Efficacy of Neuro-Optometric visual rehabilitation in Homonymous Hemianopia

OBJECTIVES

To assess oculomotor dysfunction and the effectiveness of neuro-optometric visual rehabilitation in improving oculomotor parameters in participants with homonymous hemianopia.

MATERIALS AND METHODS

Fifty subjects diagnosed with homonymous hemianopia (HH), referred through the neuro-ophthalmology department, were recruited for the study. All the subjects underwent a detailed neuro-optometric evaluation that included testing for sensory, visuo-motor and oculomotor functions. Subjects with homonymous hemianopia were then prescribed with yoked prisms and were randomized to two treatments at one month, namely group 1: yoked prisms (n = 15) and group 2: yoked prisms with in-office visual search training (n = 15).

RESULTS

The mean ± SD age of the subjects was 46 ± 12 years. Subjects with HH exhibited a significant delay in the completion time, response and accuracy of tasks on proactive, saccadic and visual search parameters using the SVI compared to age-matched controls (Independent t-test, p < 0.05). A significant improvement in the reading speed and visual search parameters (RM ANOVA, p < 0.001) was seen post neuro-optometric visual rehabilitation with both yoked prisms and SVI. Statistically significant differences were observed in the reaction time of the visual search paradigms between the two rehabilitative modalities yoked (group1), yoked and SVI (group2) (Mann-Whitney U test, p < 0.001), with the group 2 showing better visual search performance outcomes compared to group 1 (yoked).

CONCLUSION

Visual search parameters among participants with homonymous hemianopia improved following combined rehabilitation (yoked prisms and visual search trainng).

Visual rehabilitation training alters attentional networks in hemianopia: An fMRI study

OBJECTIVE

Hemianopia is a visual field defect following post-chiasmatic damage. We now applied functional magnetic resonance imaging (fMRI) in hemianopic patients before and after visual rehabilitation training (VRT) to examine the impact of VRT on attentional function networks.

METHODS

Seven chronic hemianopic patients with post- chiasmatic lesions carried out a VRT for five weeks under fixation control. Before vs. after intervention, we assessed the area of residual vision (ARV), contrast sensitivity function (CSF) and functional MRI data and correlated them with each other.

RESULTS

VRT significantly improved the visual function of grating detection at the training location. Using fMRI, we found that the training led to a strengthening of connectivity between the right temporoparietal junction (rTPJ) to the insula and the anterior cingulate cortex (ACC), all of which belong to the cortical attentional network. However, no significant correlation between alterations of brain activity and improvements of either CSF or ARV was found.

CONCLUSION

Visual rehabilitation training partially restored the deficient visual field sectors and could improve attentional network function in hemianopia.

SIGNIFICANCE

Our MRI results highlight the role of attention and the rTPJ activation as one, but not the only, component of VRT in hemianopia.

Homonymous Hemianopia and Vision Restoration Therapy

Homonymous hemianopia from stroke causes visual disability. Although some patients experience spontaneous improvement, others have limited to no change and may be left with a severe disability. Current rehabilitation strategies are compensatory and cannot restore function. Animal studies suggest that central nervous system plasticity could allow for redirection of lost visual function into undamaged areas of cortex. A commercial therapy system was developed, from which claims of visual field expansion were disputed by independent researchers. The treatment remains controversial with seemingly contradictory data being generated. Continued research is underway to demonstrate the (non-)efficacy of this treatment method.

The Effects of Compensatory Scanning Training on Mobility in Patients with Homonymous Visual Field Defects: Further Support, Predictive Variables and Follow-Up

Introduction

People with homonymous visual field defects (HVFD) often report difficulty detecting obstacles in the periphery on their blind side in time when moving around. Recently, a randomized controlled trial showed that the InSight-Hemianopia Compensatory Scanning Training (IH-CST) specifically improved detection of peripheral stimuli and avoiding obstacles when moving around, especially in dual task situations.

Method

The within-group training effects of the previously reported IH-CST are examined in an extended patient group. Performance of patients with HVFD on a pre-assessment, post-assessment and follow-up assessment and performance of a healthy control group are compared. Furthermore, it is examined whether training effects can be predicted by demographic characteristics, variables related to the visual disorder, and neuropsychological test results.

Results

Performance on both subjective and objective measures of mobility-related scanning was improved after training, while no evidence was found for improvement in visual functions (including visual fields), reading, visual search and dot counting. Self-reported improvement did not correlate with improvement in objective mobility performance. According to the participants, the positive effects were still present six to ten months after training. No demographic characteristics, variables related to the visual disorder, and neuropsychological test results were found to predict the size of training effect, although some inconclusive evidence was found for more improvement in patients with left-sided HVFD than in patients with right-sided HFVD.

Conclusion

Further support was found for a positive effect of IH-CST on detection of visual stimuli during mobility-related activities specifically. Based on the reports given by patients, these effects appear to be long-term effects. However, no conclusions can be drawn on the objective long-term training effects.

Validation of a Reading Assessment for Persons With Homonymous Hemianopia or Quadrantanopia

OBJECTIVE

To preliminarily validate the Visual Skills for Reading Test (VSRT) for assessing reading performance in persons with homonymous hemianopia (HH) or quadrantanopia.

DESIGN

Retrospective chart review.

SETTING

University-based outpatient low vision rehabilitation center.

PARTICIPANTS

Persons (N=38) with HH or quadrantanopia who completed the VSRT.

INTERVENTIONS

Validation procedures included testing for equivalence of the 3 test versions, estimation of internal consistency reliability, and known-group comparison using VSRT results from previous studies of adults with normal vision and central field loss.

MAIN OUTCOME MEASURES

Corrected reading rate, reading accuracy rate, type and number of reading errors, and completion time were recorded and evaluated.

RESULTS

Cronbach α for the VSRT across all participants was .80, which indicated good internal consistency. A known-group comparison showed that persons with a visual field deficit read significantly slower than did normally sighted adults (t580=10.13; P<.0001). Persons with quadrantanopia read significantly faster than did persons with HH (t36=2.25; P=.03) or those with central field loss (t48=3.17; P=.0027). These findings confirmed that the VSRT correctly discriminated between groups in terms of reading performance.

CONCLUSIONS

Preliminary validation results indicate that the VSRT demonstrates adequate evidence of reliability and validity to evaluate reading performance in adults with HH or quadrantanopia.

[New approaches to visual rehabilitation training for patients with visual field defects]

In clinical practice, maculopathy and neurological eye disorders often cause visual field defects. Once the defects are formed, treatment and rehabilitation are confronted with the bottleneck due to irreversibility. With the transformation of medical patterns and people's higher needs for rehabilitation, new approaches to visual training for these diseases with visual field defects are emerging. Currently, visual rehabilitation training for patients with visual field defects focuses on two directions: central visual field defects and hemianopia / peripheral visual field defects. Patients' fine vision is mainly affected by central visual field defects, the rehabilitation training for which can be divided into eccentric viewing training, eye movement training and perceptual learning training. Patients' visual exploration, orientation, walking and reading are largely influenced by hemianopia and peripheral visual field defects, the rehabilitation training for which can be separated into visual restoration strategy and eye movement compensatory strategy.

Multisensory training reverses midbrain lesion-induced changes and ameliorates haemianopia

Failure to attend to visual cues is a common consequence of visual cortex injury. Here, we report on a behavioural strategy whereby cross-modal (auditory-visual) training reinstates visuomotor competencies in animals rendered haemianopic by complete unilateral visual cortex ablation. The re-emergence of visual behaviours is correlated with the reinstatement of visual responsiveness in deep layer neurons of the ipsilesional superior colliculus (SC). This functional recovery is produced by training-induced alterations in descending influences from association cortex that allowed these midbrain neurons to once again transform visual cues into appropriate orientation behaviours. The findings underscore the inherent plasticity and functional breadth of phylogenetically older visuomotor circuits that can express visual capabilities thought to have been subsumed by more recently evolved brain regions. These observations suggest the need for reevaluating current concepts of functional segregation in the visual system and have important implications for strategies aimed at ameliorating trauma-induced visual deficits in humans.

Bitemporal hemianopia; its unique binocular complexities and a novel remedy

Bitemporal hemianopic visual field impairment frequently leads to binocular vision difficulties. Patients with bitemporal hemianopia with pre-existing exophoria complain of horizontal diplopia, sometimes combined with vertical deviation (with pre-existing hyperphoria). The symptoms are a result of the phoria decompensating into a tropia (hemi-slide) due to the lack of retinal correspondence between the remaining nasal fields of both eyes. We measured these effects using a dichoptic perimeter. We showed that aligning the eyes with prisms could prevent diplopia if the bitemporal hemianopia is incomplete. We also describe the successful use of a novel fusion aid - the 'stereo-typoscope' - that utilizes midline stereopsis to prevent diplopia resulting from hemi-sliding in patients with complete bitemporal hemianopia.

Homonymous hemianopia and related visual defects: Restoration of vision after a stroke

The term homonymous hemianopia refers to visual impairment due to a post-chiasmatic brain lesion. Mammalian neurons of the central nervous system do not have the ability to regenerate. However, the cerebral cortex shows plasticity in certain cases. Motor or speech disorders due to frontal lobe brain damage can be improved with well-directed rehabilitation techniques. If such plasticity is possible, it raises the question whether specialized training could improve a cortical visual disorder. There is need for simple visual training which could be used in rehabilitation. A few different approaches have been developed to treat patients with hemianopia: (1) substitution including special devices, such as optical prisms; (2) compensation using intact residual abilities - especially training of eye movements; (3) restitution which is based on stimulating the blind hemifield. The third method of rehabilitation is the most controversial; however, it has the largest potential. To support concepts of the targeted rehabilitation outlined here, first: further development of the theory of plasticity in visual pathways is required and second: the efficacy of the rehabilitation procedures has to be demonstrated by clinical evidence. We review methods and approaches of hemianopia rehabilitation and treatment. We also review results of contemporary clinical studies and meta-studies.

[Emphasize the importance of study on treatment and visual restoration related to impairment of retro-chiasmal visual pathway]

Homonymous visual field defect which is usually caused by stroke, brain tumor and trauma, is common. In spite of partial spontaneous recovery, homonymous hemianopia still causes serious disability. Visual restoration therapy (VRT) based on the residual visual capability and brain plasticity theory was reported effectively enlarged visual field caused by impairment of visual pathway. Controversy still exits on the efficacy of these procedures. However, due to the high prevalence and poor outcome of visual pathway impairment, it is important to initiate multiple disciplinary co-operative study on VRT and other procedures for visual function rehabilitation to improve life quality of patients with retro-chiasmal visual pathway impairment.

Compensatory strategies following visual search training in patients with homonymous hemianopia: an eye movement study

A total of 29 patients with homonymous visual field defects without neglect practised visual search in 20 daily sessions, over a period of 4 weeks. Patients searched for a single randomly positioned target amongst distractors displayed for 3 s. After training patients demonstrated significantly shorter reaction times for search stimuli (Pambakian et al. in J Neurol Neurosurg Psychiatry 75:1443-1448, 2004). In this study, patients achieved improved search efficiency after training by altering their oculomotor behaviour in the following ways: (1) patients directed a higher proportion of fixations into the hemispace containing the target, (2) patients were quicker to saccade into the hemifield containing the target if the initial saccade had been made into the opposite hemifield, (3) patients made fewer transitions from one hemifield to another before locating the target, (4) patients made a larger initial saccade, although the direction of the initial saccade did not change as a result of training, (5) patients acquired a larger visual lobe in their blind hemifield after training. Patients also required fewer saccades to locate the target after training reflecting improved search efficiency. All these changes were confined to the training period and maintained at follow-up. Taken together these results suggest that visual training facilitates the development of specific compensatory eye movement strategies in patients with homonymous visual field defects.

Visual field defects after stroke--a practical guide for GPs

BACKGROUND

Visual field defect after stroke can result in significant disability and reduction in quality of life. Visual rehabilitation aims to maximise the residual vision and decrease functional disability. Understanding the rehabilitation options available, and where to refer patients with visual defects after a stroke, can help patients, and their families, in the rehabilitation process.

OBJECTIVE

This article provides a review of the functional disability from visual field loss and discusses the various forms of visual rehabilitation.

DISCUSSION

Optical therapy, eye movement therapy and visual field restitution are the rehabilitation therapies currently available. Rehabilitation needs to cater to each patient's specific needs. Any patient recognised as having a visual field defect after stroke needs prompt referral for further assessment and consideration for visual rehabilitation.

[Transcranial magnetic stimulation in the therapy of selected post-stroke cognitive deficits: aphasia and visuospatial hemineglect]

Over the last several years functional neuroimaging studies and neurophysiological investigations have provided greater insight into the mechanisms underlying neuroplasticity and recovery after stroke. Various techniques became available for the non-invasive modulation of human brain activity and allowed better rehabilitation programmes to be designed. One of these new techniques is transcranial magnetic stimulation (TMS). It is a painless brain stimulation technique that modulates cortical activity. Regularly repeated TMS delivered to a single scalp position (repetitive TMS, rTMS) has an effect on cortical excitability that lasts beyond the duration of the rTMS applications. The effects of rTMS on cortical excitability may be inhibitory or facilitatory depending on stimulation parameters. A growing number of studies consider rTMS as a potential therapeutic technique in neurological disorders. This method can be used as a complementary treatment to conventional therapy based on training of disturbed functions. In this review, we cite studies indicating that sessions of rTMS could improve some of the cognitive symptoms after stroke.

From blindsight to sight: cognitive rehabilitation of visual field defects

PURPOSE

Traditionally, post-chiasmatic lesions were believed to result in complete and permanent visual loss in the topographically related areas of the visual field. However, a number of studies with monkeys, and later with humans, have demonstrated spared implicit visual functioning, referred to as 'blindsight'. The present study assessed whether training this phenomenon would induce an objective restoration of conscious vision in the blind field of hemianopic patients.

METHODS

For a period of 22 weeks nine patients with unilateral occipital damage participated in several forced-choice visual tasks known to elicit blindsight: pointing to visual targets, letter recognition, visual comparison between the two hemifields, target localization, and letter identification. Before and after rehabilitation, patients were submitted to a behavioral pre- and post-test, including visual detection and letter identification as well as to automated perimetry visual field testing (Humphrey Automated 24-2 Full Threshold).

RESULTS

An objective improvement was found in the behavioral tasks for all patients at the post-test stage as well as an objective enlargement of the contralesional visual field for all except one of the nine patients. An overall decrease is seen in the number of undetected points (out of 30) on automated perimetry visual field testing after rehabilitation (F (1, 16)=22.57; p<0.001) for both eyes (Right Eye, RE: T=0; z=2.52; p<0.05; Left Eye, LE: T=0, z=2.37; p<0.05) regardless of lesion side.

CONCLUSIONS

The results suggest that explicit (conscious) visual detection can be restored in the blind visual field by using implicit (unconscious) visual capacities. Results are discussed regarding visual field defect rehabilitation, blindsight, attention, and brain plasticity hypotheses.

Long-term effects of prism adaptation on chronic neglect after stroke

Previous studies have discussed the effectiveness or ineffectiveness of prism adaptation for neglect patients.

PURPOSE

The aim of present study was to determine the long-term effect of prism adaptation with activity performance instead of pointing performance on chronic neglect patients.

SUBJECTS

Seven patients with chronic unilateral spatial neglect were recruited.

METHODS

We performed an 8-week intervention using prismatic glasses. Changes in eye movement before and after intervention were measured using an eye mark recorder system. We also assessed intentional spatial bias in terms of center of gravity in the standing position using a tactile sensor scan system. Additionally, regional cerebral blood flow was measured using SPECT (IMP) before and after intervention.

RESULTS

Eye movements significantly improved on the neglected side (p<0.01), and the effects were sustained for up to 6 weeks after the removal of the prism. The center of gravity significantly moved to the left and forward. Furthermore, rCBF showed a significant increase at the parietal cortex, pericalleosal area of the left hemisphere (P<0.05).

CONCLUSION

These results suggest that intervention using prismatic glasses could improve eye movement on the neglected side and correct intentional spatial bias. Prism intervention might be one valuable method for the activation of the important areas of the brain in neglect patients.

Properties of the regained visual field after visual detection training of hemianopsia patients

PURPOSE

To study the quality of the visual field areas that were regained after training. In those areas, we measured some of the elementary visual properties that make up the quality of visual functioning in daily-life. This was to provide information about whether the functional visual field had been enlarged.

METHODS

Patients with visual field defects after a CVA were trained to detect stimuli presented in the border area of the visual field defect. Then, in the regained areas, we measured visual acuity as a measure for spatial properties. Secondly, to assess for temporal properties we measured critical flicker frequency (CFF). Finally, we studied color vision as a third property of the regained areas.

RESULTS

Since we could not predict where restoration of visual fields would occur, we did not present pre-post comparisons. However, despite the fact that training was carried out with simple white light stimuli, we could assess acuity, CFF and color vision in the regained areas. The performance of the patients during testing of the elementary properties appeared to be almost normal when compared to control subjects and comparable to the patient's own ipsilesional visual field.

CONCLUSIONS

These results support the idea that the regained visual fields that emerged after training are actually used for processing additional visual stimuli other than those used during training.

Multifactorial predictors and outcome variables of vision restoration training in patients with post-geniculate visual field loss

PURPOSE

Systematic stimulation of the visual field border in patients with visual field loss after cerebral lesions improves visual function even years after the onset of partial blindness. However, computer-based training programs like Vision Restoration Training (VRT) are not equally effective in all patients. We therefore tested which factors determine training outcome and which visual and cognitive functions are changed by VRT.

METHODS

Multiple outcome measures were predicted using a multifactorial regression approach. Nineteen patients with post-geniculate visual system lesions performed six months of VRT and underwent extensive testing before and after treatment, including visual field measurements, attention functions, and subjective parameters.

RESULTS

Visual field size increased significantly during training, but a number of cognitive, especially attentional, variables also improved, as did subjective visual function. The size of areas of residual vision was the strongest predictor variable for visual field increase. Demographic and lesion-related variables had little influence on training success.

CONCLUSIONS

With multivariate regression models, training outcome on different variables can be accurately predicted. Moreover, visual field increase is sufficiently predictable based on a set of variables readily available to the clinician: age of the patient, time since lesion, number of absolute perimetric defects, eccentricity of the visual field border, size of areas of residual vision, and average reaction time to perimetric stimuli.

The visual performance test: indications for compensational visual rehabilitation training and first results

The visual performance test (Dannheim & Verlohr, 2007) measures the time required to find an object within the visual field. Black icons of high contrast are superimposed on a scenic background of low contrast in one of 11 positions in random order. The subject's task is to find the search icon on the CRT screen as rapidly as possible. This test was administered binocularly in 38 patients with homonymous visual field defects. The aim of the test was to identify those patients who had not adapted themselves to their visual handicap, and to quantify the effect, in these patients, of training of compensational search saccades (Meienberg et al., 1981; Nelles et al., 2001; Trauzettel-Klosinski, 2004). The results show that the visual performance test reflects the practical abilities of these patients and that it may monitor the benefit of visual rehabilitation training in patients with functional restrictions in daily life.

Recovery of visual fields in brain-lesioned patients by reaction perimetry treatment

BACKGROUND

The efficacy of treatment in hemianopic patients to restore missing vision is controversial. So far, successful techniques require laborious stimulus presentation or restrict improvements to selected visual field areas. Due to the large number of brain-damaged patients suffering from visual field defects, there is a need for an efficient automated treatment of the total visual field.

METHODS

A customized treatment was developed for the reaction perimeter, permitting a time-saving adaptive-stimulus presentation under conditions of maximum attention. Twenty hemianopic patients, without visual neglect, were treated twice weekly for an average of 8.2 months starting 24.2 months after the insult. Each treatment session averaged 45 min in duration.

RESULTS

In 17 out of 20 patients a significant and stable increase of the visual field size (average 11.3 degrees +/- 8.1) was observed as well as improvement of the detection rate in the defective visual field (average 18.6% +/- 13.5). A two-factor cluster analysis demonstrated that binocular treatment was in general more effective in augmenting the visual detection rate than monocular. Four out of five patients with a visual field increase larger than 10 degrees suffered from hemorrhage, whereas all seven patients with an increase of 5 degrees or less suffered from infarction. Most patients reported that visual field restoration correlated with improvement of visual-related activities of daily living.

CONCLUSION

Rehabilitation treatment with the Lubeck Reaction Perimeter is a new and efficient method to restore part of the visual field in hemianopia. Since successful transfer of treatment effects to the occluded eye is achieved under monocular treatment conditions, it is hypothesized that the damaged visual cortex itself is the structure in which recovery takes place.

Vision restoration therapy does not benefit from costimulation: A pilot study

Visual field deficits in patients have long been considered to be nontreatable, but in previous studies we have found an enlargement of the intact visual field following vision restoration therapy (VRT). In the present pilot study, we wished to determine whether a double-stimulation approach would facilitate visual field enlargements beyond those achieved by the single-stimulus paradigm used in standard VRT. This was motivated by the findings that following visual cortex injury in animals, the size of receptive fields could be enlarged by systematic costimulation, where two stimuli were used to excite visual cortex neurons (Eysel, Eyding, & Schweigart, 1998). Patients (n = 23) with stable homonymous field deficits after trauma, cerebral ischemia, or hemorrhage (lesion age > 6 months) carried out either (a) standard VRT with a single stimulation (n = 9), or vision therapy with (b) a parallel costimulation (n = 7) or (c) a moving costimulation paradigm (n = 7). Training was carried out twice daily for 30 min over a 3-month period. Before and after therapy, visual fields were tested with 30 degrees and 90 degrees Tübinger automatic perimetry (TAP) and with high-resolution perimetry (HRP). Eye movements were recorded with an eye tracking system. When data of all three types of visual field training were pooled, we found significant improvements of stimulus detection in HRP (4.2%) and fewer misses within the central 30 degrees perimetrically (-3.7% right eye, OD, or -4.4% left eye, OS). However, the type of training did not make any difference such that the three training groups profited equally. A more detailed analysis of trained versus untrained visual field areas in 16 patients revealed a superiority of the trained area of only 1.1% in HRP and between 3.5% (OS) and 4.4% (OD) in TAP. Spatial attention and alertness improved significantly in all three groups and correlated significantly with visual field enlargements. While vision training had no influence on the patient's testimonials concerning their visual abilities, the patients significantly improved in a practical paper-and-pencil number tracking task (Zahlen-Verbindungs Test; ZVT). Visual field enlargement does not benefit from a double-stimulation paradigm, but visual attention seems to play an important role in vision restoration. The improvements in trained as well as in untrained areas are explained by top-down attentional control mechanisms interacting with local visual cortex plasticity.

Capturing the benefit of vision restoration therapy

PURPOSE OF REVIEW

Vision restoration therapy has shown promise as a treatment strategy to improve visual field deficits in patients with lesions of the brain or optic nerve. Objective measures of its efficacy, however, have remained controversial. A review of the current theories supporting the reported benefits of vision restoration therapy, and the dissenting opinions, reconsiders vision restoration therapy as an emerging therapy.

RECENT FINDINGS

The benefits of vision restoration therapy have been challenged by a study suggesting that no improvement exists with careful control of fixation. Alternatively, others suggest that eye movements are not induced by vision restoration therapy. Functional imaging studies demonstrate the potential role of plasticity in vision restoration therapy. While the exact mechanism remains to be elucidated, subjective improvement in daily functioning is reported in a significant percentage of patients.

SUMMARY

Vision restoration therapy is a noninvasive, home-based strategy for the rehabilitation of patients with visual field loss caused by structural or ischemic damage. While subjective benefits in functional status have been reported by patients following completion of the program, debate centers around the inadequacy of the methods used to document its efficacy. Until such a method is validated by carefully controlled studies, subjective improvement in visual function stands alone as evidence of vision restoration therapy's benefit.

Training-induced cortical representation of a hemianopic hemifield

BACKGROUND

Patients with homonymous hemianopia often have some residual sensitivity for visual stimuli in their blind hemifield. Previous imaging studies suggest an important role for extrastriate cortical areas in such residual vision, but results of training to improve vision in patients with hemianopia are conflicting.

OBJECTIVE

To show that intensive training with flicker stimulation in the chronic stage of stroke can reorganise visual cortices of an adult patient.

METHODS

A 61-year-old patient with homonymous hemianopia was trained with flicker stimulation, starting 22 months after stroke. Changes in functioning during training were documented with magnetoencephalography, and the cortical organisation after training was examined with functional magnetic resonance imaging (fMRI).

RESULTS

Both imaging methods showed that, after training, visual information from both hemifields was processed mainly in the intact hemisphere. The fMRI mapping results showed the representations of both the blind and the normal hemifield in the same set of cortical areas in the intact hemisphere, more specifically in the visual motion-sensitive area V5, in a region around the superior temporal sulcus and in retinotopic visual areas V1 (primary visual cortex), V2, V3 and V3a.

CONCLUSIONS

Intensive training of a blind hemifield can induce cortical reorganisation in an adult patient, and this case shows an ipsilateral representation of the trained visual hemifield in several cortical areas, including the primary visual cortex.

Temporal sensitivity in a hemianopic visual field can be improved by long-term training using flicker stimulation

BACKGROUND

Blindness of a visual half-field (hemianopia) is a common symptom after postchiasmatic cerebral lesions. Although hemianopia severely limits activities of daily life, current clinical practice comprises no training of visual functions in the blind hemifield.

OBJECTIVE

To find out whether flicker sensitivity in the blind hemifield can be improved with intensive training, and whether training with flicker stimulation can evoke changes in cortical responsiveness.

METHODS

Two men with homonymous hemianopia participated in the experiments. They trained with flicker stimuli at 30 degrees or with flickering letters at 10 degrees eccentricity twice a week for a year, and continued training with more peripheral stimuli thereafter. Neuromagnetic responses were registered at 1-2-month intervals, and the Goldmann perimetry was recorded before, during and after training.

RESULTS

Flicker sensitivity in the blind hemifield improved to the level of the intact hemifield within 30 degrees eccentricity in one participant and 20 degrees eccentricity in the other. Flickering letters were recognised equally at 10 degrees eccentricity in the blind and intact hemifields. Improvement spread from the stimulated horizontal meridian to the whole hemianopic field within 30 degrees. Before training, neuromagnetic recordings showed no signal above the noise level in the hemianopic side. During training, evoked fields emerged in both participants. No changes were found in the Goldmann perimetry.

DISCUSSION

Results show that sensitivity to flicker could be fully restored in the stimulated region, that improvement in sensitivity spreads to the surrounding neuronal networks, and that, during training, accompanying changes occurred in the neuromagnetic fields.

Recovery of visual field defects: a large clinical observational study using vision restoration therapy

PURPOSE

In small experimental trials, vision restoration therapy (VRT), a home-based rehabilitation method, has shown to enlarge the visual field and improve reaction times in patients with lesion involving the CNS. We now evaluated the outcome of VRT in a large sample of clinical patients and studied factors contributing to subjective and objective measures of visual field alterations.

METHODS

Clinical observational analysis of visual fields of 302 patients before and after being treated with computer-based vision restoration therapy for a period of 6 months at eight clinical centers in central Europe. The visual field defects were due to ischemia, hemorrhage, head trauma, tumor removal or anterior ischemic optic neuropathy. Primary outcome measure was a visual field assessment with super-threshold perimetry. Additionally, conventional near-threshold perimetry, eye movements and subjective reports of daily life activities were assessed in a subset of the patients.

RESULTS

VRT improved patients' ability to detect super-threshold stimuli in the previously deficient area of the visual field by 17.2% and these detection gains were not significantly correlated with eye movements. Notable improvements were seen in 70.9% of the patients. Efficacy was independent of lesion age and etiology, but patients with larger areas of residual vision at baseline and patients>65 years old benefited most. Conventional perimetry validated visual field enlargements and patient testimonials confirmed the improvement in every day visual functions.

CONCLUSIONS

VRT improves visual functions in a large clinical sample of patients with visual field defects involving the CNS, confirming former experimental studies.

NovaVision: vision restoration therapy

PURPOSE OF REVIEW

The aim of this article is to review the controversial findings for NovaVision's vision restoration therapy.

RECENT FINDINGS

It has been claimed that NovaVision's computerized therapy results in expansion of the visual field in optic nerve and occipital lesions, but the outcome has been challenged on the grounds of unsatisfactory perimetric control of central fixation and disputed mechanisms.

SUMMARY

In clinical practice NovaVision's therapy should not currently gain acceptance in view of unacceptable perimetric standards and equivocal results. Possible effects on a relative scotoma at the edge of a lesion have not been adequately explored. In the interim, research should also be focused on compensatory eye movement strategies.

Visual field recovery after vision restoration therapy (VRT) is independent of eye movements: an eye tracker study

AIM

It has been argued that patients with visual field defects compensate for their deficit by making more frequent eye movements toward the hemianopic field and that visual field enlargements found after vision restoration therapy (VRT) may be an artefact of such eye movements. In order to determine if this was correct, we recorded eye movements in hemianopic subjects before and after VRT.

METHODS

Visual fields were measured in subjects with homonymous visual field defects (n=15) caused by trauma, cerebral ischemia or haemorrhage (lesion age >6 months). Visual field charts were plotted using both high-resolution perimetry (HRP) and conventional perimetry before and after a 3-month period of VRT, with eye movements being recorded with a 2D-eye tracker. This permitted quantification of eye positions and measurements of deviation from fixation.

RESULTS

VRT lead to significant visual field enlargements as indicated by an increase of stimulus detection of 3.8% when tested using HRP and about 2.2% (OD) and 3.5% (OS) fewer misses with conventional perimetry. Eye movements were expressed as the standard deviations (S.D.) of the eye position recordings from fixation. Before VRT, the S.D. was +/-0.82 degrees horizontally and +/-1.16 degrees vertically; after VRT, it was +/-0.68 degrees and +/-1.39 degrees , respectively. A cluster analysis of the horizontal eye movements before VRT showed three types of subjects with (i) small (n=7), (ii) medium (n=7) or (iii) large fixation instability (n=1). Saccades were directed equally to the right or the left side; i.e., with no preference toward the blind hemifield. After VRT, many subjects showed a smaller variability of horizontal eye movements. Before VRT, 81.6% of the recorded eye positions were found within a range of 1 degrees horizontally from fixation, whereas after VRT, 88.3% were within that range. In the 2 degrees range, we found 94.8% before and 98.9% after VRT. Subjects moved their eyes 5 degrees or more 0.3% of the time before VRT versus 0.1% after VRT. Thus, in this study, subjects with homonymous visual field defects who were attempting to fixate a central target while their fields were being plotted, typically showed brief horizontal shifts with no preference toward or away from the blind hemifield. These eye movements were usually less than 1 degrees from fixation. Large saccades toward the blind field after VRT were very rare.

CONCLUSION

VRT has no effect on either the direction or the amplitude of horizontal eye movements during visual field testing. These results argue against the theory that the visual field enlargements are artefacts induced by eye movements.

Structural anatomy of pure and hemianopic alexia

BACKGROUND

The two most common types of acquired reading disorder resulting from damage to the territory of the dominant posterior cerebral artery are hemianopic and pure alexia. Patients with pronounced hemianopic alexia have a right homonymous hemianopia that encroaches into central or parafoveal vision; they read individual words well, but generate inefficient reading saccades when reading along a line of text. Patients with pure alexia also often have a hemianopia but are more disabled, making frequent errors on individual words; they have sustained damage to a brain region that supports efficient word identification.

OBJECTIVE

To investigate the differences in lesion site between hemianopic alexia and pure alexia groups, as rehabilitative techniques differ between the two conditions.

METHODS

High-resolution magnetic resonance images were obtained from seven patients with hemianopic alexia and from six patients with pure alexia caused by a left occipital stroke. The boundary of each lesion was defined and lesion volumes were then transformed into a standard stereotactic space so that regional comparisons could be made.

RESULTS

The two patient groups did not differ in terms of damage to the medial left occipital lobe, but those with pure alexia had additional lateral damage to the posterior fusiform gyrus and adjacent tissue.

CONCLUSIONS

Clinicians will be able to predict the type of reading disorder patients with left occipital lesions have from simple tests of reading speed and the distribution of damage to the left occipital lobe on brain imaging. This information will aid management decisions, including recommendations for reading rehabilitation.

Visual restoration in cortical blindness: Insights from natural and TMS-induced blindsight

Unilateral damage to visual cortex of the parietal or occipital lobe can cause the patient to be unaware of contralesional visual information due to either hemispatial neglect or hemianopia. It is now known that both neglect and hemianopia result from the disruption of a dynamic interaction between cortical visual pathways and more phylogenetically primitive visual pathways to the midbrain. We consider the therapeutic implications of these cortical-subcortical interactions in the rehabilitation of hemianopia. We start with the pheonmenon of "blindsight", in which patients with hemianopia can be shown, by implicit measures of visual detection or discrimination, to process visual information without conscious awareness. Some variants of blindsight have been postulated to recruit subcortical processes, while others may reflect compensatory optimisation of processing of spared visual cortex. Both mechanisms may offer opportunities for innovative strategies for rehabilitation of visual field defects. We relate the neural mechanisms that have been proposed to underlie blindsight to those that have been suggested to underlie the recovery of visual function after rehabilitation. It is suggested that the similarity and overlap of the neural processes supporting blindsight and recovery of visual function might provide insights for effective rehabilitation strategies for restoring visual functions.

Effect of visual restitution training on absolute homonymous scotomas

The authors examined 16 patients with stable homonymous visual field defects (HVFDs) with static automated perimetry (SAP). Training effect E was defined as difference of the proportions of absolutely defective locations in all test locations, before and after visual restitution training (VRT). E was 0.05 +/- 0.05 (mean +/- SD). The authors observed a relevant training effect (E >or= 0.12) in two subjects, but only monocularly. VRT has little effect on absolute HVFDs in SAP.

Prism adaptation changes perceptual awareness for chimeric visual objects but not for chimeric faces in spatial neglect after right-hemisphere stroke

Prism adaptation can ameliorate some symptoms of left spatial neglect after right-hemisphere stroke. The mechanisms behind this remain unclear. Prism therapy may increase exploration towards the contralesional side, yet without improving perceptual awareness, as apparently for the left side of chimeric face stimuli (Ferber et al. 2003). However, other prism studies suggest that perceptual awareness might be improved (e.g., Maravita et al., 2003). We tested the impact of prism therapy on visual awareness for the left side of chimeric objects as well as chimeric faces, in three neglect patients. Prism therapy dramatically improved awareness for the identity of the left side of chimeric non-face objects, but had no effect on judging expressions for chimeric faces. The latter may thus be unique in showing no prism benefit.

Vergleich von Früh- und Spätrehabilitation bei zerebral geschädigten Patienten mit Gesichtsfelddefekten

BACKGROUND

Most rehabilitation studies on visual field deficits after stroke or trauma are conducted after completion of the spontaneous recovery phase. However, the question arises whether more extensive visual field improvements can be reached when the training starts very soon after the lesion.

METHODS

In this study, the results of 26 patients who began visual restoration therapy within the first 12 months after the lesion were compared with an age-related group whose lesions were more than 1 year old.

RESULTS

The early-onset group showed an improvement of 8% in computer campimetry and 10-15% in conventional automated perimetry. The late-onset group had 13.5% improvement in campimetry and 20% in perimetry.

CONCLUSION

In contrast to our assumptions, there was no significant difference between the groups. Furthermore, the late-onset group showed considerably greater improvement than the early-onset group. It is proposed that pronounced attention deficits soon after brain damage may complicate the training.

Visual search improvement in hemianopic patients after audio-visual stimulation

One of the most effective techniques in the rehabilitation of visual field defects is based on implementation of oculomotor strategies to compensate for visual field loss. In the present study we develop a new rehabilitation approach based on the audio-visual stimulation of the visual field. Since it has been demonstrated that audio-visual interaction in multisensory neurons can improve temporally visual perception in patients with hemianopia, the aim of the present study was to verify whether a systematic audio-visual stimulation might induce a long-lasting amelioration of visual field disorders. Eight patients with chronic visual field defects were trained to detect the presence of visual targets. During the training, the visual stimulus could be presented alone, i.e. unimodal condition, or together with an acoustic stimulus, i.e. crossmodal conditions. In the crossmodal conditions, the spatial disparity between the visual and the acoustic stimuli were systematically varied (0, 16 and 32 degrees of disparity). Furthermore, the temporal interval between the acoustic stimulus and the visual target in the crossmodal conditions was gradually reduced from 500 to 0 ms. Patients underwent the treatment for 4 h daily, over a period of nearly 2 weeks. The results showed a progressive improvement of visual detections during the training and an improvement of visual oculomotor exploration that allowed patients to efficiently compensate for the loss of vision. More interesting, there was a transfer of treatment gains to functional measures assessing visual field exploration and to daily-life activities, which was found stable at the 1 month follow-up control session. These findings are very promising with respect to the possibility of taking advantage of human multisensory capabilities to recover from unimodal sensory impairments.

Rehabilitation strategies for patients with homonymous visual field defects

Homonymous visual field defects (HVFDs) are among the most common disorders that occur in brain damage, particularly after stroke. They lead to considerable disabilities, particularly with reading and visual exploration. A variety of different approaches, including optical aids and visual training techniques, have been examined for the rehabilitation of these HVFDs. Despite the considerable ingenuity that has been applied and anecdotal evidence that has accumulated, rigorously controlled trials that clearly establish efficacy of any method are lacking.

Does visual restitution training change absolute homonymous visual field defects? A fundus controlled study

AIM

To examine whether visual restitution training (VRT) is able to change absolute homonymous field defect, assessed with fundus controlled microperimetry, in patients with hemianopia.

METHODS

17 patients with stable homonymous visual field defects before and after a 6 month VRT period were investigated with a specialised microperimetric method using a scanning laser ophthalmoscope (SLO). Fixation was controlled by SLO fundus monitoring. The size of the field defect was quantified by calculating the ratio of the number of absolute defects and the number of test points; the training effect E was defined as the difference between these two ratios before and after training. A shift of the entire vertical visual field border by 1 degrees would result in an E value of 0.14.

RESULTS

The mean training effect of all right eyes was E = 0.025 (SD 0.052) and all left eyes E = 0.008 (SD 0.034). In one eye, a slight non-homonymous improvement along the horizontal meridian occurred.

CONCLUSIONS

In one patient, a slight improvement along the horizontal meridian was found in one eye. In none of the patients was an explicit homonymous change of the absolute field defect border observed after training.

Saccadic visual search training: a treatment for patients with homonymous hemianopia

OBJECTIVES

We describe a novel rehabilitation tool for patients with homonymous hemianopia based on a visual search (VS) paradigm that is portable, inexpensive, and easy to deploy. We hypothesised that by training patients to improve the efficiency of eye movements made in their blind field their disability would be alleviated.

METHODS

Twenty nine patients with homonymous visual field defects (HVFD) without neglect practised VS paradigms in 20 daily sessions over one month. Search fields comprising randomly positioned target and distracter elements, differing by a single feature, were displayed for three seconds on a dedicated television monitor in the patients' homes. Improvements were assessed by examining response time (RT), error rates in VS, perimetric visual fields (VFs) and visual search fields (VSFs), before and after treatment. Functional improvements were measured using objective visual tasks which represented activities of daily living (ADL) and a subjective questionnaire.

RESULTS

As a group the patients had significantly shorter mean RT in VS after training (p<0.001) and demonstrated a variety of mechanisms to account for this. Improvements were confined to the training period and maintained at follow up. Three patients had significantly longer RT after training. They had high initial error rates which improved with training. Patients performed ADL tasks significantly faster after training and reported significant subjective improvements. There was no concomitant enlargement of the VF, but there was a small but significant enlargement of the VSF.

CONCLUSION

Patients can improve VS with practice. This usually involves shorter RTs, but occasionally a longer RT in a complex speed-accuracy trade-off. These changes translate to improved overall visual function, assessed objectively and subjectively, suggesting that they represent robust training effects. The underlying mechanism may involve the adoption of compensatory eye movement strategies.

[Visual search training for a case of homonymous field defect with multiple visual dysfunctions]

A 72-year-old right handed man developed right homonymous hemianopia without macular sparing, left homonymous lower quadranopia with macular sparing, cerebral amblyopia, cerebral achromatopsia, impaired form vision, and mild right hemispatial neglect, after multiple cerebral infarctions, involving bilateral occipital cortices. His intelligence and memory were deteriorated moderately. He failed to notice objects located in the affected visual field, because of his severely impaired visual search. When ordinary lighting was used, he showed severe right-sided omissions on the line cancellation test. However, omissions were less marked under the brighter lighting. By using a modified method of Kerkhoff and Vianen (1994), he was trained to make saccadic eye movements toward affected regions to find a target and to search and point at targets arranged randomly. As the sensitivity for contrast of isoluminante red and green stimuli was preserved well at high spatial frequencies despite the decreaced contrast sensitivity for brightness, we used green targets as the training stimuli. After the training, search field and pointing range that could be covered by the patient increased in size for both green and white targets, and daily activities improved. Moreover, after the training, he no longer showed discrepancy in line cancellation performances between ordinary and brighter lighting conditions. In the follow up period, the search field and the performance on the line cancellation test were maintained, while the performance of pointing targets array declined. The family members complained of mild re-deterioration of daily activities. Then, the training for searching and pointing re-introduced at home. After the training, his pointing performance and daily activities, evaluated by questionnaires to his family members, improved again. In conclusion, it was suggested that disordered visual search after a homonymous field defect can be treated effectively, even if multiple visual dysfunctions were associated.

Vision restoration therapy (VRT) efficacy as assessed by comparative perimetric analysis and subjective questionnaires

PURPOSE

We wished to evaluate the efficacy of vision restoration therapy (VRT) in patients with post-chiasmatic brain damage using different functional perimetric tests. These were compared with measures of subjective vision and reaction time.

METHODS

An open trial was conducted with hemianopia/scotoma (n=16) patients. Before and after 6 months of VRT results of high resolution (HRP) and Tuebingen automated perimetry (TAP) were evaluated and compared to performance in a Scanning Laser Ophthalmoscope (SLO) as previously reported. Whereas TAP and HRP used above-threshold or near-threshold individual target stimuli on grey background, the SLO used a psychophysical task of detection of three black targets (reverse stimulus) on bright red, patterned background. Subjective testimonials of activities of daily living (ADL) were probed with questionnaires and interviews.

RESULTS

Before VRT, the visual field border as assessed by SLO was located significantly closer to the vertical midline than the HRP and TAP border (border mismatch). After VRT the SLO border was still unchanged whereas HRP measurements revealed significant border shifts due to improved stimulus detection (p<0.0001) and improved reaction time (p<0.005) . Fewer misses were also observed in both eyes with TAP (p<0.01) which was primarily due to a significant shift of the absolute borders. Thus, VRT potentiated the mismatch between the SLO borders and the HRP/TAP borders. Fixation performance and the blind spot position remained unchanged after VRT. ADL ratings in the questionnaire improved significantly after VRT which was confirmed by independent patient testimonials.

CONCLUSIONS

We replicated earlier findings that VRT improves stimulus detection in HRP and TAP perimetry which were accompanied by subjective, visual improvements. These changes are not caused by fixation or eye movement artifacts. Because the SLO border was located significantly closer to the vertical midline before VRT ("border mismatch") and, in contrast to HRP and TAP, did not change after VRT, we interpret this border mismatch to indicate that the SLO task was too difficult to perform and thus insensitive to VRT effects. Significant reaction time improvements indicate that plasticity of temporal processing might play an important role in vision restoration after brain damage. A further description of the precise psychophysical nature of the restored areas of residual vision is now warranted.

Rehabilitation of chronic post-stroke visual field defect with computer-assisted training: a clinical and neurophysiological study

PURPOSE

Our aim was to study whether homonymous visual field defects could be restored in chronic stroke patients (N = 5) using computer-assisted training, and whether the possible beneficial effect could be maintained. Visual evoked potential (VEP) recordings were applied to evaluate whether they could demonstrate the possible training effects at the cortical level.

METHODS

We applied a specially designed computer program in the training. Subjective assessment, static and kinetic perimetry, and pattern reversal hemifield VEP recordings were used to detect the possible changes.

RESULTS

Two patients showed improvements immediately after the training in static perimetry. Further improvements were detected at a later follow-up in three patients. With kinetic perimetry, improvements were detected in three patients. The visual field defect was detected with VEP recordings in four patients before the training, and improvements could be verified with the method in three patients, two of which clearly improved in the static perimetry as well.

CONCLUSIONS

In three patients, the visual defect diminished with the computer-assisted method. It seems evident that visual field defects resulting from stroke can be partially restored even in the chronic phase.

Visual search and its disorders

PURPOSE OF REVIEW

A greater understanding of the underlying component mechanisms of normal visual search provides explanations for disturbances seen in certain neurological conditions. This review focuses on recent advances in this field which bear on the neurology of visual search in health and disease.

RECENT FINDINGS

Foremost, visual search requires a normal apparatus for the application of attentional resources to the visual environment and, with that facility lost in hemispatial neglect, search becomes uselessly stuck within one portion of the field. New evidence suggests that loss of normal registration of where the eyes have been compounds the problem. Even if attention can be deployed flexibly, its parameters must be chosen strategically, in terms of saccade amplitude, size of attentional window at each fixation and search path taken. Evidence is growing that the prefrontal cortex plays a complex role in this strategic control. Rehabilitation strategies of the future may be tailored according to which component functions have been lost in different patient groups.

SUMMARY

Visual search is a dominant human activity and provides not only a window into how brain function is deranged after structural damage, but also offers the prospect of an ideal modality through which to deliver future behavioural therapies. New techniques have advanced our understanding of the physiology of visual search enormously in the past few decades. The time is now ripe in which to begin to integrate these findings into our understanding of the pathophysiology and treatment prospects of neurological disorders like hemispatial neglect, hemianopia and other deficits after stroke.

Treating with spectacle lenses: a novel idea!?

A design approach to low-vision device development-vision multiplexing-was introduced recently. This approach has been applied successfully to the design of novel electronic and optical low-vision aids. This paper discusses the application of the vision-multiplexing concept to spectacle lens design to address issues of low vision and to resolve problems of color discrimination and glare in driving. Because spectacles are considered a fashion accessory as much as they are a vision aid, cosmetic considerations are critical to the design of such aids. Spectacle-borne devices that are not concealed or attractive are unlikely to be used widely. Efforts to combine the functionality of vision multiplexing with improved appearance are illustrated.