Stereopsis recovery
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 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.
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.
"[6] 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.
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.
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.
[10] 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.
[2] 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: "It has been widely thought that an adult, cross-eyed since infancy, could never acquire stereovision, but to everyone's surprise, Barry succeeded.
A number of scientific publications have systematically assessed patients' post-surgical stereopsis,[21][22][23] whereas other studies have investigated the effects of eye training procedures.
[28][29] 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.
[22] Another study found that some chronically strabismic adults with good vision could recover fusion and stereopsis by means of surgical alignment.
Alongside the scientific assessment of the extent of recovery, also the subjective outcomes are described:[24]After achieving stereopsis, our observers reported that the depth "popped out", which they found very helpful and joyful in their everyday life.
One of the earliest systems of this kind has been proposed by a research group in the University of Nottingham with the aim of treating amblyopia, using virtual reality masks[37][38][39] or commercially available 3D shutter glasses.
[47] 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".
[45][46] 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, a prospect of reward, a feeling of enjoyment and a sense of flow.
[36][55][56] 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 "does not cover vision therapy, optometric training, eye exercises or orthoptics 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 literature to conclude that vision therapy is effective for the treatment of any of the strabismic disorders except preoperative prism adaptation for acquired esotropia".
