neurological integrity. But what exactly does “binocular vision” mean? The Shape of the Sky Does binocularity mean that when we are A blue sky possesses a shape, sometimes placed in artificial conditions using dichoptic bounded merely by the horizon, sometimes images we all see the same illusions, perceptions chiseled at the edges by mountains, trees, that occur only in our minds rather than buildings, telephone poles, even launching accurately mirroring the world before us? Do we sites and Ferris wheels. Within, the patches of properly perceive first, second, and third degree blue sky are often divided by the fleecy white fusion, physiological diplopia, luster, or rivalry if of clouds or feathered wings of birds. Outside our eyes are fortuitously aligned with the targets, our office, for instance, in one direction the diplopia if they are not? Or is binocular vision trees cut a v-shaped patch of blue. In the other normal only if it allows us—without resorting to direction, the trees form a crooked blue figure sequential processing—to be instantly aware of of sky pierced by a white church steeple. When an object’s identity and position in space and to the therapist coaches the patient to use gestalt answer the questions “What is it?” and “Where awareness to behold the shape of the blue is it?” When we see an object in the room, are sky, the patient may shift into the egocentric we simultaneously aware of that object’s position system; the surrounding trees and telephone compared to the room and ourselves without poles may leap into perspective, each being the need to assemble the individual features of seen in its proper order of depth. the scene like pieces in a puzzle, one fixation at Thus the gestalt awareness needed to see a time? the shape of the sky affords the strabismic, or The gift of binocular vision is not necessarily other vision therapy patient, with yet another to be found in the numbers and the illusions but chance for appreciation of EDP to reward the in performance and the joy found in the visual

235 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 consciousness of Barry’s “palpable volume of language by past action, only then are we freed visual space,” and Vishwanath’s “characteristically to embrace the silent reality of space. Only then, vivid impression of tangible solid form, immersive do we truly begin to dance with the dimensions negative space and realness.” This paper has of the world. Today’s digital technologies, offered for the treatment of strabismus some added to breakthroughs in our understanding of procedures whose success supports Vishwanath’s egocentric depth perception, are making it ever theory of the role of egocentric awareness in the more possible for strabismic patients to see the perception of stereopsis. shape of the sky. EDP therapies—and there are many, many approaches, some described for nonstrabismic Conflicts of Interest visual anomalies by Getzell36—reward alignment The author has no financial interests in any with an awareness of threedimensional space of the products mentioned in this paper. while lessening the stress and discomfort of purely mechanical voluntary alignment. Acknowledgments Coaching heightened “gestalt,” “egocentric,” I’d like to thank my mentors Bill Ludlam, and “divided” attention extends the “sphere of Nathan Flax, Arnie Sherman, Martin Birnbaum, attention” to allow enhanced EDP and provide Elliot Forrest, and Irwin Suchoff. I’d also like to an escape from the perturbations of being thank Robert Sanet, Samantha Slotnick, and locked into a central identification system… Susan Barry for insights and inspiration. Finally, conceivably evolved to answer the question I would like to thank the Optometric Extension “Will it eat me?” Program Foundation for sponsoring my many In addition to building flexibility of mech­ strabismus seminars around the nation, allowing anical vergences, therapy should address me to learn from the questions of the hundreds the localization vergences inspired by EDP. of doctors and therapists who attended. Both vergence modes are helpful in achieving alignment and fusion. This paper has considered References one such treatment protocol available to augment 1. 1 Javal É. Manuel théorique et pratique du strabisme. the reader’s current treatment approach, Paris: Libraire De L’ Academie de Medecine, 1896. allowing strabismic and non-strabismic patients 2. Worth C. Squint: it’s causes, pathology, and treatment. alike to thrill at egocentric depth perception. London: John Bale, Sons & Danielsson, Ltd., 1903. When this perceptual shift occurs, it can 3. Brock FW. Pitfalls in orthoptic training of squints. Optom Weekly 1941: 32 (42):1185-1189. be dramatic, even profound. While the shapes 4. Brock FW. Conditioning the squinter to normal visual of objects often reduce to little more than habit. Optom Weekly 1941: 32 (28): 793-804. reflections of habitual sight, the shape of space 5. Flax N. A functional approach to strabismus. Transcript is always novel and, like creative visualization, San Jose Vision Training Seminar 1968, Aug 24-25: 36-37. invites a leap into liquid visual consciousness. 6. For an excellent summary of Brock’s contributions see Exploration and fresh, active seeing in the Barry SR. The work & wisdom of Dr. Fredrick W. Brock. Journal of Behavioral Optometry 2011: 22 (3): 59-63. moment replace habitual, automatic, stimulus- 7. Brock Fw. Brock technique of strabismus training response, stale perception carved by repetitive instruction manual. Keystone View Company. https://goo. action, often in a past too distant to recall. gl/lN6Gs0 In the words of philosopher Alva Noé, 8. Because this paper stresses the art rather than the “Consciousness is not something that happens science of strabismus treatment, I will use the essay form, employing the subjective first person rather than the to us. It is something we do or make. Better: it objective third person. is something we achieve. Consciousness is more 9. Levi DM, Knill DC, Bavelier D. Stereopsis and amblyopia: like dancing than it is like digestion.”37 When A mini-review. Vision Res 2015: 114 (9) 17-30. we escape the enchantment of details bound to

236 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016 10. Vishwanath D. Toward a new theory of stereopsis. 33. Morgan MW. The Maddox classification of vergence eye Psychological Review 2014: 121 (2) 153. movements. Am J of Optom & Physio Optics 1980: 57(9): 11. Barry SR. Fixing My Gaze: A Scientist’s Journey into Seeing 537-539. in Three Dimensions. New York: Basic Books, 2009:94. 34. Getzell has described a pervasive disorder that he calls, 12. Moses RA. Adler’s Physiology of the Eye, Fifth Edition. The “tunneling,” which he defines as “a form of exclusive C.V. Mosby Company, 1970: 672-682. concentration” whose treatment teaches patient’s to “hang on to space.” The current paper’s EDP would qualify 13. Slotnick, Samantha. Personal correspondence. as “hanging onto space,” and a constricted sphere of 14. Vishwanath D: 152. attention would qualify as tunneling—although “closeting” 15. Burian HM, von Noorden GK. Binocular Vision and Ocular would be closer to the truth. Getzell’s reflections helped Motility. Saint Louis: The C.V. Mosby Company, 1974:34. inform many of my own explorations into the treatment of strabismus. See Getzell JH. Tunneling—a pervasive vision 16. Vishwanath D: 151. disorder. Optom Vis Perf 2014: 2(1): 13-16. 17. Schor C. Perceptual-Motor Computational Model of 35. Our initial experience in using the Vivid Vision virtual Anomalous Binocular Correspondence. Optometry and reality technology in our clinic shows great promise for Visual Science 2015: 92(5): 544-550. expanding the sphere of attention. Although Vivid Vision 18. For a review of motor factors in binocular correspondence is being marketed primarily for the treatment ofamblyopia, see, Cook DL. Considering the ocular motor system in the its potential for strabismus therapy appears good, the treatment of anomalous retinal correspondence. J Am greatest handicap being that the patient’s objective eye Optom Assoc 1984: 55 (2): 109-117. position cannot be monitored during therapy. Still, the 19. Covariation is a change in correspondence which panoramic virtual world relieves the mismatch generally accompanies a change in strabismic angle. See Hallden found between dichoptic images and the surrounding U. Fusional Phenoma in Anomalous Correspondence. physical world. The technology’s greatest benefit, however, Uppsala, Almquist and wiksells Boktryckeria, 1952: 5-93. comes when the virtual reality headset is removed and patients find it easier to perceive EDP during the therapies 20. Quoted in Barry Sr. Ibid. detailed in the Natural Stereopsis section of this paper. 21. Brock FW. Visual training—Part III. Optom Weekly 1957: 48 Again, it is not just the instrument, but knowing how to (20): 977-982. bridge the gap into natural seeing that is important. See 22. Ludlam WM, in Borish IM (Ed). Clinical Refraction, 3rd ed. https://www.seevividly.com. Chicago: Professional Press, 1970: 1303-1304. 36. Getzell JH. Vision therapy procedures for tunneling. 23. Flax N. Ibid. Optom Vis Perf 2015: 3(4): 303-217. 24. Birnbaum MH. The role of the trainer in visual training. J 37. Noé A. Out of Our Heads: Why You Are Not Your Brain, Am Optom Assoc 1977: 48 (8): 1035-1039. and Other Lessons from the Biology of Consciousness. New York: Hill and Wang, 2009: xii. 25. Brock FW. Conditioning the squinter to normal visual habits. Optom Weekly 1941: 32 (28): 793-804. 26. Brock FW. Conditioning the squinter to normal visual AUTHOR BIOGRAPHY: habits. Optom Weekly 1941: 32 (29): 819-824. David Louis Cook, OD, FCOVD, FAAO 27. https://goo.gl/JUyzD1 Marietta, Georgia 28. Sunbeck D. Infinity walk. https://goo.gl/jRp7Y4 An Academy diplomate in binocular 29. https://goo.gl/IQIZDX vision and perception, Dr. Cook has 30. von Noorden GK, Compos EC. Binocular Vision and Ocular written on, treated, and lectured about Motility, Sixth Edition. Saint Louis: Mosby, Inc., 2002:298. strabismus for over 35 years. He is also the author of When Your Child Struggles, 31. Cook DL. Biomythology: the Skeptic’s Guide to Charles Visual Fitness, Biomythology, and the novel The Anatomy of Darwin and the Science of Persuasion. Bloomington, Blindness. IN:Authorhouse, 2016: 334-337. 32. Cook DL. Seeing is believing. Vision Dev & Rehab 2016: 2(2): 97-100.

237 Vision Development & Rehabilitation Volume 2, Issue 4 • December 2016