International meeting of the French society of neurology 2012Rehabilitation of damage to the visual brainRééducation après lésion du cerveau visuel
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.
References (75)
- et al.
Extrageniculostriate vision in the monkey. VI. Visually guided accurate reaching behavior
Brain Res
(1978) - et al.
Sustained extrastriate cortical activation without visual awareness revealed by fMRI studies of hemianopic patients
Vis Res
(2001) - et al.
Functional compensation of visual field deficits in hemianopic patients under the influence of different task demands
Vis Res
(2010) - et al.
Eye-fixation patterns in homonymous hemianopia and unilateral spatial neglect
Neuropsychologia
(1987) - et al.
Visually-guided behavior of homonymous hemianopes in a naturalistic task
Vis Res
(2007) - et al.
Visual field changes after a rehabilitation intervention: vision restoration therapy
J Neurol Sci
(2008) - et al.
Temporal properties of spatial channel of processing in hemianopia
Neuropsychologia
(2008) - et al.
The significance of visual information processing in reading: Insights from hemianopic dyslexia
Neuropsychologia
(2008) Homonymous hemianopia, a review of one hundred cases
Amer J Ophthol
(1962)Visual scanning behavior in patients with homonymous hemianopia
Neuropsychologia
(1995)