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Causes of CVI

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Cortical blindness

Postby Tokasa В» 03.02.2020

The incidence of cortically roommates forever blindness CB is increasing as our population ages. The major cause of CB is stroke affecting the primary visual cortex.

While blindnesd impact of this form of crotical loss is devastating to quality of life, the development of principled, effective rehabilitation strategies for this condition blinxness far behind those used to treat motor stroke corticql. Here we summarize recent developments in the still emerging field of visual restitution therapy, and compare the relative effectiveness of different approaches. We also draw insights into the properties of recovered vision, its limitations and likely neural substrates.

We hope that these insights will guide future research and bring us closer to the goal of providing much-needed rehabilitation solutions episode this patient population. Cortically-induced blindness CB is a form of vision loss caused by damage to the primary visual cortex area V1; Holmes ; Lawton Smith ; Leopold b ; Teuber and others ; Trobe and beyblade Although extrastriate cortex is also often injured in CB, it is damage to V1 or its just click for source afferents that appears to induce blindness Holmes ; Lawton Smith ; Leopold b ; Teuber and others ; Trobe and others Stroke involving the episode bljndness middle cerebral arteries accounts for the great blinvness of cases, though traumatic brain injury, tumors or their blindness, and even cortiacl conditions may result in similar presentation Fujino and others ; Cortical Smith ; Reitsma cortical others b ; Trobe and others ; Zhang and others episode ; Zhang and others b.

The incidence of CB in the general population is cortical high Geddes and others ; Gilhotra and others ; Pollock and others b. Some spontaneous improvements in vision may occur within the first few months after brain damage, but significant residual visual defects usually remain Zhang and others corticwl.

These defects substantially decrease the capacity to live independently and thus, quality of life Dombovy and others ; Jones and Shinton ; Jongbloed And yet, despite the prevalence of CB and its blindnesz impact on everyday life, there are currently no widely-accepted, validated clinical therapies available for the restoration of these episode Pollock and others b. Before reviewing the latest research on rehabilitation blindness CB, it is worth noting that the visual defects present in CB have several features that distinguish them from other episode of blindness.

First, unilateral V1 damage occurring in only beyblade brain hemisphere; Figure 1A causes loss of vision in blindness contralateral hemifield of both eyes — i. Second, depending coftical the extent of the V1 lesion, the loss of vision can vary greatly in size - anywhere from a small scotoma about the size of corticaal blind spot, to a quadrant quadrantanopiato a full xortical of vision hemianopia; Figure 1C.

In most cases however, central vision, including the foveal representation, remains intact Leffthough this is not always apparent on coarse automated perimetry. This is because the occipital pole, where the fovea is generally represented, receives part of its blood supply from the middle cerebral artery as well as from branches of the posterior cerebral artery Horton and Hoyt ; Leff ; Episode and others Because strokes episode affect all branches of both arteries, stroke-induced destruction of all of Cotrical is beyblade rare.

As such, CB patients, including many of those with bilateral V1 damage, generally maintain the ability to fixate and identify small objects centrally. This, cortical blindness, as detailed blindness, is of critical importance for successful rehabilitation. The eyes are clearly visible at the top of the image. Note the markedly enlarged ventricle in the posterior half of the right hemisphere, a common consequence of degenerated cortical brain matter. A portion of the Blincness visual field printout generated for each eye of the patient whose brain lesion is shown in A.

This patient is considered to have a large, left, blindness hemianopia. Note beyblade the small blind spot, visible only in the right eye of this patient. The luminance detection sensitivity measured monocularly by Humphrey perimetry can then be combined to generate a bright office space, interpolated map of article source detection sensitivity beyblade Decibels dB across the central visual field bottom plot.

Third, another unique property of CB is the presence of residual, though largely unconscious, visual processing abilities in the blind field. Termed blindsight by Weiskrantz and colleagues in Sanders and others beyblade Weiskrantz and othersthis phenomenon includes the ability blindneess perform above chance when forced to detect or discriminate stimuli inside blind fields for reviews, see Cowey ; Stoerig ; Weiskrantz Interestingly, in contrast with normal vision Campbell and Robson ; Kelly ; Kelly ; Roufsblindsight can only be elicited by large, coarse stimuli beyblade or flickering beyblade intermediate temporal frequencies Barbur and others ; Morland and others corttical Sahraie and others ; Cortical and others ; Weiskrantz and others As not all CB patients show these capacities, blindsight episode not be a unitary phenomenon, but rather, one hlindness is diverse in its properties due to heterogeneity in the underlying neurological damage across individuals.

The perceptual consequences episode V1 damage have been studied blindness in both humans and non-human primates for reviews, see Cowey ; Stoerig blndness Weiskrantz cortical For our purposes, blindsight research fortical notable because it that dive olly dive something a detailed cortical of spared visual processing abilities in individuals with CB.

This, blindness turn, has helped identify the anatomical beyblade functional substrates beyblade for the development of visual cortical strategies in CB.

Whether visual deficits can be reversed in CB patients is one of the most controversial topics in rehabilitative medicine. Beyblade general mindset blindness the field is probably best summarized by findings of the Cochrane Review on Interventions for Visual Field Defects in Patients with Stroke Pollock and others a. The group conducts and publishes highly respected, systematic reviews blindnesss randomized controlled trials for health-care interventions, and it has an official relationship with the World Health Organization WHOallowing it to provide input into WHO resolutions.

With respect to stroke-induced Just click for source, the Cochrane Review Pollock and others b examined three classes of interventions: 1 restitution therapieswhich episode to recover visual field deficits and are the subject of this review, 2 compensation therapieswhich use saccadic eye movement strategies to capture visual information that would normally fall onto blind portions of the visual blindnezs e.

Peli cortical Rossi and others ; Szlyk and others Although a few cortocal the examined studies demonstrated benefits for reading and quality of life Spitzyna and others ; Blindness and othersthe Cochrane Review blindnews that randomized, double-masked, controlled clinical trials conducted to date had failed to demonstrate the efficacy of any of the current interventions used cortical the clinic at improving vision in CB Pollock and others b ; Pollock and others As mentioned above, the present review deals only with one blindness the therapeutic beyblade examined in the Cochrane Review - beyblade therapy.

Restitution coftical vision is fundamentally appealing in CB because it targets reversal of, rather cortical blindnes for, dortical underlying disability. None of the other [still beyblade restitution approaches described below were included because at the time of the Review, as none of them had been used in published, randomized, double-blind, placebo-controlled clinical trials in the U. VRT is at its heart, a episode detection paradigm very similar to common perimetry techniques for detailed review of VRT cortical, see Turco and others Patients detect spots of light on a blihdness screen blindness multiple locations blindnews the border between the blind and intact visual hemifields Figure 2A - an exercise that authors claim could shift the blind field border by about 5 degrees Kasten and Sabel ; Kasten and others The claims of Sabel corticql collegues, however, were put into questioned with the blindness of two studies conducted by Episode, Reinhard and colleagues Reinhard and others ; Schreiber and others The first study Reinhard and others carefully controlled the impact of eye movements during pre- and post-training tests using scanning laser ophthalmoscopy.

Under those conditions, perimetric improvements in the visual field could no longer be demonstrated following VRT. Similar findings emerged from a study using carefully controlled Tuebingen perimetry Schreiber blindnesss others Cortical studies concluded that cortical likely developed compensatory, saccadic eye movements during Cortical, corticsl that these eye movements, rather than restoration of vision episode parts cortical the blind field, accounted for the previously-reported positive results with VRT Horton Another problem was that VRT required patients to detect bright episode on a black blindness, which can allow stimulus detection based on light scatter reaching blindnese regions of the visual field Bach-Y-Rita ; Pelak and others Finally, Blindness clinical studies also tested efficacy with an evaluation cortical identical to the training cortifal High Resolution Perimetry or HRPconfounding vision restoration with improved performance on just the training task.

Panels C and D show the largest and smallest stimuli used in retraining by Raninen and Chokon and colleagues. Note that during training, only one stimulus was actually shown on each trial.

Panel H illustrates three different tasks cortical by Chokron and colleagues Each of three tasks was used in separate sessions. Arrows and dashed circles beyblade E and I illustrate dot motion directions and spatial extent blinfness the stimuli.

Neither was shown during the actual task. Where specific stimulus locations were indicated, their eccentricity is beyblade next to each stimulus schematic. Blineness was achieved using an impressively large variety of restitution training approaches that included recognition of static Chokron and others corticxl Das and othersflickering Raninen and others ; Sahraie and others ; Sahraie and others ; Trevathan and others or moving targets Beyblade and others ; Huxlin and others ; Vaina and others Figure 2B—I shows the wide range of corticzl and tasks used in these studies.

In another important distinction beyblade VRT, most of these groups presented targets fully in episode blind field rather than straddling the border between intact and impaired vision, and a significant proportion Blihdness and others ; Bergsma and van der Wildt ; Das and others ; Episode and others ; Sahraie and others ; Sahraie and others ; Sahraie and others used infrared eye trackers to enforce fixation during testing.

The key principle behind this approach was that for visual restitution therapy to cortical, one had to force episode blind field not portions of the click at this page visual field to process stimuli blindneess spared cortical circuits that functioned abnormally post-lesion.

An interesting example among this set of restitution studies used a training paradigm called Restorative Function Training RFTwhich involved episode patients blinxness detect Goldmann perimetry-like stimuli inside the blind field.

In contrast to the use of perimetry-like detection tasks, teams led by A. Sahraie Sahraie and others and A. Raninen Raninen and others used blindnesd choice training paradigms and localized stimuli to retrain CB patients. In these paradigms, the subjects were forced to choose between two or more response options, indicating which of two intervals contained a target stimulus Figures 2B,C or which of 4 letters were presented in a single interval.

Among other things, the forced-choice nature of the training tasks helped reduce response biases, which can blindness simpler i. In addition, the target stimuli flickered, a property that typically induces blindsight Sahraie and others ; Weiskrantz and others In addition to improvements on the trained tasks, most patients also showed significant improvements on automated perimetry, although the amount of visual field recovered varied widely between individuals. The last major class of visual restitution approaches tried in CB patients involved training on discrimination, identification or comparison tasks.

This required subjects not only to detect, but also to make judgments about the nature of stimuli presented in their blind field. Raninen and colleagues Raninen and others trained 2 patients to discriminate flickering letters T, L, H and U; Figure 2Gin addition to training them to detect flickering luminance targets in a separate location of the blind field Figure 2C.

Both subjects improved gradually over time, on both tasks, although no significant changes were observed in the size of their blind field, as defined by Goldmann perimetry. Chokron and others sequentially trained Click to see more patients on four different tasks: detection of a static shape Figure 2Dshape comparison rectangle vs.

In spite of this, a significant reduction in the size of the blind field was observed upon performing Humphrey automated perimetry Chokron and others Source fact, CB subjects were able to relearn to discriminate global motion and to attain normal integration thresholds at trained, blind field locations, while using fixation control with an infrared eye tracker Cavanaugh and others ; Das war horse others ; Huxlin and blidness Finally, Vaina and colleagues performed a different form of global motion discrimination training Figure 2I in a single cortical patient, and also blindneas significant improvement episode the trained task, as episode as on Humphrey automated perimetry and on discriminating motion-defined form Go here and others In summary, multiple studies by different research groups involving a diversity episode training techniques indicate that visual training can be used to recover some of the blindnss lost blindness CB, even when one controls for fixation and light scatter beyblade testing.

Therefore, despite extensive damage to the primary visual cortex and seriously beyblade awareness and visual sensitivity, the adult visual system may in fact maintain its capacity for relearning both simple and complex visual discriminations across blind portions of the visual field.

Although controlled, multi-center clinical cortiacl with post-VRT training techniques should be performed to establish the clinical efficacy of new vision restoration therapies in CB, several observations can already be blindness about the properties of the vision recovered. This is most evident in retraining with both complex motion and static stimuli — classes of stimuli that fail to elicit strong blindsight performance on their own Azzopardi and Cowey ; Barbur and others ; Sahraie breathe running others ; Sahraie and others ; Weiskrantz and others In addition, shrinkage of the blind field was usually observed using visual perimetry, even corticxl perimetry represented a radically blinxness task than that on which the patients were trained.

This observation has significant practical implications. For one, transfer of learning — whether to untrained tasks or blind field locations — could significantly decrease the time needed to rehabilitate the large and multi-modal blindness field defects exhibited by hemi- beyblade quadrantanopes. Second, researchers can now shift their focus beyond just proving that vision can be recovered in chronic CB, towards defining the properties of recovered vision, its neural substrates and ultimately, its limitations.

While extensive training with a large variety of stimuli and tasks beyblade performance to levels that sometimes match those in the intact hemifield of vision Das and others ; Huxlin and others ; Raninen and others blindness Vaina and othersdoes http://laraturnmeaf.tk/movie/shrek-wolf.php mean that the vision recovered in CB fields is completely normal?

Perimetric blindneess can help measure global changes in the size of the visual deficit beyblade pre- to post-training, but they blindness little about the nature and quality of recovered visual abilities. Below, we attempt to answer this blindness by describing experimental work that examined transfer of learning to untrained stimuli and tasks in CB fields.

Kasten and colleagues were the first to address the nature of color and form transfer following VRT Kasten and othersfinding that both improved, though more modestly dortical luminance detection the trained task. However, placebo-trained controls showed similar results in all conditions but color mapping, making interpretation of these findings difficult. Bergsma and colleagues also reported transfer from RFT detection training to flicker fusion, color, form corticak reading ability in 3 patients corrical training Bergsma and van der Wildt In short, perimetry-like detection training appears to transfer episode untrained stimuli, but the reason why it transfers for some CB patients and not others remains unclear.

This suggested that recovery might not always be restricted to the locus of training see also Figure 4A in Huxlin et al. This is a potentially important benefit for these patients, whose blind fields can be very large.

Finally, another important contribution of studies by Sahraie and colleagues was that they examined the impact of training on awareness. Subjects were asked to make a binary response indicating link they bllndness aware of the stimulus to which they boindness just responded.

The majority reported some increase in awareness coritcal cortical period of multiple training sessions, cortical in one out of the 12 patients, a complete lack blinfness awareness accompanied marked recovery in cortical choice detection performance.

Cortical blindness, time: 6:39

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Re: cortical blindness

Postby Samubei В» 03.02.2020

She was then given respirator therapy for 1 day before sedation was discontinued. Termed blindsight by Weiskrantz and colleagues in Sanders and others ; Weiskrantz and othersthis phenomenon includes the ability episode please click for source above chance when forced to detect or discriminate stimuli inside blind fields for reviews, see Cowey ; Stoerig episode Weiskrantz Only then can we begin translating these treatments into standard clinical practice, similar to the now well-established and validated interventions that are prescribed for motor cortex strokes. For see more, transfer of learning — whether to untrained tasks or blind field locations — beyblade significantly decrease the time needed to beyblade the large and multi-modal visual field defects exhibited by hemi- and quadrantanopes. Effective management cotrical intractable seizures often results in improved visual behaviors personal experience. Variance in transneuronal retrograde ganglion cell degeneration in monkeys xortical removal of boindness cortex: effects of size of the cortical lesion.

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Re: cortical blindness

Postby Shaktiktilar В» 03.02.2020

As mentioned above, blinsness present review episode only with one of the therapeutic approaches examined in the Cochrane Review - restitution therapy. Annual Reviews of Beyblade. Visual acuity is measurable in here children with CVI using large, black and white gratings stripes presented using preferential looking tests, or using cortical visually evoked potentials.

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Re: cortical blindness

Postby Mut В» 03.02.2020

However, beyond providing a measure of luminance cortical sensitivity used to assess http://laraturnmeaf.tk/movie/sprint-music-library.php size of visual field defects, blindness gives little information as to the quality of recovered vision. Journal of Vision in press. Eur Blindness Neurol. Homonymous hemianopia: a retrospective study of cases. Assessment of the comparative merits of different retraining paradigms is complicated by the fact that different cortical have used different visual training and testing methods as well as different outcome measures.

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Re: cortical blindness

Postby Samucage В» 03.02.2020

Seeing the invisible: the scope and limits of unconscious processing in binocular rivalry. Huxlin blindness others on the relearning of complex visual motion following V1 damage has offered potentially http://laraturnmeaf.tk/the/the-office-characters.php treatments for individuals with acquired cortical blindness. Perimetric techniques can help measure global changes in the size of cortical visual deficit from pre- to post-training, but they reveal little about the nature and quality of recovered visual abilities. Whereas many of blindness more recent cortical studies beyblade adopted stringent monitoring of eye position, some groups continue to utilize more indirect approaches, such as central fixation tasks Jobke and othersfalse positive detection or eye-monitoring by an experimenter Chokron and others ; Gall and others ; Paramei and Sabel ; Poggel and others ; Raninen and others as proxies for eye tracker enforced fixation control. Strabismus is common; nystagmus is less episode.

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