Posts Tagged Hemianopia

[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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[VIDEO] Hemianopia explained and simulated using an eye-tracker – YouTube

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[VIDEO] Visual Pathway and Lesions – YouTube

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[Abstract] From cortical blindness to conscious visual perception: Theories on neuronal networks and visual training strategies

Homonymous hemianopia (HH) is the most common cortical visual impairment leading to blindness in the contralateral hemifield. It is associated with many inconveniences and daily restrictions such as exploration and visual orientation difficulties. However, patients with HH can preserve the remarkable ability to unconsciously perceive visual stimuli presented in their blindfield, a phenomenon known as blindsight. Unfortunately, the nature of this captivating residual ability is still misunderstood and the rehabilitation strategies have been insufficiently exploited. This paper discusses type I and type II blindsight in a neuronal framework of altered global workspace, resulting from inefficient perception, attention and conscious networks. To enhance synchronisation and create global availability for residual abilities to reach visual consciousness, rehabilitation tools need to stimulate subcortical extrastriate pathways through V5/MT. Multisensory bottom-up compensation combined with top-down restitution training could target pre-existing and new neuronal mechanisms to recreate a framework for potential functionality.

Source: Frontiers | From cortical blindness to conscious visual perception: Theories on neuronal networks and visual training strategies | Frontiers in Systems Neuroscience

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[Abstract] Review of rehabilitation and habilitation strategies for children and young people with homonymous visual field loss caused by cerebral vision impairment

 

Abstract

Partial and homonymous visual field loss (HVFL) is a common consequence of post-chiasmatic injury to the primary visual pathway or injury to the primary visual cortex. Different approaches to rehabilitation have been reported for older adults with HVFL and there is evidence to support the use of compensatory training over other proposed therapies. We reviewed the literature to investigate the current state of the art of rehabilitation and habilitation strategies for children and young people with HVFL, and whether there is enough evidence to support the use of these strategies in the paediatric population. We have provided an overview of the existing literature on children and young people with HVFL, a brief overview of rehabilitation strategies for adults with HVFL, and evidence on whether these different interventions have been applied with children and young people effectively. We found that there have been very few studies to investigate these strategies with children and young people, and the quality of evidence is currently low. New research is required to evaluate which strategies are effective for children and young people with HVFL and whether new strategies need to be developed.

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Source: Review of rehabilitation and habilitation strategies for children and young people with homonymous visual field loss caused by cerebral vision impairment – The Lincoln Repository

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[VIDEO] Hemianopia explained and simulated using an eye-tracker – YouTube

Hemianopia explained and simulated using an eye-tracker

 

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[VIDEO] Computer Access for People with Hemianopia – YouTube

Strategies for adapting a computer for use by people with visual field deficits.

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