Archive for category Hemianopsia

[WEB SITE] Stroke Victims Look to Innovative Glasses to Improve Side Vision


CORONA, Calif.May 3, 2016 /PRNewswire/ — In addition to being the fourth leading cause of death in the United States, strokes can lead to any number of life-changing disabilities. One of the most common side effects of the estimated 800,000 strokes that occur each year in the country is a loss of side vision (hemianopsia) of up to one-half to the right or the left. With May being both “Stroke Prevention Month,” as well as “Healthy Vision Month,” there is a new focus on the challenges patients with stroke-related hemianopsia face, as well as the hope that advanced Side Vision Awareness Glasses (SVAG) can provide.

Logo – http://photos.prnewswire.com/prnh/20160502/362416LOGO

“When individuals experience hemianopsia much more than just their side vision is reduced,” says Richard Shuldiner, OD, founder of The International Academy of Low Vision Specialists (IALVS), “Their quality of life diminishes, too.”  So concerned about bumping into others or accidentally walking off a curb or into traffic, the condition can leave patients feeling insecure in unfamiliar surroundings. Some avoid going out altogether; others struggle to make it through the day. Though no treatment can actually restore the lost field of vision for these patients, Side Vision Awareness Glasses (SVAG) serve as optical field expansion devices that can increase patients’ viewing fields, improve their safety and enhance confidence.  So effective, patients with custom-made SVAG typically experience an increase of about 15 degrees in side vision awareness immediately upon putting them on. The use of SVAG may even allow some patients to resume driving.

Developed by IALVS member Dr. Errol Rummel, Director of the Neuro-optometric Rehabilitation Clinic at the Bacharach Institute for Rehabilitation in Pomona, NJ, SVAG represents an important advancement over other devices that came before them.  Crafted of lens materials known to minimize distortion, they are noticeably thinner. Also, there is no obvious line in front of the lens, no “thick button,” and no lens strip inserted through the front of the lens. The front of SVAG’s lenses is smooth and barely distinguishable from ordinary glasses.

More important than being better looking than previous devices designed to manage the condition, SVAG provides far-improved vision by offering the widest viewing area. Their vertical edge enables a person with hemianopsia to move their eyes just a few millimeters to access the SVAG area of the lens. Unlike devices that superimpose a narrow peripheral image over a person’s central vision, SVAG is easier for patients to use, as well as to learn to use. They’re also harder to break, because there is no glued seam splitting through the lens from front to back.

Patients with hemianopsia who are acutely aware of their side vision loss can often be trained to scan their eyes to compensate for their impairment, but for those who are unaware or inattentive to the condition, which doctors term “hemianopsia with neglect,” SVAG can go beyond increasing their field of vision—they can broaden their worlds.

In any case, a qualified low vision optometrist can help you determine whether Side Vision Awareness Glasses are right for you or a loved one.  All members of The International Academy of Low Vision Specialists are low vision optometrists with extensive training and experience in assisting patients suffering from stroke-related hemianopsia. To locate a member near you, simply visit their website: www.ialvs.com or call 1-888-778-2030.

For more information, contact:

Tracy LeRoux, The Link Agency, Inc.

(800) 291-0530

Email

SOURCE International Academy of Low Vision Specialists

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via Stroke Victims Look to Innovative Glasses to Improve Side Vision

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[ARTICLE] Segregation of Spontaneous and Training Induced Recovery from Visual Field Defects in Subacute Stroke Patients – Full Text

Whether rehabilitation after stroke profits from an early start is difficult to establish as the contributions of spontaneous recovery and treatment are difficult to tease apart. Here, we use a novel training design to dissociate these components for visual rehabilitation of subacute stroke patients with visual field defects such as hemianopia. Visual discrimination training was started within 6 weeks after stroke in 17 patients. Spontaneous and training-induced recoveries were distinguished by training one-half of the defect for 8 weeks, while monitoring spontaneous recovery in the other (control) half of the defect. Next, trained and control regions were swapped, and training continued for another 8 weeks. The same paradigm was also applied to seven chronic patients for whom spontaneous recovery can be excluded and changes in the control half of the defect point to a spillover effect of training. In both groups, field stability was assessed during a no-intervention period. Defect reduction was significantly greater in the trained part of the defect than in the simultaneously untrained part of the defect irrespective of training onset (p = 0.001). In subacute patients, training contributed about twice as much to their defect reduction as the spontaneous recovery. Goal Attainment Scores were significantly and positively correlated with the total defect reduction (p = 0.01), percentage increase reading speed was significantly and positively correlated with the defect reduction induced by training (epoch 1: p = 0.0044; epoch 2: p = 0.023). Visual training adds significantly to the spontaneous recovery of visual field defects, both during training in the early and the chronic stroke phase. However, field recovery as a result of training in this subacute phase was as large as in the chronic phase. This suggests that patients benefited primarily of early onset training by gaining access to a larger visual field sooner.

Introduction

Loss of up to one-half of the visual field (hemianopia) as result of post-chiasmatic stroke in one hemisphere occurs in about 30% of all stroke patients. Following a period of spontaneous recovery in the first 3–6 months (12), the patient enters the chronic phase of hemianopia.

Rehabilitation treatment most often involves eye movement training to compensate for the visual field defect (3) rather than visual restitution training, which reduces the defect itself. The latter has long been controversial (4). However, a recent series of investigations (512) have argued for the more balanced view that visual training of the defect may provide an additional and valuable approach to rehabilitation of occipital stroke patients.

Brain plasticity is believed to be greater in the acute stage after stroke when there is a window for relatively quick and extensive synaptic reorganization (13). Recommendations that rehabilitation should begin “as soon as possible” or “early” are therefore common in clinical guidelines (1415). However, many of these recommendations are based on limited data (16), and there are no agreed definitions of what constitutes early rehabilitation (17). Thus far, visual restitution training is generally applied in the chronic phase after stroke, so that spontaneous recovery can be excluded, and changes in the visual field can be attributed to training. In this way, one can obtain an accurate estimate of the effect of the training itself (811). Yet, we wondered if visual restitution training would profit from an early start as suggested in the rehabilitation literature.

The effect of visual perceptual learning in normally sighted subjects is often restricted to the trained region of the visual field (1820) and specific to the trained task (2122). This raises the question whether the visual recovery that is induced by visual restitution training is also limited to just the trained region and task. Several studies have shown that recovered vision after restitution training transfers to untrained visual tasks (1011) but only to a limited extent to untrained regions. For example, the defect reduction induced by training of the intact visual hemifield was significantly smaller than the reduction induced by training the affected hemifield itself, and it was not significantly different from the defect reduction following a non-intervention period (11). Because spontaneous recovery could be excluded in that study, any improvement during intact training could point to a spillover effect of training between the two hemispheres. That is, the defect reduces—albeit to limited extent—even when another part of the visual field is trained.

Following the practice of general rehabilitation medicine, one would preferably train patients in the early phase of stroke. To do so, we applied a method that builds on the observation that visual training carries over to neighboring areas only to a limited extent. That is, we used two training rounds, which targeted complementary parts of the defect [regions of interest (ROIs)], while monitoring in both training rounds the trained and the untrained half of the defect. The untrained half of the defect, which serves as an internal control for the trained half, will show spontaneous recovery and a potential spillover from the neighboring trained region. To assess that spill over, we used data from seven patients who were trained in the chronic phase of stroke using the same method. The differences between the defect reductions for the subacute phase of stroke and the chronic phase of stroke in the trained and untrained parts of the defect should allow us to distinguish between spillover, spontaneous recovery and training-induced recovery. This allows us to test the hypothesis that training in the early phase leads to a larger defect reduction than training in the chronic phase.

Materials and Methods

The study was approved by the ethical committee CMO Arnhem–Nijmegen in correspondence with the 1964 Declaration of Helsinki.

20 Subacute stroke patients and 10 chronic stroke patients with visual field defects due to post-geniculate damage were included following written informed consent. Subacute stroke patients were screened for participation in four neurology departments of Dutch hospitals: UMC in Utrecht, St. Elisabeth Hospital in Tilburg, CWZ in Nijmegen and St. Antonius Hospital in Nieuwegein (screening; eight patients). Patients could also sign up for the study by filling out a form on our website (www.hemianopsie.nl; 12 patients), to be screened at a regional office by the first author. Chronic stroke patients all applied through the website.

Patients inclusion criteria as follows:

∗ age between 18 and 75 years;

∗ presence of homonymous visual field defect.

Patient exclusion criteria as follows:

∗ visual neglect (as assessed by line bisection test);

∗ cardiac or other implants (for the chronic patients only: MRI scans were made; to be presented elsewhere).

The intake procedure included a Goldmann perimetry measurement. Patient demographics can be found in Table S2 in Supplementary Material.

For the 30 included patients, we had to exclude the data of 3 subacute and 3 chronic patients from further analysis. In the three subacute patients, the training was not applied as intended because the defect was not divided in two equal halves (n = 2), or for unequal duration of the training rounds (n = 1). In the chronic patients, absence of an absolute defect (n = 1), inability to cope with training demands (n = 1), and anxiety for fMRI scanner measurements (n = 1) were reasons to exclude their data. Thus, in total, we analyzed 17 subacute and 7 chronic data sets.

The 20 subacute patients were trained by DB for this study, the 10 chronic patients were trained by JE in a parallel study using the same training paradigm.

Study Design

Before the training, baseline values were established for visual field size (Goldmann perimetry), reading speed and Goal Attainment Scaling (GAS: personally customized and realistic goals).

Following these baseline measurements, the visual field defect was divided in equal halves using the following procedure. First, meridional angles through the defect were established that were farthest apart. Then, the average of these two outer meridional angles formed the border between the two training regions (in the case of SA15, the division was along the vertical midline). One-half of the visual field defect was trained for 8 weeks, while the other half was untrained. After this period, intermediate measurements were carried out (perimetry and reading speed tests) during the course of one week. Then, a second training period of 8 weeks was started, in which the training was applied to the other half of the defect, while the first half received no further training. Post-measurements were carried out as during baseline measurements (Figure 1). Finally, we collected follow-up perimetry data in the subacute group. The period without training, in-between the final training session and the follow-up perimetry of the subacute group, is denominated “No Intervention.”

Figure 1. Study design and time line for subacute patients. The defect was divided into two training regions [region of interest (ROI) 1, ROI 2] of equal size. In this example, the left upper quarter field was trained first, followed by the lower left quadrant. This order was randomized between patients. For chronic patients, the study design was similar, except that the first training started at least 10 months after the stroke (and about 2 months after intake), and no follow-up measurements were taken.

Continue —>  Frontiers | Segregation of Spontaneous and Training Induced Recovery from Visual Field Defects in Subacute Stroke Patients | Neurology

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[ARTICLE] Audiovisual Rehabilitation in Hemianopia: A Model-Based Theoretical Investigation – Full Text

Hemianopic patients exhibit visual detection improvement in the blind field when audiovisual stimuli are given in spatiotemporally coincidence. Beyond this “online” multisensory improvement, there is evidence of long-lasting, “offline” effects induced by audiovisual training: patients show improved visual detection and orientation after they were trained to detect and saccade toward visual targets given in spatiotemporal proximity with auditory stimuli. These effects are ascribed to the Superior Colliculus (SC), which is spared in these patients and plays a pivotal role in audiovisual integration and oculomotor behavior. Recently, we developed a neural network model of audiovisual cortico-collicular loops, including interconnected areas representing the retina, striate and extrastriate visual cortices, auditory cortex, and SC. The network simulated unilateral V1 lesion with possible spared tissue and reproduced “online” effects. Here, we extend the previous network to shed light on circuits, plastic mechanisms, and synaptic reorganization that can mediate the training effects and functionally implement visual rehabilitation. The network is enriched by the oculomotor SC-brainstem route, and Hebbian mechanisms of synaptic plasticity, and is used to test different training paradigms (audiovisual/visual stimulation in eye-movements/fixed-eyes condition) on simulated patients. Results predict different training effects and associate them to synaptic changes in specific circuits. Thanks to the SC multisensory enhancement, the audiovisual training is able to effectively strengthen the retina-SC route, which in turn can foster reinforcement of the SC-brainstem route (this occurs only in eye-movements condition) and reinforcement of the SC-extrastriate route (this occurs in presence of survived V1 tissue, regardless of eye condition). The retina-SC-brainstem circuit may mediate compensatory effects: the model assumes that reinforcement of this circuit can translate visual stimuli into short-latency saccades, possibly moving the stimuli into visual detection regions. The retina-SC-extrastriate circuit is related to restitutive effects: visual stimuli can directly elicit visual detection with no need for eye movements. Model predictions and assumptions are critically discussed in view of existing behavioral and neurophysiological data, forecasting that other oculomotor compensatory mechanisms, beyond short-latency saccades, are likely involved, and stimulating future experimental and theoretical investigations.

Introduction

The primary human visual pathway conveys the majority of retinal fibers to the lateral geniculate nucleus of the thalamus and then, via the optic radiations, to the primary visual cortex (V1) (the retino-geniculo-striate pathway). V1 is the main distributor of visual information to extrastriate visual areas, for further processing. A secondary visual pathway (the retino-collicular pathway) routes a minority of retinal fibers directly to the Superior Colliculus (a midbrain structure), which also has reciprocal connections with striate and extrastriate visual cortices (May, 2006).

Patients with lateralized damages to the primary visual cortex (V1) or to the neural pathway feeding V1 often develop homonymous hemianopia, a visual field defect with the loss of conscious vision in one hemifield. Hemianopic patients cannot perceive visual stimuli presented in the blind hemifield; moreover, they show the inability to spontaneously develop effective oculomotor strategies to compensate for the visual field loss (Hildebrandt et al., 1999Zihl, 2000Tant et al., 2002).

Despite the visual deficit, hemianopic patients can preserve the ability to integrate audiovisual stimuli in the affected field, with beneficial effects (Frassinetti et al., 2005Leo et al., 2008). In particular, data by Frassinetti and colleagues (Frassinetti et al., 2005) show that patients performing a visual detection task, while maintaining central fixation, significantly improved conscious visual detections in the affected field, when the auditory stimuli were applied in spatial and temporal coincidence with the visual targets.

The Superior Colliculus is the most likely structure mediating this multisensory improvement, because of its anatomical connections and the properties of its neuronal responses. Indeed, SC neurons receive not only visual information but also signals from other different sensory modalities, such as audition (Meredith and Stein, 1986Stein and Meredith, 1993May, 2006). Visual and auditory information are integrated in multisensory SC neurons according to specific principles (Stein and Meredith, 1993): an audiovisual stimulation elicits a stronger neuronal activation than each single component, when the visual and auditory components are presented in spatial and temporal register (spatial and temporal principle). Moreover, a proportionally greater enhancement of multisensory neuronal activation is evoked when weakly effective unisensory stimuli are combined, compared to the combination of highly effective stimuli (inverse effectiveness principle). The SC integrative principles have strong implications in hemianopia, as the SC and the retino-collicular pathway are preserved in these patients. Visual retinal input to SC, although weak, can still be efficiently combined with an accessory auditory input thanks to the inverse effectiveness principle, provided the rule of spatial and temporal proximity is satisfied. Furthermore, SC multisensory enhancement can affect cortical visual processing thanks to the projections from the SC to the visual cortices.

In addition to the immediate, “online” multisensory improvement in visual detection, there is also evidence of prolonged, “offline” effects that can be induced by repeated exposure to audiovisual stimuli. Indeed, long-lasting improvements of visual performances in hemianopic patients, promoted by audiovisual training protocols stimulating the blind hemifield, have been reported (Bolognini et al., 2005Passamonti et al., 2009Dundon et al., 2015bTinelli et al., 2015Grasso et al., 2016). During the training, a visual target was given in close spatial and temporal proximity with an auditory stimulus, at various positions in the visual field; patients were asked to detect the presence of the visual target, by directing the gaze toward it from a central fixation point. Results revealed a significant post-training improvement in detection of unimodal visual targets in the blind field when the patients were allowed to use eye movements, while a weak amelioration was found when they had to maintain central fixation (Bolognini et al., 2005Tinelli et al., 2015). Such results suggest that the audiovisual training could promote an increased oculomotor response to visual stimuli in the affected hemifield.

Beyond the “online” effects of audiovisual stimulation, the Superior Colliculus is a possible candidate for mediating the training effects, too. Indeed, the SC projects to brainstem motor areas controlling eyes and head orientation, and is critically involved in the initiation and execution of reflexive (i.e., exogenously-driven) saccades (Sparks, 1986Jay and Sparks, 1987aMay, 2006Johnston and Everling, 2008). Importantly, more than 70% of SC neurons projecting to the brainstem and, therefore involved in saccade generation, respond to multisensory stimulations (Meredith and Stein, 1986). As such, audiovisual stimuli, enhancing multisensory SC activation, might plastically reinforce the gain of the transduction from the SC sensory response to the motor output; in other words, after training the oculomotor system could have acquired increased responsiveness to the visual input conveyed via the retino-collicular pathway. However, the plastic mechanisms and synaptic reorganization that can functionally instantiate these visuomotor capabilities remain undetermined. Moreover, it is unclear whether the training may even stimulate genuine visual restitution beyond oculomotor compensation, and how the compensatory and restitutive effects may complementary contribute to visual improvements.

Recently, we have developed a neural network model (Magosso et al., 2016) that formalized the main cortico-collicular loops involved in audiovisual integration, and implemented—via neural connections and input-output neural characteristics—the SC multisensory integrative principles. The network postulated neural correlates of visual consciousness and mimicked unilateral V1 lesion. Simulations, performed in fixed-eyes condition, reproduced the “online” effects of enhanced visual detection under audiovisual stimulation.

Here, we extend our previous neural network to explore the effects of training in simulated hemianopic patients, providing quantitative predictions that can contribute to a mechanistic understanding of visual performance improvement observed in real patients. To this aim, the network has been integrated by novel elements. First, we have included a module of saccade generation, embracing the colliculus sensory-motor transduction; in this way, we can account for the potentiality of short-latency saccades triggered in a bottom-up fashion. Second, Hebbian mechanisms of synaptic learning have been implemented and adopted during training simulations. Different training paradigms (audiovisual multisensory/visual unisensory stimulation in eye-movements/fixed-eyes condition) are tested, to examine their efficacy in promoting different forms of rehabilitation (compensatory/restitutive), and to assess the predicted results in light of in vivo data.

 

Materials and Methods

The neural network is conceptually made up of two modules (Figure 1A). A sensory module (blue blocks and lines) includes cortical and subcortical (SC) neuronal areas devoted to the sensory representation of the external stimulation. An oculomotor module (red blocks and lines) can potentially react to the sensory neural representation, generating a saccade toward the external stimulation. The SC is involved in both modules.

Figure 1. (A) Sketch of the neural network architecture. Blue blocks and lines represent the sensory module; red blocks and lines denote the oculomotor module. R, retina; V1, primary visual cortex; E, extrastriate visual cortex; SC, Superior Colliculus; A, auditory area; FP, saccade-related frontoparietal areas (δ denotes a pure delay); SG, Brainstem Saccade Generator. g(t) is the current gaze position (resulting from the oculomotor module); θg is the target gaze position decoded from the SC activity. pis the position of the external (visual or spatially coincident audiovisual) stimulus in head-centered coordinates, and p-g(t) is the stimulus position in retinotopic coordinates. WH, Q denotes inter-area synapses from neurons in area Q to neurons in area H(B) Exemplary pattern of basal (i.e., pre-training) inter-area synapses. Here, synapses WSC, R from the retina to SC are depicted, limited to about one hemifield (−10° ÷ +90°) (the same pattern holds for the remaining not shown positions). x-axis reports the position (j, in deg) of the pre-synaptic neuron in area R and the y-axis the position (i, in deg) of the post-synaptic neuron in area SC. The color at each intersection (j, i) codes the strength of the synapse from the pre-synaptic neuron j in area R to the post-synaptic neuron i in SC. Similar patterns hold for all other inter-area synapses within the sensory module. Consistently with the following figures, scale color is between 0 and the maximum value reachable by training (WSC,RmaxWmaxSC,R). WSC,R0W0SC,R denotes the central weight of the pre-training Gaussian pattern of the synapses. (C) Schematic picture of the eye-centered topological organization of neurons in each area. In case (1), the stimulus induces an activation bubble centered on the neuron with preferred retinal position = 45°, in a given area; in case (2), the stimulus induces an activation bubble centered on the neuron with preferred retinal position = 45°–30° = 15°.

Continue —> Frontiers | Audiovisual Rehabilitation in Hemianopia: A Model-Based Theoretical Investigation | Frontiers in Computational Neuroscience

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[VIDEO] How to Biology & Anatomy: Optic pathways, visual fields and the lesions – YouTube

 

See the original video here: http://www.showme.com/sh/?h=xyvD3Gi Created by Dale Ledford, a college Biology, Human Anatomy, and Physiology instructor in Blountville, Tennessee.

via How to Biology & Anatomy: Optic pathways, visual fields and the lesions – YouTube

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[VIDEO] Homonymous Hemianopia – YouTube

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[Educational] VISUAL DISTURBANCES IN NEUROLOGICAL CONDITIONS: ASSESSMENT AND TREATMENT

 

The purpose of this education is to help you understand how to screen, refer and treat patients related to functional performance.
WE DO NOT DIAGNOSE!

Objectives for Today
■ Identify signs and symptoms that indicate a potential vision problem.
■ Identify the differences amongst the variety of vision problems that can occur
following a neurological event and how it impacts functional performance with
ADL/IADLs.
■ Identify how to accurately screen for potential vision problems and when to refer to
an eye specialist.
■ Identify therapeutic approaches used to treat and compensate for problems,
allowing for improved function.

Full Text PDF (79 pages)

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[ARTICLE] Development and Implementation of a New Telerehabilitation System for Audiovisual Stimulation Training in Hemianopia – Full Text

Telerehabilitation, defined as the method by which communication technologies are used to provide remote rehabilitation, although still underused, could be as efficient and effective as the conventional clinical rehabilitation practices. In the literature, there are descriptions of the use of telerehabilitation in adult patients with various diseases, whereas it is seldom used in clinical practice with child and adolescent patients. We have developed a new audiovisual telerehabilitation (AVT) system, based on the multisensory capabilities of the human brain, to provide a new tool for adults and children with visual field defects in order to improve ocular movements toward the blind hemifield. The apparatus consists of a semicircular structure in which visual and acoustic stimuli are positioned. A camera is integrated into the mechanical structure in the center of the panel to control eye and head movements. Patients can use this training system with a customized software on a tablet. From hospital, the therapist has complete control over the training process, and the results of the training sessions are automatically available within a few minutes on the hospital website. In this paper, we report the AVT system protocol and the preliminary results on its use by three adult patients. All three showed improvements in visual detection abilities with long-term effects. In the future, we will test this apparatus with children and their families. Since interventions for impairments in the visual field have a substantial cost for individuals and for the welfare system, we expect that our research could have a profound socio-economic impact avoiding prolonged and intensive hospital stays.

Introduction

Telerehabilitation, defined as the method by which communication technologies are used to provide remote rehabilitation, although still underused, could be as efficient and effective as the conventional clinical rehabilitation practices (1). In the literature, we can find some descriptions of the use of telerehabilitation in adult patients for various types of disorder, whereas it is seldom used in clinical practice with children and adolescents (2).

The development and use of telerehabilitation program are slow because they are affected by many logistical factors, such as regional economic resources, medical technical support systems, and population quality, but their potential is very high, as they are conceived and studied to improve patients’ ability to perform activities from daily life, thereby increasing their independence (3). For example, for adult post-stroke patients, telerehabilitation is widely used with the main goal of giving disabled people the same quality of motor, cognitive, and neuropsychological rehabilitation at home as they would have in-home visit and day-care rehabilitation (457).

So far, the application of telerehabilitation during childhood has been primarily limited to preterm babies (8) and children with hemiplegia (910), with autism spectrum disorders (11), with speech and language disorders (1213), and with learning difficulties (1416). Despite the well-known impact of visual defects on cognitive functioning and neurological recovery (17), no study has yet investigated the application of telerehabilitation with children with visual impairments.

Here, we describe an innovative telerehabilitation platform, which consists in an audiovisual telerehabilitation (AVT) system, developed for children and adults with visual field defects caused by post-chiasmatic brain lesions. The AVT system allows patients to exercise independently, in an intensive, active, and functional way and in a familiar environment, under remote supervision; it consists of a mobile device platform with remote control, which is accessible directly from home and suitable both for adults, adolescents, and children from the age of 8.

The AVT system is based on a very promising multisensory audiovisual therapy, originally developed for the treatment of adults and children with visual field defects caused by brain lesions (1819). Basically, this training aims to stimulate multisensory integration mechanisms in order to reinforce visual and spatial compensatory functions (i.e., implementation of oculomotor strategies). In this first phase of the study, we tested the feasibility and efficacy of AVT in three adult patients with chronic visual field defects, in order to explore how the apparatus can be implemented at home.[…]

Continue —>  Frontiers | Development and Implementation of a New Telerehabilitation System for Audiovisual Stimulation Training in Hemianopia | Neurology

Figure 1. Magnetic resonance imaging of the brain and visual field campimetry of S1, S2, and S3.

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[ARTICLE] Driving with Hemianopia V: Do Individuals with Hemianopia Spontaneously Adapt Their Gaze Scanning to Differing Hazard Detection Demands?

Abstract

Purpose: We investigated whether people with homonymous hemianopia (HH) were able to spontaneously (without training or instructions) adapt their blind-side scan magnitudes in response to differing scanning requirements for detection of pedestrians in a driving simulator when differing cues about pedestrian eccentricities and movement behaviors were available in the seeing hemifield.

Methods: Twelve HH participants completed two sessions in a driving simulator pressing the horn when they detected a pedestrian. Stationary pedestrians outside the driving lane were presented in one session and approaching pedestrians on a collision course in the other. Gaze data were analyzed for pedestrians initially appearing at approximately 14° in the blind hemifield. No instructions were given regarding scanning.

Results: After appearing, the stationary pedestrians’ eccentricity increased rapidly to a median of 31° after 2.5 seconds, requiring increasingly larger blind-side gaze scans for detection, while the approaching pedestrians’ eccentricity remained constant at approximately 14°, requiring a more moderate scan (∼14°) for detection. Although median scan magnitudes did not differ between the two conditions (approaching: 14° [IQR 9°–15°]; stationary: 13° [IQR 9°–20°]; P= 0.43), three participants showed evidence of adapting (increasing) their blind-side scan magnitudes in the stationary condition.

Conclusions: Three participants (25%) appeared to be able to apply voluntary cognitive control to modify their blind-side gaze scanning in response to the differing scanning requirements of the two conditions without explicit training.

Translational Relevance: Our results suggest that only a minority of people with hemianopia are likely to be able to spontaneously adapt their blind-side scanning in response to rapidly changing and unpredictable situations in on-road driving.

 

Introduction
Homonymous hemianopia (HH) is the loss of half the field of vision on the same side in both eyes. It is caused by lesions in the postchiasmal visual pathways, primarily due to strokes and, to a lesser extent, trauma and tumors.1 People with HH may compensate for their hemifield loss by scanning using eye and/or head movements toward the blind hemifield. However, there is accumulating evidence2 that many do not compensate well leading to impaired hazard detection in simulated driving,38 in on-road driving,9 and in walking tasks.10
In order to see an object in the blind hemifield, people with complete HH need to scan at least as far into the blind hemifield as the location of the object. However, they receive no visual cues from peripheral vision as to when to scan or how far to scan into the blind hemifield. People with HH are usually aware of their visual field loss (unless they have spatial neglect) and could use voluntary, cognitive control to guide their blind-side scanning. For example, patients with HH may be trained or told to scan to the blind side in order to detect potential hazards.11 However, relatively little is known about the extent to which people with HH use such strategies in real world situations (e.g., driving2) or whether they are able to adapt their scanning patterns in response to differing conditions (e.g., a busy city-center street with frequent hazards versus a quiet rural road with infrequent hazards).
Only a limited number of studies have addressed the question of whether people with HH adapt their scanning strategies. A recent study using a gaze-contingent simulation of HH concluded that efficient search strategies were not spontaneously adopted by the majority of participants; however, a minority (4/20) did modify their search strategy in response to changing task demands. In general, a strategy of searching the seeing side before the blind side was adopted both for difficult search tasks in which each item needed to be viewed in a serial fashion as well as easier tasks in which the target was clearly visible in the periphery and a large saccade toward the blind side would have been the more efficient strategy. Only four participants modified their search to start from the blind field when the task was easy. In another study, Schuett et al.12reported that normally sighted participants with simulated HH became more efficient at a dot-counting task (an irregular array of dots) and a reading task after a short period of practice (∼15 minutes) on each of the tasks. However, in follow-up studies they found no evidence of transfer of learning (modification of gaze behaviors) between the two tasks, either for simulated HH13 or real HH13 (i.e., participants who practiced the dot-couting task did not demonstrate improvements on the reading task and vice versa).
In a study involving detection of peripherally presented moving basketballs within a virtual environment, participants with HH scanned less extensively in the horizontal plane and spent more time looking toward the ground when performing the task while walking than when seated.10 Thus, when walking, it appears that they modified their gaze behaviors in favor of walking, at the expense of peripheral target detection. In a driving simulator study3 involving detection of stationary pedestrians on the blind and seeing sides, no improvement in blind-side detection rates was found between two simulator sessions, approximately 1 week apart. These results suggested that no learning had occurred, despite 60 minutes of test drives at each session. Moreover, information was available in the seeing hemifield about pedestrian eccentricity, which could have been used as a guide for the scanning behaviors that were needed for detection of blind-side pedestrians. However, gaze movements were not recorded so it was unknown whether there were any changes in gaze behaviors.
In this paper, we report an analysis of gaze behaviors from a driving simulator study5 in which we evaluated detection performance of people with HH for pedestrians that were stationary to the side of the driving lane and pedestrians that approached the driving lane, walking or running on a collision course (detection rates and reaction time results were reported previously5). The scanning requirements for successful detection of blind-side pedestrians differed for the two pedestrian conditions, providing an opportunity to examine whether participants adapted their scanning behaviors. In the stationary condition the pedestrians did not move after appearing.3,5 Thus, their eccentricity increased rapidly as the car progressed, moving them farther into the blind hemifield, requiring increasingly larger gaze movements for detection. On the other hand, in the approaching condition, the pedestrians were on a collision course,5,14 so their eccentricity remained approximately constant as the car progressed. Thus, the magnitude of the gaze scan needed for detection would also have remained approximately constant, and smaller than the gaze scan needed in the stationary condition.
Herein, we address two main questions: (1) did participants with HH adapt their blind-side scan magnitudes (without training or instructions) to match the differing scanning requirements (pedestrian eccentricities) for successful blind-side detection in the stationary and approaching conditions; and (2) were the previously reported5 differences in blind-side detection rates between the two conditions accounted for by differences in the scanning requirements? We quantified the magnitudes of scans after the appearance of pedestrians in the blind hemifield and tested the hypothesis that blind-side scans would be larger in the stationary than the approaching condition. We expected to find greater evidence of within-session learning in the stationary condition (where scanning requirements were higher) than in the approaching condition. In addition, we tested the hypothesis that more time would be available after the pedestrian appearance for a moderate-sized gaze scan to reach the pedestrian in the approaching than the stationary condition, resulting in better detection rates but longer response times.[…]

Continue —> Driving with Hemianopia V: Do Individuals with Hemianopia Spontaneously Adapt Their Gaze Scanning to Differing Hazard Detection Demands? | TVST | ARVO Journals

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[ARTICLE] Visually evoked responses from the blind field of hemianopic patients – Full Text

Abstract

Hemianopia is a visual field defect characterized by decreased vision or blindness in the contralesional visual field of both eyes. The presence of well documented above-chance unconscious behavioural responses to visual stimuli presented to the blind hemifield (blindsight) has stimulated a great deal of research on the neural basis of this important phenomenon. The present study is concerned with electrophysiological responses from the blind field. Since previous studies found that transient Visual Evoked Potentials(VEPs) are not entirely suitable for this purpose here we propose to use Steady-State VEPs (SSVEPs). A positive result would have important implications for the understanding of the neural bases of conscious vision. We carried out a passive SSVEP stimulation with healthy participants and hemianopic patients. Stimuli consisted of four black-and-white sinusoidal Gabor gratings presented one in each visual field quadrant and flickering one at a time at a 12 Hz rate. To assess response reliability a Signal-to-Noise Ratio analysis was conducted together with further analyses in time and frequency domains to make comparisons between groups (healthy participants and patients), side of brain lesion (left and right) and visual fields (sighted and blind).

The important overall result was that stimulus presentation to the blind hemifield yielded highly reliable responses with time and frequency features broadly similar to those found for cortical extrastriate areas in healthy controls. Moreover, in the intact hemifield of hemianopics and in healthy controls there was evidence of a role of prefrontal structures in perceptual awareness. Finally, the presence of different patterns of brain reorganization depended upon the side of lesion.

Keywords

1. Introduction

A lesion along the central visual pathway (from optic tract to visual cortex) often yields specific visual defects characterized by decreased vision or blindness of the contralesional visual field of both eyes, i.e. homonymous hemianopia (see Bouwmeester et al., 2007). In some cases, usually as a result of lesion of the optic radiation, the visual field defect may be limited to the upper or lower quadrant (quadrantanopia). More rarely, as a result of bilateral damage, a loss of vision of the superior or the inferior half of both visual hemifields may occur (altitudinal hemianopia). Thanks to the “revolutionary” discovery of Poppel et al. (1973) and Weiskrantz et al. (1974) of the existence of unconscious visually triggered responses, hemianopic patients have become a fundamental source of information on the neural mechanisms of visual perceptual awareness and on possible mechanisms of recovery from cortical blindness. Larry Weiskrantz defined as “blindsight” unconscious visually triggered behavior which was later subdivided into Type I and Type II according to the absolute lack of any form of perceptual awareness or to the presence of a “feeling” that a visual stimulus was presented, respectively (Weiskrantz, 1997). The study of the neural substrate of blindsight is obviously of crucial importance to understand the mechanisms enabling perceptual awareness. So far there have been several functional magnetic resonance imaging (fMRI) studies (see Ajina et al., 2015Bridge et al., 2010). Their contribution has provided important information but the temporal dynamics of the shift from unconscious behavior to blindsight of either Type I or II and possibly to full recovery of perceptual awareness require a much higher temporal resolution than fMRI, such as that ensured by electroencephalographic (EEG) methods.

Visual evoked potentials (VEPs) represent an EEG technique that measures variation of cortical activity as a function of time or frequency during repeated visual stimulation and can provide detailed information on the functional status of the visual system. Transient VEPs are the most used technique and are produced by slow-rate stimulus presentation (below 4 Hz) to allow the brain activity evoked by a stimulus to return to baseline level before the next stimulus is delivered. Transient VEPs have been frequently used not only in basic visual neurophysiology but also for the diagnosis of several optical and neurological pathologies. However, their use in the study of hemianopic patients has been very scanty albeit with some exceptions (Brecelj, 1991; Celesia and Brigell, 1999; Ffytche et al., 1996; Kavcic et al., 2015; Rossion et al., 2000; Schomer and Lopes da Silva, 2011). Shefrin et al. (1988) were the first to study the neural correlates of blindsight in hemianopic patients but found that visual stimuli (words) presented to the blind hemifield could not elicit a response except for one patient with clinical signs of blindsight out of four patients tested. This patient showed task-related late activity such as the P3 and some earlier components around 80–300 ms. They concluded that the kind of blindsight shown was not mediated by the geniculo-striate pathway. In keeping with this conclusion, early components peaking around 90–130 ms after stimulus onset have been found in later studies in healthy participants to arise from extrastriate visual areas (e.g. Di Russo et al., 2016). Furthermore, Kavcic et al. (2015) with moving visual stimuli did find VEP responses to stimulus-onset presentation from the damaged hemisphere but only when the intact hemifield was stimulated and therefore via interhemispheric connections. Interestingly, with motion-onset stimuli, VEP responses could be obtained only from patients with left hemisphere damage. Broadly similar results have been observed by Bollini et al. (2017) who studied the VEP responses to static and moving stimuli in two hemianopic patients with either right or left occipital lesion. Results clearly showed the presence of N1 and P2 components over the damaged hemisphere for both static and moving stimuli, and a late negative component (around 350 ms) in the intact hemisphere but only for moving stimuli and when stimulating the blind hemifield in the left lesioned patient who also showed blindsight. Authors suggested that interhemispheric transfer mechanisms subserved this kind of blindsight for moving stimuli.[…]

Continue —> Visually evoked responses from the blind field of hemianopic patients – ScienceDirect

Fig. 2

Fig. 2. Patients’ structural magnetic resonance images. Localization and extension of the lesions are drawn in red. A) right hemisphere lesion with resulting left hemianopia; B) left hemisphere lesion with resulting right hemianopia; and C) bilateral hemispheric lesion with resulting bilateral altitudinal hemianopia. Images are left-right oriented according to the radiological convention.

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[Case Study] Transcranial direct current stimulation (tDCS) combined with blindsight rehabilitation for the treatment of homonymous hemianopia: a report of two-cases – Full Text PDF

Abstract.

[Purpose] Homonymous hemianopia is one of the most common symptoms following neurologic damage leading to impairments of functional abilities and activities of daily living. There are two main types of restorative
rehabilitation in hemianopia: “border training” which involves exercising vision at the edge of the damaged visual field, and “blindsight training,” which is based on exercising the unconscious perceptual functions deep
inside the blind hemifield. Only border effects have been shown to be facilitated by transcranial direct current stimulation (tDCS). This pilot study represents the first attempt to associate the modulatory effects of tDCS over
the parieto-occipital cortex to blindsight treatment in the rehabilitation of the homonymous hemianopia.

[Subjects and Methods] Patients TA and MR both had chronic hemianopia. TA underwent blindsight treatment which was combined with tDCS followed by blindsight training alone. MR underwent the two training rounds in reverse order.

[Results] The patients showed better scores in clinical-instrumental, functional, and ecological assessments after tDCS combined with blindsight rehabilitation rather than rehabilitation alone. [Conclusion] In this two-case report parietal-occipital tDCS modulate the effects induced by blindsight treatment on hemianopia.

[Conclusion] In this two-case report parietal-occipital tDCS modulate the effects induced by blindsight treatment on hemianopia.

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