Posts Tagged Hemianopia

[BLOG POST] Management hemianopia

Hemianopia, partial loss of the field of vision, is a condition usually the result of a stroke although other neurological disorders such as tumours can be responsible.

From the Greek; hemi – half, an – without, opia – sight.

Damage to an individual’s brain in the area responsible for interpreting visual input is the most common cause;

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Normal field of vision

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Hemianopia

The thing about hemianopia is that often the person experiencing the condition is unaware. Imagine the entire right side of your world stops existing; your brain, just as with your physiological blind-spot very quickly recovers and compensates.

People who have experienced strokes will not uncommonly eat a meal and leave half the plate, not because they can’t see it (which they can’t), but because for that person there is no right or left side of the plate.

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We call this situation neglect. I guess that is apposite.

I first encountered this in Oliver Sack’s case histories. I can remember the story of a man waking-up in bed to find a strange object beside him; inert, disconnected – it was his own leg. (This might have been Alien Hand Syndrome, that is for another day.)

(For this reason, medical students, if you ever talk with someone who has experienced a major stroke, always make sure you are in their field of vision and not presenting as a disembodied voice.)

Once understanding this concept, I thought I would stretch the idea to include the way that certain branches of management operate.

It is all too easy for me to pick hospital management, but, what the heck.

Imagine you are running an organisation – it is perhaps doing OK, books balanced, care, treatment, production all at levels you anticipated at the start of the year; the plan is on plan. Beautiful; you can even go on holiday and chill-out.

If back home things go wrong; I don’t know, perhaps, the money that was thought to be in the bank is actually a deficit or, the equipment you have been using to undertake operations is in some way faulty, you have two options.

One, investigate, get as much information as possible, conclude and communicate.

The other, is to do the above, but pretend all is OK; assume that everything will be well – this, the ostrich strategy you might call it is more common within organisations than at first might seem logical; we have the 2007/8 Global Financial Crisis as a case study.

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Much analysis has happened since that time and is ongoing; in healthcare, our equivalent is the Mid Staffordshire Hospitals – is disaster the wrong word*? People running so fast on a treadmill that if they get off the uncertainty is more frightening than their high-speed collapse.

Good, clever, insightful people become blinded to what is obvious; hemianopia. It is there, it is clear to everyone else, but in the case of the afflicted it doesn’t exist.

Other words are lacuna, scotoma, absence.

Through careful therapy, a person can recover from hemianopia – utilising mirror-neurones, physical and psychological treatments, that which was lost can return.

How do we support those caught in management hemianopia to recover? Is there a treatment or a means of defence?

Be open, honest, vulnerable and candid.

Don’t hide behind false prophets or slogans.

Acknowledge that the world is never entirely knowable; accept dissonance. Ask for help.

And, if the humility isn’t there? If the situation is extreme and the walls falling-down?

What would you do?

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*Officially it was a ‘scandal’

via Management hemianopia – almondemotion

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[Abstract] A Systematic Review and Meta-Analysis of Rehabilitative Interventions for Unilateral Spatial Neglect and Hemianopia from 2006 through 2016

Abstract

Objective

To evaluate the effectiveness of activity-based, non-activity-based, and combined activity- and non-activity-based, rehabilitative interventions for individuals presenting with unilateral spatial neglect (USN) and hemianopia.

Data Sources

We searched CINAHL, Cochrane Library, EMBASE, MEDLINE and PubMed from 2006 to 2016.

Study Selection

Randomized controlled trials (RCTs), with a score of 6 or above in the PEDro Scale, that examined the effects of activity-based and non-activity-based rehabilitation interventions for people with USN or hemianopia. Two reviewers selected studies independently.

Data Extraction

Extracted data from the published RCTs. Mean differences (MD) or Standardized mean differences (SMD), and 95% confidence intervals (CIs), were calculated. Heterogeneity was assessed using the I2 statistic.

aData Synthesis

Twenty RCTs for USN and five for hemianopia, involving 594 and 206 stroke participants respectively, were identified. Encouraging results were found in relation to activity-based interventions for visual scanning training and compensatory training for hemianopia (MD=5.11; CI=0.83 to 9.4; P=0.019; I2=25.16% on visual outcomes), and optokinetic stimulation and smooth pursuit training for USN (SMD=0.49, CI=0.01 to 0.97, P=0.045, I2=49.35% on functional performance in activities of daily living; SMD=0.96; CI=0.09 to 1.82; P=0.031; I2=89.57% on neglect).

Conclusions

Activity-based interventions are effective and commonly used in the treatment of USN and hemianopia. Non-activity-based and combined approaches, for both impairments, have not been refuted, as more studies are required for substantiated conclusions to be drawn.

via A Systematic Review and Meta-Analysis of Rehabilitative Interventions for Unilateral Spatial Neglect and Hemianopia from 2006 through 2016 – Archives of Physical Medicine and Rehabilitation

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[WEB SITE] Hemianopia: Types, causes, symptoms, diagnosis, and treatment

hemianopiaHemianopia, also referred to as hemianopsia, comes from a culmination of three different Greek words: “hemi” translates to “half,” “an” translates to “without,” and “opsia” translates to “vision.” Hence, it literally means “being without half of your vision.”

This is a condition where half of your visual field can either be completely blind or partially diminished as a result of head trauma, a tumor, or suffering a stroke.

People who suffer from migraine headaches may sometimes experience temporary hemianopia or other visual disturbances, but this typically subsides on its own after a migraine goes away.

Homonymous hemianopia occurs when you lose part of your visual field on the same side of both eyes. This happens frequently to stroke patients or people who’ve suffered traumatic brain injuries. Visual images that are captured on the left side of the brain are communicated to the right side and vice versa, which is why hemianopia typically affects the same side of each eye equally.

The opposing posterior sides of the brain correspond to the opposite eye, which means that if an injury occurs on the left side of the brain, the visual field defects occur in the right eye.

What are the types of hemianopia?

As an umbrella medical term, there are actually five types of hemianopia and two subcategories in total. In fact, the hemianopia type that a patient suffers from is typically correlated with the exact site of the visual field defect.

Homonymous hemianopia

Visual field is lost on the same side in both eyes, depending on which side of the brain is affected by a stroke or injury. The left optic nerve controls the right visual field and the right optic nerve controls the left visual field. The diminished vision is instrumental in helping doctors locate the exact area of the brain that’s been injured or where the stroke occurred.

Heteronymous hemianopia

Loss of vision occurs in different fields of the eyes. Heteronymous hemianopia is separated into two different categories:

Binasal hemianopia: Blindness or vision loss occurs in the field of vision that’s within the closest proximity to the nose. This is caused by lateral damage to the retinal nerve fibers that don’t cross in the optic chiasm. They’re also responsible for registering information and sending it to the temporal retina.

Bitemporal hemianopia: As the name suggests, bitemporal hemianopia is a loss of vision that happens on the side of the eyes that’s closest to the temple. Lesions and damage to the optic chiasm can cause bitemporal hemianopia. The optic chiasm is located near the pituitary gland where the nerves from the left and right eyeballs meet and cross over one another to reach the opposite side of the brain.

Quadrantanopia

Loss of vision occurs in one quadrant or portion of the visual field, and this usually depends on the part of the brain that’s damaged. The area that’s connected to the damaged portion of the brain will suffer either partial or complete hemianopia.

Superior hemianopia:Superior hemianopia is when loss of vision occurs in the upper visual field of either the left or right eye or both.

Inferior hemianopia:Inferior hemianopia is when loss of vision occurs in the lower visual field of either the left, right, or both eyes.

What causes hemianopia?

There are several different factors or injuries that can cause hemianopia including brain injuries, strokes that occur in certain parts of the brain, and physical head trauma.

As mentioned, while severe migraines can cause temporary hemianopia and adversely affect the patient’s vision, this symptom typically subsides on its own once the migraine pain is relieved.

However, there are more permanent and hazardous causes of permanent hemianopia.

Brain injuries

Damage to certain parts of the brain such as blunt force trauma due to an accident or sports injuries accumulated over an extended period of time can lead to hemianopia in the visual fields of the eyes. These injuries can incur the growth of lesions or contusions on the brain over long periods of time, which can cause hemianopia in old age or even earlier on in life depending on the severity and frequency of the injuries.

Brain tumors

As brain tumors begin to form and continue to grow over time, they can have the same effects as traumatic brain injuries. Eventually, the pressure and damage caused by the tumor can directly result in hemianopia in either one or both of the eyes.

Stroke

Strokes typically occur as a result of insufficient supply of oxygen reaching the brain. Oxygen is important because it promotes healthy and stable cranial functions. The blockages happen for a number of reasons, the most common one being the formation of blood clots. Depending on the severity of the stroke, it could be fatal for the person who endures it. While survival is certainly preferable, it also means enduring various physical and mental ailments, including hemianopia.

What are the symptoms of hemianopia?

Hemianopia has a variety of signs and symptoms that are associated with it, including the following:

  • Loss of peripheral vision on one or both sides of the face
  • Loss of visual awareness
  • Constantly bumping into people or objects on a regular basis
  • Failing to notice objects or people on the side of the face where the hemianopia damage has occurred
  • Inability to process entire sentences, phrases, or words when reading due to disturbed or interrupted visual patterns
  • Visual hallucinations, as in seeing things that aren’t necessarily there such as certain lighting effects

In addition to the physical indicators of hemianopia, there are also a few psychological, emotional, cognitive, and even social repercussions. Many patients who suffer from hemianopia can become increasingly frustrated or frightened as their condition worsens because it can make mobility and attending social events extremely difficult. As a result, this loss of field vision can also have a negative effect on a person’s ability to live independently and a lot of patients may become gradually reclusive because they fear the outside world and enduring potential injuries.

Mounting irritation, aggravation, and stress also accompany hemianopia because people who suffer from it constantly think that people are bumping into them or objects are appearing out of nowhere. This can make it virtually impossible to function normally in crowded places. Part of the problem is that a lot of people don’t even realize that they have hemianopia until they’re officially diagnosed with it.

How is hemianopia diagnosed?

In order to accurately diagnose hemianopia, your optometrist will most likely send you to a specialist who will then conduct a series of tests on your vision. They’ll start off by asking you a series of questions with the intent of gaining a thorough and clear understanding of the symptoms you’re experiencing. You’ll also undergo a series of visual tests using a machine called a Humphrey Field Analyzer.

This machine tests the depth of vision in each eye individually. It flashes lights in each possible point of your vision including the upper left, lower left, upper right, lower right, and the center. All you have to do is press a button to indicate when you see the light. If the machine detects that you’ve missed the light multiple times in the same areas, it’ll determine that there may be blank patches within your visual field and this is an indication that you may have hemianopia.

Following this assessment, if it’s determined that you do have hemianopia, your doctor may then order a series of MRI tests to establish the initial cause of this condition, whether it was a brain injury, stroke, or a tumor.

How is hemianopia treated?

It’s important to note that while hemianopia treatments can be highly effective and rehabilitative, there’s no actual cure for this condition and you will have to continuously undergo various relief methods that can only stand to improve the condition and make it more manageable.

That said, the following is a list of treatment options for hemianopia. It’s up to your doctor to determine which one would be the most suitable for you depending on the type and severity of the hemianopia you have. In some cases, it might even be appropriate and useful to incorporate a combination of these treatments. Again, your doctor will typically use their own expertise and discretion in such cases.

Visual restoration therapy

This is provided by NovaVision and uses computerized software to help improve patients’ vision in half-hour increments where the patient is instructed to focus their gazes on a specified point and must move their head whenever they see a flash of light or other stimuli in their field of vision. This information is recorded by the computer and the treatment is adjusted with each session and progress of the patient.

Audio-Visual stimulation training

This is a multi-sensory visual training approach to attempting to improve the visual fields of people who suffer from hemianopia and it’s especially effective for treating homonymous hemianopia. It stimulates both the auditory and visual senses in an attempt to get them to work harmoniously with one another and improve the patient’s quality of life despite having this condition.

Optical visual span expanders

These are specialized sunglasses that are formulated specifically for each individual patient and their level of hemianopia. The sunglasses have prisms embedded in their lenses that can help enhance the patient’s vision and expand their field of vision while wearing them.

Explorative saccade training

Also referred to as scanning therapy, this technique tests the speed and correlation with which both eyes move from one focal point to another. The optometrist will observe as the patient’s eyes jet from one vertical or horizontal focal point to another and examine whether the eyes separate or move in unison. People who suffer from hemianopia are taught to incorporate this visual technique in their everyday lives to help them naturally expand their field of vision in every direction.

How does hemianopia effect everyday life?

Hemianopia can have a detrimental effect on a person’s everyday life if left untreated. Especially as people get older, they tend to become more reclusive due to this condition because they feel like burdens to their loved ones and everyone around them. People with diminished eyesight may have a hard time moving around without bumping into people or objects and because their line of vision is diminished as well, they most likely will have to surrender their driving privileges as well. This can make them feel like an even greater burden on their family and friends if they need to be driven everywhere or require the special assistance of a loved one or caregiver.

Hemianopia will undoubtedly have a strong impact on your everyday life, but that doesn’t mean it has to hold you back from being able to resume your regular activities or from doing the things you enjoy. By learning proper management and adaptation techniques, you can learn to live with and even conquer symptoms associated with hemianopia. If you’ve recently suffered a stroke, brain injury, or tumor and are noticing a vast decline in your vision, express these concerns to your doctor immediately so that they can start taking steps to administer a helpful treatment plan.

Related: How to improve vision: 11 home remedies to improve eye health

Related Reading:

Blurred vision in one eye: Causes, symptoms, and home remedies

Ocular migraine (retinal migraine): Causes, symptoms, and treatment

Sources:

https://books.google.co.in/books?id=tdODr5fpxEAC&pg=PA992&lpg=PA992&dq=Heteronymous+Hemianopia&source=bl&ots=7eMadgAuZ5&sig=VfCOZ_8hCtqijgXOOGKrlICn8ao&hl=en&sa=X&ved=0ahUKEwjv5Nakvv_YAhVJrY8KHeXgAZEQ6AEIrAEwFw#v=onepage&q=Heteronymous%20Hemianopia&f=false
http://www.eyesearch.ucl.ac.uk/es/es_hemianopia.php
https://www.revolvy.com/main/index.php?s=Binasal%20hemianopsia

 

via Hemianopia: Types, causes, symptoms, diagnosis, and treatment

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[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

Related Links

http://www.ialvs.com

 

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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[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] 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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