Stereopsis Recovery
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Stereopsis recovery, also recovery from stereoblindness, is the phenomenon of a
stereoblind Stereoblindness (also stereo blindness) is the inability to see in 3D using stereopsis, or stereo vision, resulting in an inability to perceive stereoscopic depth by combining and comparing images from the two eyes. Individuals with only one funct ...
person gaining partial or full ability of stereo vision (
stereopsis Stereopsis () is the component of depth perception retrieved through binocular vision. Stereopsis is not the only contributor to depth perception, but it is a major one. Binocular vision happens because each eye receives a different image becaus ...
). Recovering stereo vision as far as possible has long been established as an approach to the therapeutic treatment of stereoblind patients. Treatment aims to recover stereo vision in very young children, as well as in patients who had acquired but lost their ability for stereopsis due to a medical condition. In contrast, this aim has normally not been present in the treatment of those who missed out on learning stereopsis during their first few years of life. In fact, the acquisition of binocular and stereo vision was long thought to be impossible unless the person acquired this skill during a
critical period In developmental psychology and developmental biology, a critical period is a maturational stage in the lifespan of an organism during which the nervous system is especially sensitive to certain environmental stimuli. If, for some reason, the org ...
in infancy and early childhood. This hypothesis normally went unquestioned and has formed the basis for the therapeutic approaches to binocular disorders for decades. It has been put in doubt in recent years. In particular since studies on stereopsis recovery began to appear in scientific journals and it became publicly known that neuroscientist Susan R. Barry achieved stereopsis well into adulthood, that assumption is in retrospect considered to have held the status of a scientific
dogma Dogma is a belief or set of beliefs that is accepted by the members of a group without being questioned or doubted. It may be in the form of an official system of principles or doctrines of a religion, such as Roman Catholicism, Judaism, Islam ...
. Very recently, there has been a rise in scientific investigations into stereopsis recovery in adults and youths who have had no stereo vision before. While it has now been shown that an adult ''may'' gain stereopsis, it is currently not yet possible to predict how likely a stereoblind person is to do so, nor is there general agreement on the best therapeutic procedure. Also the possible implications for the treatment of children with
infantile esotropia Infantile esotropia is an ocular condition of early onset in which one or either eye turns inward. It is a specific sub-type of esotropia and has been a subject of much debate amongst ophthalmologists with regard to its naming, diagnostic feature ...
are still under study.


Clinical management of strabismus and stereoblindness

In cases of acquired strabismus with double vision (diplopia), it is long-established state of the art to aim at curing the double vision and at the same time recovering a patient's earlier ability for stereo vision. For example, a patient may have had full stereo vision but later had diplopia due to a medical condition, losing stereo vision. In this case, medical interventions, including
vision therapy Vision therapy (VT), or behavioral optometry, is an umbrella term for alternative medicine treatments using eye exercises, based around the pseudoscientific claim that vision problems are the true underlying cause of learning disabilities, parti ...
and
strabismus surgery Strabismus surgery (also: ''extraocular muscle surgery'', ''eye muscle surgery'', or ''eye alignment surgery'') is surgery on the extraocular muscles to correct strabismus, the misalignment of the eyes. Strabismus surgery is a one-day procedure ...
, may remove the double vision and recover the stereo vision which had temporarily been absent in the patient. Also when children with congenital (infantile) strabismus (e.g.
infantile esotropia Infantile esotropia is an ocular condition of early onset in which one or either eye turns inward. It is a specific sub-type of esotropia and has been a subject of much debate amongst ophthalmologists with regard to its naming, diagnostic feature ...
) receive strabismus surgery within the first few years or two of their life, this goes along with the hope that they may yet develop their full potential for
binocular vision In biology, binocular vision is a type of vision in which an animal has two eyes capable of facing the same direction to perceive a single three-dimensional image of its surroundings. Binocular vision does not typically refer to vision where an ...
including stereopsis. In contrast, in a case where a child's eyes are straightened surgically after the age of about five or six years and the child had no opportunity to develop stereo vision in early childhood, normally the clinical expectation is that this intervention will lead to cosmetic improvements but not to stereo vision. Conventionally, no follow-up for stereopsis was performed in such cases. For instance, one author summarized the accepted scientific view of the time with the words: "Stereopsis will never be obtained unless
amblyopia Amblyopia, also called lazy eye, is a disorder of sight in which the brain fails to fully process input from one eye and over time favors the other eye. It results in decreased vision in an eye that typically appears normal in other aspects. Amb ...
is treated, the eyes are aligned, and binocular fusion and function are achieved before the critical period for stereopsis ends. Clinical data suggest that this occurs before 24 months of age, but we do not know exactly when it occurs, because crucial pieces of basic science information are missing." For purposes of illustration, reference is made to a book of doctors' handouts for patients, written for the general public and published in 2002, which summarizes the limitations in the terms in which they, at the time, were fully accepted as medical state of the art as follows: "If an adult has a childhood strabismus that was never treated, it is too late to improve any amblyopia or
depth perception Depth perception is the ability to perceive distance to objects in the world using the visual system and visual perception. It is a major factor in perceiving the world in three dimensions. Depth perception happens primarily due to stereopsi ...
, so the goal may be simply cosmetic – to make the eyes appear to be properly aligned – though sometimes treatment does enlarge the extent of side vision." It has only been accepted very recently that the therapeutic approach was based on an unquestioned notion that has, since, been referred to as "myth" or "dogma". Recently, however, stereopsis recovery is known to have occurred in a number of adults. While this has in some cases occurred after visual exercises or spontaneous visual experiences, recently also the medical community's view of strabismus surgery has become more optimistic with regard to outcomes in terms of binocular function and possibly stereopsis. As one author states: :"The majority of adults will experience some improvement in binocular function after strabismus surgery even if the strabismus has been longstanding. Most commonly this takes the form of an expansion of binocular visual fields; however, some patients may also regain stereopsis." Scientific investigations on residual
neural plasticity Neuroplasticity, also known as neural plasticity, or brain plasticity, is the ability of neural networks in the brain to change through growth and reorganization. It is when the brain is rewired to function in some way that differs from how it p ...
in adulthood now also include studies on the recovery of stereopsis. Now it is a matter of active scientific investigation under which conditions and to which degree binocular fusion and stereo vision can be acquired in adulthood, especially if the person is not known to have had any preceding experience of stereo vision, and how outcomes may depend on the patient's history of therapeutic interventions.


Examples and case studies

Stereopsis recovery has been reported to have occurred in a few adults as a result of either medical treatments including
strabismus surgery Strabismus surgery (also: ''extraocular muscle surgery'', ''eye muscle surgery'', or ''eye alignment surgery'') is surgery on the extraocular muscles to correct strabismus, the misalignment of the eyes. Strabismus surgery is a one-day procedure ...
and
vision therapy Vision therapy (VT), or behavioral optometry, is an umbrella term for alternative medicine treatments using eye exercises, based around the pseudoscientific claim that vision problems are the true underlying cause of learning disabilities, parti ...
, or spontaneously after a stereoscopic
3D cinema 3D films are motion pictures made to give an illusion of three-dimensional solidity, usually with the help of special glasses worn by viewers. They have existed in some form since 1915, but had been largely relegated to a niche in the motion pict ...
experience.


Personal reports in ''Fixing my Gaze''

The most renowned case of regained stereopsis is that of neuroscientist Susan R. Barry, who had had alternating
infantile esotropia Infantile esotropia is an ocular condition of early onset in which one or either eye turns inward. It is a specific sub-type of esotropia and has been a subject of much debate amongst ophthalmologists with regard to its naming, diagnostic feature ...
with
diplopia Diplopia is the simultaneous perception of two images of a single object that may be displaced horizontally or vertically in relation to each other. Also called double vision, it is a loss of visual focus under regular conditions, and is often ...
, but no amblyopia, underwent three surgical corrections in childhood without achieving binocular vision at the time, and recovered from stereoblindness in adult age after
vision therapy Vision therapy (VT), or behavioral optometry, is an umbrella term for alternative medicine treatments using eye exercises, based around the pseudoscientific claim that vision problems are the true underlying cause of learning disabilities, parti ...
with optometrist Theresa Ruggiero. Barry's case has been reported on by neurologist
Oliver Sacks Oliver Wolf Sacks, (9 July 1933 – 30 August 2015) was a British neurologist, naturalist, historian of science, and writer. Born in Britain, Sacks received his medical degree in 1958 from The Queen's College, Oxford, before moving to the Uni ...
. Also David H. Hubel, winner of the 1981
Nobel Prize in Physiology or Medicine The Nobel Prize in Physiology or Medicine ( sv, Nobelpriset i fysiologi eller medicin) is awarded yearly by the Nobel Assembly at the Karolinska Institute, Nobel Assembly at the Karolinska Institute for outstanding discoveries in physiology or ...
with
Torsten Wiesel Torsten Nils Wiesel (born 3 June 1924) is a Swedish neurophysiologist. With David H. Hubel, he received the 1981 Nobel Prize in Physiology or Medicine, for their discoveries concerning information processing in the visual system; the prize was ...
for their discoveries concerning information processing in the visual system, commented positively on her case.. In 2009, Barry published a book ''Fixing My Gaze: A Scientist's Journey into Seeing in Three Dimensions'', reporting on her own and several other cases of stereopsis recovery. In her book ''Fixing my Gaze'', Susan Barry gives a detailed description of her surprise, elation and subsequent experiences when her stereo vision suddenly set in. Hubel wrote of her book: Her book includes reports of further persons who have had similar experiences with stereopsis recovery. Barry cites the personal experiences of several persons, including a man who was an artist and described his experience of seeing with stereopsis as "that he could see one hundred more times
negative space Negative space, in art, is the empty space around and between the subject(s) of an image. Negative space may be most evident when the space around a subject, not the subject itself, forms an interesting or artistically relevant shape, and s ...
", a woman who had been amblyopic before seeing in 3D described how empty space now "looks and feels palpable, tangible—alive!", a woman who had been strabismic since age two and saw in 3D after taking vision therapy and stated that "The coolest thing is the feeling you get being “in the dimension”", a woman who felt quite alarmed at the experience of suddenly seeing roadside trees and signs looming towards her, and two women who experienced an abrupt onset of stereo vision with a wide-angled view of the world, the first stating: "I was able to take in so much more of the room than I did before" and the second: "It was very dramatic as my
peripheral vision Peripheral vision, or ''indirect vision'', is vision as it occurs outside the point of fixation, i.e. away from the center of gaze or, when viewed at large angles, in (or out of) the "corner of one's eye". The vast majority of the area in the ...
suddenly filled in on both sides".. Common to Barry and at least one person on whom she had reported is the finding that also their mental representation of space changed after having acquired stereo vision: that even with one eye closed the feeling is to see "more" than seeing with one eye closed before recovering stereopsis.


Further cases in the media

Apart from Barry, another formerly stereoblind adult whose acquired ability for stereopsis has received media attention is neuroscientist Bruce Bridgeman, professor of psychology and psychobiology at
University of California Santa Cruz The University of California, Santa Cruz (UC Santa Cruz or UCSC) is a public land-grant research university in Santa Cruz, California. It is one of the ten campuses in the University of California system. Located on Monterey Bay, on the edge of ...
, who had grown up nearly stereoblind and acquired stereo vision spontaneously in 2012 at the age of 67, when watching the 3D movie '' Hugo'' with polarizing 3D glasses. The scene suddenly appeared to him in depth, and the ability to see the world in stereo stayed with him also after leaving the cinema.


Other first person accounts

Michael Thomas has described the experience of instantaneous onset of three dimensional vision at the age of 69 in a Public Facebook post.


Recent scientific investigations

There is a growing recent body of scientific literature on investigations into the recovery of stereopsis in adults which started to appear shortly before Oliver Sacks' ''The New Yorker'' publication drew public attention to Barry's discovery. A number of scientific publications have systematically assessed patients' post-surgical stereopsis,
abstractfull text
whereas other studies have investigated the effects of eye training procedures.
full text
Article 53


Post-surgical stereopsis

Certain conditions are known to be a prerequisite for stereo vision, for instance, that the amount of horizontal deviation, if any is present, needs to be small. In several studies it has been recognized that surgery to correct strabismus can have the effect of improving binocular function. One of these studies, published in 2003, explicitly concluded: "We found that improvement in binocularity, including stereopsis, can be obtained in a substantial portion of adults." That article was published together with a discussion of the results among peers in which the scientific and social implications of the medical treatment were addressed, for example concerning the long-term relevancy of stereopsis, the importance of avoiding diplopia, the necessity of predictable outcomes, and psychosocial and socioeconomic relevance. Among the investigations into post-surgical stereopsis is a publication of 2005 that reported on a total of 43 adults over 18 years of age who had surgical correction after having lived with from constant-horizontal strabismus for more than 10 years with no previous surgery or stereopsis, with visual acuity of 20/40 or more also in the deviating eye; in this group, stereopsis was present in 80% of exotropes and 31% of esotropes, with the recovery of stereopsis and stereoacuity being uncorrelated to the number of years the deviation had persisted. A study that was published 2006 included, aside an extensive review of investigations on stereopsis recovery of the last decades, a re-evaluation of all those patients who had had congenital or early-onset strabismus with a large constant horizontal divergence and had undergone strabismus surgery in the years 1997–1999 in a given clinic, excluding those who had a history of neurologic or systemic diseases or with organic retinal diseases. Among the resulting 36 subjects aged 6–30 years, many had regained binocular vision (56% according to an evaluation with Bagolini striated glasses, 39% with Titmus test, 33% with Worth 4-dot test, and 22% with Random dot E test) and 57% had stereoacuity of 200 sec of arc of better, leading to the conclusion that some degrees of stereopsis can be achieved even in cases of infantile or early-childhood strabism. Another study  found that some chronically strabismic adults with good vision could recover fusion and stereopsis by means of surgical alignment. In contrast, in a study in which a group of 17 adults and older children of at least 8 years of age, all of whom received strabismus surgery and post-operative evaluation after long-standing untreated
infantile esotropia Infantile esotropia is an ocular condition of early onset in which one or either eye turns inward. It is a specific sub-type of esotropia and has been a subject of much debate amongst ophthalmologists with regard to its naming, diagnostic feature ...
, most showed binocular fusion when tested with Bagolini lenses and an increased
visual field The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments". Or simply, visual field can be defined as the entire area that can be seen when an eye is fixed straight at a point ...
, but none demonstrated stereo fusion or stereopsis.
Stereoacuity Stereoscopic acuity, also stereoacuity, is the smallest detectable depth difference that can be seen in binocular vision. Specification and measurement Stereoacuity is most simply explained by considering one of its earliest test, a two-peg devic ...
is limited by the
visual acuity Visual acuity (VA) commonly refers to the clarity of vision, but technically rates an examinee's ability to recognize small details with precision. Visual acuity is dependent on optical and neural factors, i.e. (1) the sharpness of the retinal ...
of the eyes, and in particular by the visual acuity of the weaker eye. That is, the more a patient's vision of any one of the two eyes is degraded compared to the 20/20 vision standard, the lower are the prospects of improving or re-gaining stereo vision, unless visual acuity itself were improved by other means. Strabismus surgery itself does not improve visual acuity.


Stereopsis following training procedures

Orthoptic exercises have proven to be effective for reducing symptoms in patients with convergence insufficiency and decompensating exophoria by improving the near-point convergence of the eyes that is necessary for binocular fusion. Experiments on monkeys, published 2007, revealed improvements in stereoacuity in monkeys who, after having been raised with binocular deprivation through prisms for the first two years, were exposed to extensive psychophysical training. Their stereo vision recovered in part, but remained far more limited than that of normally raised monkeys. Scientists at the
University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant u ...
have stated that perceptual learning appears to play an important role. One investigation, published 2011, reported on a study on human stereopsis recovery using perceptual learning which was inspired by Barry's work. In this study, a small number of stereoblind subjects who had initially been stereoblind or stereoanomalous recovered stereopsis using perceptual learning exercises. Alongside the scientific assessment of the extent of recovery, also the subjective outcomes are described: "After achieving stereopsis, our observers reported that the depth “popped out,” which they found very helpful and joyful in their everyday life. The anisometropic observer GD noticed “a surge in depth” one day when shopping in a supermarket. While playing table tennis, she feels that she is able to track a ping-pong ball more accurately and therefore can play better. Strabismic observer AB is more confident now when walking down stairs because she can judge the depth of the steps better. Strabismics AB, DP, and LR, are able to enjoy 3D movies for the first time, and strabismic GJ finds it easier to catch a fly ball while playing baseball." In a follow-up study, the authors of this study pointed out that the stereopsis that was recovered following perceptual learning was more limited in resolution and precision compared to normal subjects' stereopsis. Dennis M. Levi was awarded the 2011 Charles F. Prentice Medal of the American Academy of Optometry for this work. There have been several attempts to make use of modern technology for enhanced binocular eye training, in particular for treating
amblyopia Amblyopia, also called lazy eye, is a disorder of sight in which the brain fails to fully process input from one eye and over time favors the other eye. It results in decreased vision in an eye that typically appears normal in other aspects. Amb ...
and interocular suppression. In some cases these modern techniques have improved patients' stereoacuity. Very early technology-enhanced vision therapy efforts have included the cheiroscope, which is a haploscope in which left- and or right-eye images can be blended into view over a drawing pad, and the subject may be given a task such as to reproduce a line image presented to one eye. However, historically these approaches were not developed much further and they were not put to widespread use. Recent systems are based on dichoptic presentation of the elements of a
video game Video games, also known as computer games, are electronic games that involves interaction with a user interface or input device such as a joystick, game controller, controller, computer keyboard, keyboard, or motion sensing device to gener ...
or
virtual reality Virtual reality (VR) is a simulated experience that employs pose tracking and 3D near-eye displays to give the user an immersive feel of a virtual world. Applications of virtual reality include entertainment (particularly video games), e ...
such that each eye receives different signals of the virtual world that the player's brain must combine in order to play successfully. One of the earliest systems of this kind has been proposed by a research group in the
University of Nottingham The University of Nottingham is a public university, public research university in Nottingham, United Kingdom. It was founded as University College Nottingham in 1881, and was granted a royal charter in 1948. The University of Nottingham belongs t ...
with the aim of treating amblyopia, using virtual reality masks or commercially available 3D shutter glasses. The group also has worked to develop perceptual learning training protocols that specifically target the deficit in stereo acuity to allow the recovery of normal stereo function even in adulthood. Another system of dichoptic presentation for binocular vision therapy has been proposed by researchers of the Research Institute of the
McGill University McGill University (french: link=no, Université McGill) is an English-language public research university located in Montreal, Quebec, Canada. Founded in 1821 by royal charter granted by King George IV,Frost, Stanley Brice. ''McGill Universit ...
Health Centre. Using a modified
puzzle video game Puzzle video games make up a broad genre of video games that emphasize puzzle solving. The types of puzzles can test problem-solving skills, including logic, pattern recognition, sequence solving, spatial recognition, and word completion. ...
''
Tetris ''Tetris'' (russian: link=no, Тетрис) is a puzzle video game created by Soviet Union, Soviet software engineer Alexey Pajitnov in 1984. It has been published by several companies for multiple platforms, most prominently during a dispute o ...
'', the interocular suppression of patients with amblyopia was successfully treated with dichotomic training in which certain parameters of the training material were systematically adapted during the course of four weeks. Clinical supervision of such procedures is required to ensure that double vision does not occur. Most of the patients who underwent this treatment gained improved visual acuity of the weaker eye, and some also showed increased stereoacuity. Another study performed at the same institute showed that dichoptic training can be more effective in adults than the more conventional amblyopia treatment of an
eye patch An eyepatch is a small patch that is worn in front of one eye. It may be a cloth patch attached around the head by an elastic band or by a string, an adhesive bandage, or a plastic device which is clipped to a pair of glasses. It is often worn ...
. For this investigation, 18 adults played the game Tetris for one hour each day, half of the group wearing eye patches and the other half playing a dichoptic version of the game. After two weeks, the group who played dichoptically showed a significant improvement of vision in the weaker eye and in stereopsis acuity; the eye patch group had moderate improvements, which increased substantially after they, too, were given the dichoptic training afterwards.Review of the Li et al (2013) article in: Dichoptic-based perceptual learning therapy, presented by means of a head-mounted display, is amenable also to amblyopic children, as it improves both the amblyopic eye's visual acuity and the stereo function. The researchers at McGill University have shown that one to three weeks of playing a dichoptic video game for one to two hours on a hand-held device "can improve acuity and restore binocular function, including stereopsis in adults". Furthermore, it has been suggested that these effect can be enhanced by anodal transcranial direct current stimulation (tDCS). Together with Levi of the University of California, Berkeley, scientists at the
University of Rochester The University of Rochester (U of R, UR, or U of Rochester) is a private university, private research university in Rochester, New York. The university grants Undergraduate education, undergraduate and graduate degrees, including Doctorate, do ...
have made further developments in terms of virtual reality computer games which have shown some promise in improving both monocular and
binocular vision In biology, binocular vision is a type of vision in which an animal has two eyes capable of facing the same direction to perceive a single three-dimensional image of its surroundings. Binocular vision does not typically refer to vision where an ...
in human subjects. Game developer James Blaha, who developed his own crowd-funded version of a dichoptic VR game for the
Oculus Rift Oculus Rift is a discontinued line of virtual reality headsets developed and manufactured by Oculus VR, a division of Meta Platforms, released on March 28, 2016. In 2012 Oculus initiated a Kickstarter campaign to fund the Rift's development, a ...
together with Manish Gupta and is continuing to experiment with the game, experienced stereopsis for the first time using his game. In 2011, two cases of adults with anisometropic amblyopia were reported whose visual acuity and stereoacuity improved due to learning-based therapies. There are indications that the suppression of binocularity in amblyopic subjects is due to a suppression mechanism that prevents the amblyopic brain from learning to see. It has been suggested that desuppression and neuroplasticity may be favored by specific conditions that are commonly associated with perceptual learning tasks and video game playing such as a heightened requirement of
attention Attention is the behavioral and cognitive process of selectively concentrating on a discrete aspect of information, whether considered subjective or objective, while ignoring other perceivable information. William James (1890) wrote that "Att ...
, a prospect of reward, a feeling of enjoyment and a sense of
flow Flow may refer to: Science and technology * Fluid flow, the motion of a gas or liquid * Flow (geomorphology), a type of mass wasting or slope movement in geomorphology * Flow (mathematics), a group action of the real numbers on a set * Flow (psych ...
.


Health care policy matters

Health insurances always review therapies in terms of clinical effectiveness in view of existing scientific literature, benefit, risk and cost. Even if individual cases of recovery exist, a treatment is only considered effective under this point of view if there is sufficient likelihood that it will predictably improve outcomes. In this context, medical coverage policy of the global health services organization
Cigna Cigna is an American multinational managed healthcare and insurance company based in Bloomfield, Connecticut. Its insurance subsidiaries are major providers of medical, dental, disability, life and accident insurance and related products and ser ...
"does not cover
vision therapy Vision therapy (VT), or behavioral optometry, is an umbrella term for alternative medicine treatments using eye exercises, based around the pseudoscientific claim that vision problems are the true underlying cause of learning disabilities, parti ...
,
optometric Optometry is a specialized health care profession that involves examining the eyes and related structures for defects or abnormalities. Optometrists are health care professionals who typically provide comprehensive primary eye care. In the Un ...
training Training is teaching, or developing in oneself or others, any skills and knowledge or fitness that relate to specific useful competencies. Training has specific goals of improving one's capability, capacity, productivity and performance. I ...
, eye exercises or
orthoptics Orthoptics is a profession allied to the eye care profession. Orthoptists are the experts in diagnosing and treating defects in eye movements and problems with how the eyes work together, called binocular vision. These can be caused by issues with ...
because they are considered experimental, investigational or unproven for any indication including the management of visual disorders and learning disabilities" based on a bibliographic review published by Cigna which concludes that "insufficient evidence exists in the published,
peer-reviewed Peer review is the evaluation of work by one or more people with similar competencies as the producers of the work ( peers). It functions as a form of self-regulation by qualified members of a profession within the relevant field. Peer revie ...
literature to conclude that vision therapy is effective for the treatment of any of the strabismic disorders except preoperative prism adaptation for acquired esotropia". Similarly, the U.S. managed health care company
Aetna Aetna Inc. () is an American managed health care company that sells traditional and consumer directed health care insurance and related services, such as medical, pharmaceutical, dental, behavioral health, long-term care, and disability plans ...
offers vision therapy only in contracts with supplemental coverage and limits its prescriptions to a number of conditions that are explicitly specified in a list of vision disorders.Clinical policy bulletins: Vision therapy
Number 0489, 4 June 2013, for review 13 June 2013 (downloaded 21 July 2013)


See also

* Recovery from blindness


References

{{DEFAULTSORT:Stereopsis recovery Neurophysiology Neuroscience Ophthalmology Stereoscopy Visual perception Visual system