Elsevier

Revue Neurologique

Volume 168, Issue 10, October 2012, Pages 754-761
Revue Neurologique

International meeting of the French society of neurology 2012
Rehabilitation of damage to the visual brainRééducation après lésion du cerveau visuel

https://doi.org/10.1016/j.neurol.2012.07.015Get rights and content

Abstract

Homonymous visual field loss is a common consequence of stroke and traumatic brain injury. It is associated with an adverse functional prognosis and has implications on day-to-day activities such as driving, reading, and safe navigation. Early recovery is expected in around half of cases, and may be associated with a return in V1 activity. In stable disease, recovery is unlikely beyond 3 and certainly 6 months. Rehabilitative approaches generally target three main areas, encompassing a range of techniques with variable success: visual aids aim to expand or relocate the affected visual field; eye movement training builds upon compensatory strategies to improve explorative saccades; visual field restitution aims to improve visual processing within the damaged field itself. All these approaches seem to offer modest improvements with repeated practice, with none clearly superior to the rest. However, a number of areas are demonstrating particular promise currently, including simple web-based training initiatives, and work on neuroimaging and learning. The research interest in this area is encouraging, and it is to be hoped that future trials can better untangle and control for the number of complicated confounds, so that we will be in a much better position to evaluate and select the most appropriate therapy for patients.

Résumé

Une perte du champ visuel homonyme est fréquente après un trauma crânien. Elle est associée à un pronostic visuel défavorable avec des implications pour la vie de tous les jours comme la conduite, la lecture et la navigation en sécurité. Pour la moitié des cas, on peut espérer une récupération avec retour d’un niveau d’activité V1. Pour une maladie stabilisée, la récupération est peu probable après trois mois et à six mois la perte est irréversible. L’approche rééducative a trois objectifs, avec des techniques et des taux de succès variables : aides visuelles afin d’élargir ou relocaliser le champ visuel affecté ; entraînement des mouvements oculaires à partir des stratégies compensatoires afin d’améliorer les saccades exploratrices ; restitution du champ visuel pour améliorer le traitement visuel au sein même du champ endommagé. Lorsqu’elles sont répétées, ces différentes approches semblent permettre des améliorations modestes, sans avoir un effet clairement supérieur au repos. Cependant un certain nombre d’interventions, dont des initiatives d’entraînements sur le web et des travaux sur la neuroimagerie et l’apprentissage, montrent des effets prometteurs. La recherche dans ce domaine est encourageante. On peut espérer voir des essais futurs ayant un meilleur contrôle des facteurs confondants afin de mieux évaluer et sélectionner les patients susceptibles de profiter des thérapeutiques proposées.

Introduction

It is widely recognised that stroke is the most frequent cause of homonymous visual field defects (HVFD), with an estimation that between 40–86% of isolated HVFD are caused by posterior circulation ischaemia (Smith, 1962, Fujino et al., 1986, Trobe et al., 1973, Zhang et al., 2006a). Other common aetiologies include traumatic brain injury, tumour (each < 15%), and less frequently brain surgery and demyelination (Zhang et al., 2006a), with causative lesions most commonly in the occipital lobes (45%) and optic radiations (32.2%).

In the UK alone, there are approximately 150,000 new cases of stroke a year, with between 8-26% left with persistent hemianopia (Gilhotra et al., 2002, Gray et al., 1989), which may be closer to 30% acutely (Haerer, 1973). Figures vary quite extensively, however, with variable population demographics, measurement techniques, and reporting biases.

Stroke is also considered to be the most common cause of disability in adults (Hankey, 1999), and is likely to increase in the future with an aging population. Importantly, HVFDs in such patients are associated with an adverse functional prognosis, including likelihood of discharge home (Schlegel et al., 2003), mobility, and survival (Haerer, 1973, Gray et al., 1989). Functionally, HVFD may impair day-to-day activities including driving, reading and obstacle avoidance, which can cause reduced participation in social activities and quality of life (Trauzettel-Klosinski, 2011). At the other end of the spectrum, it is also worth noting that HVFDs often go unreported, perhaps overlooked or under-prioritised by clinicians, or because patients learn to compensate for their deficit (Zhang et al., 2006a, Gilhotra et al., 2002).

Section snippets

Early recovery

There has been some debate about how quickly recovery of HVFD takes place after brain injury, with reports varying from two weeks (Gray et al., 1989) to one year (Trauzettel-Klosinski, 2005). Zhang et al. (2006b) reviewed the medical records of 254 consecutive patients with HH over a 15-year period, and performed a regression analysis to determine probability of improvement (reduction in VFD more than 10° horizontally or 15° vertically) as a function of time after injury. Although this was not

Blindsight

As well as compensation to simply shift the field of view to the unaffected side, some work has suggested that saccadic eye movements (Barbur et al., 1988) and obstacle avoidance (Striemer et al., 2009) can be influenced by unseen stimulation within the blind hemifield.

“Blindsight” refers to the observation that certain stimuli within the blind hemifield can undergo processing and influence behaviour despite the individual often being completely unaware of their presence (Weiskrantz et al., 1974

Plasticity in the visual system?

Despite certain limitations, diffusion-weighted MRI offers a unique method to explore non-invasively the organization of white matter in the living human brain. Two important studies have employed this technique with probabilistic tractography following V1 damage. Leh et al. (2006) looked at four patients with previous hemispherectomy for intractable epilepsy. They subdivided patients into those with and without indirect blindsight, and suggested that those with blindsight showed unique

Rehabilitative approaches

Irrespective of the presence or absence of unconscious processing, hemianopic patients remain significantly impaired in day-to-day life. Here we detail the rehabilitative approaches designed to offer both practical improvements to the sighted field, as well as techniques designed to improve vision with training. There are currently three main approaches, incorporating a number of techniques of varying popularity and evidence. These include the use of visual aids, a number of eye movement

Functional imaging of rehabilitation

Henriksson et al. (2007) investigated the effects of training on changes in fMRI and MEG activation. Training involved a difficult detection task of flickering discs and recognition of flickering letters twice a week over 2 years. They found that after training, stimulation of the blind hemifield with a large reversing checkerboard activated contralesional V5, as well as V3a, and to a lesser extent V3, dorsal V2, and a border region between V1 and V2d. Although only MEG and not fMRI were

Conclusion

There are a number of rehabilitative techniques currently available, most of which offer specific and non-transferrable improvements in vision. No treatments to date claim to be able to fully restore vision to the damaged hemifield, although this remains the goal for restitution and plasticity-based research groups. The approach in other laboratories remains more pragmatic, focusing on the most effective ways to compensate for the deficit rather than looking for recovery. At this stage, it

Disclosure of interest

The authors declare that they have no conflicts of interest concerning this article.

Acknowledgements

SA is supported by the Wellcome Trust (WT096001/Z/11/Z) and CK by the NIHR Oxford Biomedical Research Centre.

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