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The topography of training-induced visual field recovery: Perimetric maps and subjective representations
Abstract
The cognitive representation of blind regions varies considerably between patients with vision loss and may influence compensatory behaviour and treatment motivation. We therefore measured “objective” visual field topography (perimetry) in 19 patients with postgeniculate visual system lesions and related this to the subjective scotoma representation as expressed by patients’ drawings of the defect and monitored changes of these measures during training-induced recovery of function. Blind regions were mostly adequately represented; however, central regions were overestimated and peripheral areas underestimated in size. Perimetric and subjective defect size decreased significantly during training. Again, training-induced visual field border shifts in central regions were larger in subjective than in perimetric maps but vice versa in the peripheral field. Thus, vision restoration therapy improves “objective” visual field size along with its cognitive representation. The subjective topography is shaped by the functional importance of visual field regions and is a function of cortical magnification, thus resembling the neural representation in visual cortex.
... VRT training has been described in detail elsewhere. 31 Briefly, participants were seated in front of a computer screen at a constant viewing distance and instructed to detect (signaled by a key press) the presence of a flashed light stimulus while maintaining fixation on a central target. Built-in fixation monitoring required patients to respond to a color change of the central fixation target occurring at random intervals. ...
... Frederick, Maryland). 31 To evaluate the effect of the intervention on activities of daily living (ADLs) and quality of life (QOL), 2 validated questionnaires were used: the Veterans Affairs Low Vision-Visual Functional Questionnaire (LV-VFQ) and the Impact of Vision Impairment (IVI) profile. The LV-VFQ assesses an individual's visual ability to perform ADLs across 4 domains, including reading, mobility, visual motor function, and visual processing, 35 whereas the IVI measures the impact of visual impairments on QOL and participation, including access to information, mobility and independence, and emotional well-being. ...
... Previous studies of VRT describe a similar disconnect between changes in objective measures and patients' own subjective impressions of improvement. 24,31,39 This apparent mismatch may be explained by differences in the functional relevance ascribed to different regions of the field (eg, perifoveal vs peripheral) and the degree of awareness of the field deficit. 31 It should be noted, however, that the mismatch of subjective and objective findings may also have emerged from methdological factors such as sampling errors related to the relativley small sample size in the study. ...
Vision Restoration Therapy (VRT) aims to improve visual field function by systematically training regions of residual vision associated with the activity of suboptimal firing neurons within the occipital cortex. Transcranial direct current stimulation (tDCS) has been shown to modulate cortical excitability.
Assess the possible efficacy of tDCS combined with VRT.
The authors conducted a randomized, double-blind, demonstration-of-concept pilot study where participants were assigned to either VRT and tDCS or VRT and sham. The anode was placed over the occipital pole to target both affected and unaffected lobes. One hour training sessions were carried out 3 times per week for 3 months in a laboratory. Outcome measures included objective and subjective changes in visual field, recording of visual fixation performance, and vision-related activities of daily living (ADLs) and quality of life (QOL).
Although 12 participants were enrolled, only 8 could be analyzed. The VRT and tDCS group demonstrated significantly greater expansion in visual field and improvement on ADLs compared with the VRT and sham group. Contrary to expectations, subjective perception of visual field change was greater in the VRT and sham group. QOL did not change for either group. The observed changes in visual field were unrelated to compensatory eye movements, as shown with fixation monitoring.
The combination of occipital cortical tDCS with visual field rehabilitation appears to enhance visual functional outcomes compared with visual rehabilitation alone. TDCS may enhance inherent mechanisms of plasticity associated with training.
... We followed a purely descriptive approach with respect to the subjective data and refrained from interpretation as far as possible. Additionally, subjects were asked to create drawings of their visual field defect in a standard template depicting the visual fields of the right and left eye before and after training (see Poggel, 2002; Poggel et al., 2007 ). Data from the interview were analyzed qualitatively and categorized, and the frequency of selected answers was counted (e.g. the number of patients indicating that training had been helpful) to obtain quantitative data for further statistical analysis. ...
... However, quantitative measures of visual field size did not always correspond with the subjective statements the patients made. Closer analysis showed that the evaluation of improvement depended on the location of visual field increase: even small shifts of the visual field border in the centre were experienced as a large benefit, but shifts of equal or even greater size in the periphery of the visual field remained unnoticed (see Poggel, 2002; Poggel et al., 2007). From the patients' perspective, the training had beneficial effects on everyday life (as indicated by their statements in the post-treatment interviews). ...
... Those patients who had regained so much of their visual field that they were able to notice a difference to the pre-training status were also able to draw the location of improvement with relatively high topographical exactness, although central parts which recovered were somewhat larger in the subjective representation of change than in " reality " (i.e. perimetric measurements; see Poggel et al., 2007). ...
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.
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.
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.
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.
... 60 In another study among a relatively small group of patients (n ¼ 89) with posterior cerebral artery stroke, 54% had hemianopias. 135 Stavern 4,9,18,24,29,37,38,43,44,45,46,47,48,49,53,54,55,58,64,70,79,81,82,85,95,99,101,105,109,117,119,120,134,136,140,141,144,148,149,150,154,155,157,163,172,177,180,183,187,189,192,195,196,197,198,203,204,205,206,215,217,218,222,223,224,225,226,227,231,228,232,233 Side of Field Defect 58 (32) 2, 3, 13,14,20,21,22,23,32,33,34,37,42,44,47,49,58,63,69,89,91,94,98,99,106,107,109,120,121,131,139,140,144,149,154,157,163,173,179,181,187,189,190,191,192,195,196,203,205,209,217 148,154,183,186,189,192,195,196,198,203,204,205,209,210,215,217,223 105,111,120,121,126,136,139,140,149,154,163,180,181,189,191,192,195,196,198,206,209,215,217,221,224,225 ...
... 46 75,162,167 or to an improvement of visual motion perception, 66 Poggel et al 153 found that older patients improved significantly more with regard to visual field size, form recognition, and color discrimination compared with younger patients. Time since lesion was not found to influence the effect of restorative training on visual field gain 66,78,153,155,162,167 or on the improvement in color and form perception. 153 These studies almost exclusively examined patients in the chronic phase with a considerable variation in time since lesion. 90 122 patients with HFVD followed a systematic scanning training. ...
Homonymous visual field defects (HVFDs) are a common consequence of posterior brain injury. Most patients do not recover spontaneously and require rehabiliation. To determine whether a certain intervention may help an individual patient, it is necessary to predict the patient's level of functioning and the effect of specific training. We provide an overview of both the existing literature on HVFDs in terms of the International Classification of Functioning, Disability, and Health (ICF) components and the variables predicting the functioning of HVFD patients or the effect of treatment. We systematically analyzed 221 publications on HVFD. All variables included in these articles were classified according to the ICF, as developed by the World Health Organization, and checked for their predictive value. We found that ICF helps to clarify the scope of the existing literature and provides a framework for designing future studies, which should consider including more outcome measures related to Activities and Participation. Although several factors have been described that predict HVFD patients' level of functioning or the effects of training, additional research is necessary to identify more.
... • Subjective drawings of the affected hemifield: To characterize a subjective visual field, the patients were instructed to fixate on a central target on a 9 ϫ 12-in sheet of graph paper (similar in design to an Amsler grid) at a viewing distance of 40 cm. The patients then indicated the location of the intact visual border, and the drawings were then digitized and converted into dichotomous black and white figures with preserved aspect ratio [62]. The area of affected vision (represented by regions in black on digital images) was then calculated by using customized software (version 4.0.2; ...
... It is interesting to note that both patients reported that their tDCS status (ie, real or sham) was opposite to what they actually received. Therefore, this disconnect may be related to their own expectations of outcome, or may reflect subjective differences in the functional relevance afforded to different regions of the visual field (eg, central visual versus peripheral sparing) [62]. Certainly, this issue confirms the need for accurate and reliable methods to assess visual function and the value of incorporating experimental blinding to help validate findings. ...
To standardize a protocol for promoting visual rehabilitative outcomes in post-stroke hemianopia by combining occipital cortical transcranial direct current stimulation (tDCS) with Vision Restoration Therapy (VRT).
A comparative case study assessing feasibility and safety.
A controlled laboratory setting.
Two patients, both with right hemianopia after occipital stroke damage. METHODS AND OUTCOME MEASUREMENTS: Both patients underwent an identical VRT protocol that lasted 3 months (30 minutes, twice a day, 3 days per week). In patient 1, anodal tDCS was delivered to the occipital cortex during VRT training, whereas in patient 2 sham tDCS with VRT was performed. The primary outcome, visual field border, was defined objectively by using high-resolution perimetry. Secondary outcomes included subjective characterization of visual deficit and functional surveys that assessed performance on activities of daily living. For patient 1, the neural correlates of visual recovery were also investigated, by using functional magnetic resonance imaging.
Delivery of combined tDCS with VRT was feasible and safe. High-resolution perimetry revealed a greater shift in visual field border for patient 1 versus patient 2. Patient 1 also showed greater recovery of function in activities of daily living. Contrary to the expectation, patient 2 perceived greater subjective improvement in visual field despite objective high-resolution perimetry results that indicated otherwise. In patient 1, visual function recovery was associated with functional magnetic resonance imaging activity in surviving peri-lesional and bilateral higher-order visual areas.
Results of preliminary case comparisons suggest that occipital cortical tDCS may enhance recovery of visual function associated with concurrent VRT through visual cortical reorganization. Future studies may benefit from incorporating protocol refinements such as those described here, which include global capture of function, control for potential confounds, and investigation of underlying neural substrates of recovery.
... Over the past two decades, a number of restitution techniques based on systematic stimulation have been developed. These include utilising repeated stimulation of the light flux channel in Vision Restoration Therapy (Kasten & Sabel, 1995;Poggel, Mueller-Oehring, Kasten, Bunzenthal, & Sabel, 2008;Romano, Schulz, Kenkel, & Todd, 2008). Active stimulation of motion sensitivity (Huxlin et al., 2009), spatial vision (Sahraie et al., 2006) and flicker sensitivity (Raninen, Vanni, Hyv€ arinen, & N€ as€ anen, 2007) have also been used in restoration approaches. ...
Compensatory approaches to rehabilitation of vision loss as a result of brain injury are aimed at improving the efficacy of eye movements, enabling patients to bring the otherwise unseen stimuli into their sighted field. Eye movement training has shown promise in a large number of studies in small clinical populations nevertheless, there remain two problems; standardisation and wide accessibility. NeuroEyeCoach™ (NEC) has been developed to address both. The therapy is based on the visual search approach and is adaptive to the patient's level of disability and the task difficulty is varied systematically through a combination of set-size and target/distractor similarity. Importantly, the therapy can be accessed online or in clinical settings, to enhance accessibility. Here we have reported on the findings from the first 296 consecutive cases who have accessed and completed NEC online, the largest cohort of patients studied to date. Patients' performance on two objective (visual search times and errors) and one subjective (self-reported disability) measures of performance were assessed before and after therapy. The findings showed that patients improved in search time, had less errors and improved disability scores in 87% (255/294), 80% (236/294) and 66% (167/254) of all cases respectively. We examined factors age, sex, side of blindness, age at the onset of brain injury, and time elapsed between the brain injury and start of therapy as predictors of both objective and subjective measures of improvements. Age was a significant predictor of improved search errors with older patients showing larger improvements. Time between brain injury and intervention negatively influenced search reaction time, however, none of the factors could predict improved subjective reports of disability.
... Therefore, foveal vision provides for a much higher visual resolution than peripheral vision. This means that a VFE near the fovea is much more striking or conspicuous than a VFE of the same size in the peripheral visual field (Poggel et al., 2007). Expressing VFE in terms of an average border shift (in degrees) does not make a distinction between possible different eccentricities at which VFE occurred. ...
Visual Restorative function training aims to decrease visual field defect size after acquired brain damage. Some chronic stroke patients regain permission to drive a car after training. This points to a concomitant change in oculomotor behavior, because visual field enlargement is hardly ever large enough for legal driving. This study investigated vRFT-induced changes in oculomotor behavior, using a driving simulator.
Driving performance and oculomotor behavior were measured before and after training in 6 hemianopia patients who had trained 65 hours with vRFT on a PC at home.
Two patients showed negligible visual field enlargement (VFE) and four showed moderate to substantial VFE. Because less visual cortex is devoted to the processing of peripheral than central visual field the same VFE corresponds to less functional restoration of cortex when the defect is at high eccentricity. When this is taken into account, then precisely the two patients that showed the largest cortical gains made significantly more eye movements in the direction of their visual field defect after training.
vRFT with mandatory eye fixation can result in increased eye movement behavior towards the defect. Our study suggests that a threshold amount of cortical functional restoration is required for this effect.
Hemianopia poses significant challenges and requires effective rehabilitation strategies. Traditional visual restoration methods have focused on low-level vision therapies in controlled environments. This paper proposes the integration of natural and ecologically valid environments, e.g., virtual reality (VR), three-dimensional (3D) settings, and cognitive interactions for visual rehabilitation. We review various studies that employed common practices in laboratory or controlled settings. We also discuss the disadvantages of traditional techniques and advocate for a comprehensive and ecological framework in visual rehabilitation. Instead of correcting visual inputs, we emphasize training the visual system to adapt and restore functionality in real-world contexts. By combining real-world environments and higher-level vision approaches, we can enhance visual recovery, improve daily functioning, and restore the quality of life for individuals with visual field defects. Moreover, we stress the importance of incorporating natural environments, VR, 3D settings, and cognitive interactions to maximize the effectiveness of visual rehabilitation and empower patients to regain their visual abilities in real-world scenarios. Continued research and development in this field are crucial to refine and expand the application of these innovative techniques, ultimately enhancing the lives of individuals affected by visual field defects
To determine the relationship of objective and subjective outcome measures of Vision Restoration Training (VRT) for visual field recovery in partially blind patients. This is of interest because the patient's subjective improvement cannot be inferred from objective changes in visual field charts.
Nineteen patients with visual system lesions underwent visual field tests (objective measure) before and after six months of VRT. Subjective outcome was determined by pre- and post-training interviews (open narration, questions on activities of daily living, ratings). Interview content was quantified by determining the response frequency for relevant content categories. Drawings of perceived visual field size were used as a subjective topographical measure. Subjective training results were compared to objective visual field size (perimetry).
Visual field size increased significantly over the training period. Patients' subjective evaluations depended on the size and location of regained areas, but also on specific evaluation of safe navigation, mobility, reading, and communication. Patients with objective increase of visual field size also reported subjective improvements in daily life.
Computer-based training can improve visual field size as well as subjective visual performance. The patients' subjective experience should be included in treatment evaluation to ensure the meaningfulness of training beyond perimetric measures.
Patients with visual field deficits following stroke or neurotrauma can use vision restoration therapy (VRT) to increase their visual field size by about 5° of visual angle.1 However, little is known about whether such visual field enlargements are relevant to visually guided activities of daily life. Specifically, we wish to know (1) if VRT affects activities of daily life (ADL) measures, and (2) to what extent any subjective changes correlate with quantitative measures of visual field enlargements. A retrospective analysis was carried out with data of 69 patients that had been interviewed after 6 months of VRT. Patient testimonials were analyzed post hoc and correlated with demographic status and pre/post VRT changes as measured by perimetric testing. As previously described,VRT significantly increased detection ability and most patients (88%) reported subjective benefits in ADL. A correlation analysis of quantitative parameters of visual field enlargements with subjective patient testimonials was performed. Significant correlation was found in the categories ‘carrying out hobbies’ (r = 0.360) and for ‘general improvement of vision’ (r = 0.244). A trend was
evident for the category ‘reading’ (r = 0.215). No correlation was found between visual field size improvements and ‘visual confidence/ mobility’ and ‘ability to avoid collisions.’ Thus, visual field size appears
only to be one, surprisingly minor, factor among others (such as temporal processing) determining subjective vision in brain damaged patients.
Patients with postchiasmatic visual field defects were trained at the border of their visual field. Using a psychophysical method, light-difference thresholds were determined repeatedly in this visual field area. Improvement in contrast sensitivity and increase in size of the visual field could be obtained by this training procedure. The improvement was confined to the trained visual field area and showed interocular transfer indicating its central nature. Althoughh only contrast sensitivity was trained, the observed improvement was not limited to this visual function. Visual acutity, critical flicker fusion, and colour perception also showed and improvement suggesting an association of these functions. The improvement was restricted to the training period-no spontaneous recovery was observed between or after the periods of training. It is suggested that a lesion in the central visual system does not always result in a complete and permanent loss of function. The critical level of function that normally has to be reached for sufficient neuronal sensitivity may be obtained by systematic visual stimulation in the area between the intact and blind parts of the visual field. This increase in neuronal sensitivity leads to an improvement in visual performance.
From the earliest days of academic psychology, the role of attention in perception has been one of the major foci of research and cognitive modelling (see Yantis1, William James 2). Many experiments with normally-sighted subjects have shown that attention can facilitate (visual) perception (see for example Parasuraman 3). Attended stimuli are more easily detected, reaction time is generally faster than to unattended items in a visual display, and discrimination of similar stimuli is also facilitated 4,5,6. Thus, results from a large number of behavioural studies as well as physiological and imaging experiments in humans and animals indicate that perceptual thresholds are reduced by focusing attention at a certain class of stimuli. Moreover, attention seems to exert its beneficial influence especially when perception is difficult for the individual. Ambiguous or unclear perceptual conditions may occur for different reasons: On the one hand, they may be caused by unfavourable physical stimulus characteristics, e.g. a low contrast of stimulus and background. On the other hand, they may be originating in lesions of the brain affecting the visual system and hence leading to visual field defects. In both cases, allocating attentional resources to a specific area of the visual field should improve perception.
Severe brain injury with bioccipital lesions can lead to 'cortical blindness'. Because there is no established therapy for this syndrome we developed an experimental visual stimulation therapy. We performed this computer-based therapy with an individually increasing severity of the visual tasks over several months. The cortical blind patients treated with this method showed marked restitution of their vision and developed a limited but stable visual field. Focussing the attention of the patients on the specific visual task had a main influence on the therapeutic progress. A reorganization of the visual cortex similar to the findings reported from the sensorimotor cortex might be the basis for this therapeutic success. A repetitive visual stimulation therapy can restore visual function in posttraumatic cortical blind patients and so improve their quality of life.
• We have tested the accuracy of Gordon Holmes' retinotopic map of human striate cortex by correlating magnetic resonance scans with homonymous field defects in patients with clearly defined occipital lobe lesions. Our findings indicate that Holmes underestimated the cortical magnification of central vision. In a revised map of the human striate cortex, we expand the area subserving central vision and reduce the area devoted to peripheral vision. These changes bring the map of human striate cortex into agreement with data reported for closely related nonhuman primate species.
It has recently been shown that, contrary to long-held beliefs, sensory and motor maps are not stable in the adult cerebral cortex. Alteration of input from the periphery results in changes in topography in the cortex, including the primary visual cortex. Mechanisms involved consist mainly of reshaping the receptive field of cortical cells and increasing the sensitivity of deprived cells in the visual cortex. Cortical plasticity allows the brain to adapt to background modifications or to damage of the nervous system. It also underlies learning and attention processes. Cortical changes occurring after focal visual differentiation modify visual perception by filling in visual field defects with information from the area surrounding the scotoma. This modification causes affected subjects to ignore or underestimate their defects. With visual field defects, cortical plasticity also causes distortion in spatial perception. Although the effects of cortical plasticity are prominent in neuro-ophthalmological daily practice, they are usually unrecognized or greatly underestimated. These effects cause delay in recognizing visual field defects, and hence in receiving therapy, while affecting the results of some procedures for testing the visual field. Affected individuals who are unaware of their defects may have increased difficulty in coping with activities in everyday life. Up to now, phenomena related to plasticity in the visual system have been investigated mainly by psychophysicists and neurophysiologists. It is essential to start considering the various effects of cortical reorganization in clinical practice. It is especially important to introduce into clinics the concept of dissociation between actual and perceived defects in the visual field, resulting from the filling-in process, and the need to measure it. This dissociation should also be demonstrated to the affected subjects.
Patienten, die umschriebene Gesichtsfeldausfälle haben, können diese wahrnehmen, wenn sie auf eine mit kleinem Korn in hoher Frequenz flimmernde Heil-Dunkelfläche blicken, ähnlich dem Rauschfeld eines eingeschalteten Fernsehempfängers nach Ende des Programmes. Diese Skotomselbstwahrnehmung kann als Screening-Methode benutzt werden, um anschließend auf demselben Monitor eine manuelle oder automatische Rasterperimetrie gezielt nur im geschädigten Gesichtsfeldbereich durchzuführen. Es werden die Gesichtsfeldergebnisse der Rauschfeldskotometrie von 161 Patienten gezeigt. Offenbar spielen dabei supragenikulär bedingte homonyme Hemianopsien eine Sonderrolle, denn sie werden von den Patienten im Rauschfeld gar nicht oder nur in sehr viel geringerer Ausdehnung wahrgenommen. Auch werden der blinde Fleck und einige angeborene Gesichtsfeldausfälle im Rauschfeld nicht als Ausfall gesehen. - Alle erworbenen umschriebenen Ausfälle, die durch Läsion im 1., 2. oder 3. Neuron entstanden sind, werden dagegen gut im Rauschfeld gesehen, wenn der Patient in der Lage ist, ruhig zu fixieren.
Summary
Patients with circumscribed visual field defects can perceive them while looking at a surface with small black and white spots flickering randomly at high frequency (such as the white-noise field of a TV screen following the end of transmissions for the day). This autonomous perception of scotomata can be used as a screening method, to perform subsequent manual or automatic grid perimetry with the same TV monitor, concentrating on the defective part of the visual field alone. The results of white-noise scotometry used to examine the visual fields of 161 patients are presented. It appears that the test is capable of identifying suprageniculate homonymous hemianopias, since patients either do not observe them at all in the white-noise field or only to a far lesser degree. In addition, the blind spot and some congenital visual field defects are not observed as visual field defects at all in the white-noise field. However, all acquired circumscribed defects caused by lesions of the first, second, or third neuron are readily seen in the white-noise field if the patient is capable of stable fixation.
We have tested the accuracy of Gordon Holmes' retinotopic map of human striate cortex by correlating magnetic resonance scans with homonymous field defects in patients with clearly defined occipital lobe lesions. Our findings indicate that Holmes underestimated the cortical magnification of central vision. In a revised map of the human striate cortex, we expand the area subserving central vision and reduce the area devoted to peripheral vision. These changes bring the map of human striate cortex into agreement with data reported for closely related nonhuman primate species.
This report summarizes the behavioural effects of a right occipital stroke in the author. An upper left quandrantanopia resolved over the first 50 poststroke days to leave a scotoma that included the left upper quadrant of the fovea and extended upwards about 6 degrees and lateral about 15 degrees. There was no further reduction in size over the next 4 years. In the early stages of recovery there was an inability to detect consciously either the presence of objects or their motion, except upon reflection once an object entered the intact visual field. This has been referred to previously as blindsight. On about the fourth day poststroke, part of the scotoma became visually active, producing a scintillating aura, which remains. Shortly thereafter colour perception returned in the scotoma, as did motion detection. Although there was little additional change in the field defect after 2 months, the author's visual abilities have continued to improve, in large part because of a shift in fixation such that information at the centre of the visual field now falls about 1.5 degrees into the lower right portion of the fovea. The implications of the visual and behavioural changes are discussed in the context of multiple visual systems and with respect to recovery of function.