Stereopsis recovery, also recovery from stereoblindness, is the phenomenon of a stereoblind person gaining partial or full ability of stereo vision (stereopsis).
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 infancy and early childhood.See for example: 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."[...] The book's main contribution, however, is exposing the wrong-headed dogma that acuity and binocular vision can be restored only during a critical developmental period." —New England Journal of Medicine. (See introductory pages of: Susan R. Barry (2009) Fixing My Gaze.)"[...] Part memoir and part science, Fixing My Gaze is a fitting tribute to the determination of a patient and her optometrist in challenging conventional wisdom and dogma." —Journal of Behavioral Optometry. (See introductory pages of: Susan R. Barry (2009) Fixing My Gaze.)
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. The possible implications for the treatment of children with infantile esotropia 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 and strabismus surgery, may remove the double vision and recover the stereo vision which had temporarily been absent in the patient.
When children with congenital (infantile) strabismus (e.g. infantile esotropia) receive strabismus surgery at an early stage, this goes along with the hope that they may yet develop their full potential for binocular vision including stereopsis: A recent study concluded that quality of stereopsis and binocular vision may benefit from surgery being performed within six months of the onset of infantile esotropia, and this concerned both the amount of high-grade stereopsis achieved in some children and the overall percentage of children developing any stereopsis at all.
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 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, 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."Melvin L. Rubin, Lawrence A. Winograd: Taking Care of Your Eyes: A Collection of the Patient Information Handouts Used by America's Leading Eye Doctors, Triad Records (September 2002), 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 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 and vision therapy, or spontaneously after a stereoscopic 3D cinema experience, or subsequent to surgery in cases of horizontal comitant strabismus.
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 with diplopia, 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 with optometrist Theresa Ruggiero. Barry's case has been reported on by neurologist Oliver Sacks. Also David H. Hubel, winner of the 1981 Nobel Prize in Physiology or Medicine with Torsten Wiesel 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 when driving home after a vision therapy session with a Brock string.Susan R. Barry: Fixing My Gaze, Basic Books, 2009, . pp. 94–95.The sun was setting as I left Dr. Ruggerio's office after the long session with the Brock string. I got into my car, sat down in the driver's seat, placed the key in the ignition, and glanced at the steering wheel. It was an ordinary steering wheel against an ordinary dashboard, but it took on a whole new dimension that day. The steering wheel was floating in its own space, with a palpable volume of empty space between the wheel and the dashboard. […] I wondered if I as seen in stereoscopic depth but reminded myself that this should not be possible. […] The next morning I practiced the Broack string procedure for ten minutes before getting in the car […]. As I looked up to adjust the rearview mirror, the mirror popped out at me […]. Throughout the day, my stereo vision would emerge – intermittently, fleetingly, unexpectedly – bringing me moments of absolute wonder and delight.
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",. 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 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, 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, (abstract, full text ) whereas other studies have investigated the effects of eye training procedures. (full text ) Article 53
Post-surgical stereopsis