Erich Kasten

Computer-based training for the treatment of partial blindness

Partial blindness after brain injury has been considered non-treatable. To evaluate whether patients with visual-field defects can profit from computer-based visual restitution training (VRT), two independent clinical trials were conducted using patients with optic nerve (n = 19) or post-chiasmatic brain injury (n = 19). In post-chiasma patients, VRT led to a significant improvement (29.4%) over baseline in the ability to detect visual stimuli; in optic nerve patients, the effects were even more pronounced (73.6% improvement). Visual-field enlargements were confirmed by the observation of a visual-field expansion of 4.9°–5.8° of visual angle and improved acuity in optic nerve patients. Ninety five percent of the VRT-treated patients showed improvements, 72.2% confirmed visual improvements subjectively. Patients receiving a placebo training did not show comparable improvements. In conclusion, VRT with a computer program improves vision in patients with visual-field defects and offers a new, cost-effective therapy for partial blindness.

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° 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.

Attentional cueing improves vision restoration therapy in patients with visual field defects

Background: In patients with postgenicular lesions of the visual system, areas of residual vision (ARVs) are the main predictor of recovery induced by vision restoration therapy (VRT). In these partially defective regions, the elevated perceptual thresholds can be acutely reduced by attentional cueing. Objective: To examine whether directing attention to ARVs using a visuospatial cue also increases long-term neural plasticity and thus enhances permanent training outcome. Methods: In a prospective, randomized clinical trial, treatment outcome was compared in patients with postgenicular visual system lesions who received either standard VRT (control group [CG]; n = 10) or VRT with attentional cueing (experimental group [EG]; n = 9). Visual field size was determined before and after a 6-month treatment period using Tübingen Automated Perimetry and computer-based high-resolution perimetry (HRP) and in regular intervals throughout this period by HRP and detection performance in VRT. Results: In the area of the cue, restoration of vision was significantly greater than during VRT without cueing: cued patients showed a much more pronounced shift of the visual field border toward the blind area than that observed in the CG or in uncued regions of the EG. Focusing attention at ARVs during treatment changed topographic and temporal patterns of recovery as compared with uncued regions of the visual field. Conclusions: Use of a visuospatial cue to focus attention at areas of residual vision amplifies long-term neuronal plasticity. The authors propose that top-down signals preactivate partially damaged areas of V1, thus linking visual and attentional neuronal networks, with the effect of permanently increasing conscious visual perception.

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.

Restoration of vision by training of residual functions

A new paradigm emerges: visual field defects after optic nerve or brain injury are partially reversible. Using high-resolution visual field tests, areas of residual vision can be identified which are characterized by impaired vision (relative defect) with some residual capacities. By repetitively stimulating these partially damaged areas with daily computer-based visual restitution training it is now possible to enlarge the visual field. Average border shifts of 5° (range, 0 to 20°) have been found in clinical trials, and training is effective even when started years after the injury. Visual restitution training is useful for the treatment of patients with stroke, head injury, or partial optic nerve damage, as long as the patient presents some residual vision. The improved vision is maintained in most patients after training is discontinued. Brain plasticity is likely to provide the substrate for restoration of vision, opening new opportunities to treat partial blindness, which has been considered irreversible.

Computer-Based Training of Stimulus Detection Improves Color and Simple Pattern Recognition in the Defective Field of Hemianopic Subjects

In a previously conducted randomized placebo-controlled trial, we were able to demonstrate significant visual field enlargement induced by restitution therapy in patients with cerebral lesions [Kasten, E., Wuest, S., Behrens-Bamann, W., & Sabel, B. A. (1998c). Computer-based training for the treatment of partial blindness. Nature Medicine, 4, 1083-1087.]. Visual field training was performed on a computer monitor for 1 hr per day over a period of 6 months. Since the procedure included only stimulation with white light, in the present study we investigated if this simple detection training had a transfer effect on color or form recognition in the trained area (i.e., in the absence of modality specific training). Answering this question would be crucial for planning optimal restitution therapy: In case there is no transfer of training effects to other visual modalities, a specific treatment of each visual function must be performed in order to achieve maximum benefit. Therefore, we analyzed the data from 32 patients with visual field defects who had participated in the original trial and whose form and color recognition had been investigated. The experimental group (n = 19, restitution training) experienced not only an increase of 12.8% correctly detected stimuli (PeriMa program, p < .05), but also an improvement of 5.6% in pattern recognition (PeriForm) and of 6.1% in color perception (PeriColor), respectively. In contrast, the placebo group (n = 13, fixation training) showed no significant changes from baseline to final outcome in any of the visual modalities (PeriMa: 0.3%; PeriForm: -0.3%; PeriColor: 0.4%). Conventional perimetry yielded an increase of 7.8% detected stimuli in the experimental group, but only of 1.2% in the placebo group (p < .05). For form recognition and color perception, the differences between the results of the experimental and the placebo groups narrowly missed significance. However, correlations of diagnostic results showed that mainly those patients who had achieved visual field enlargement also improved in color and form perception: r = .67 (p < .05) between PeriMa and PeriForm and r = .32 between PeriMa and PeriColor. We conclude that visual restitution training using a simple white light stimulus has at least some influence on improving other visual functions such as color and pattern recognition. This result supports the bottleneck theory of visual restitution, i.e., training effects can be explained as a process of perceptual learning and increased processing of information by residual structures surviving lesions of the primary visual pathways.

Programs for diagnosis and therapy of visual field deficits in vision rehabilitation

A suite of computer programs is described for visual field-assessment and training of residual vision in neuropsychological rehabilitation.

Vision restoration therapy after brain damage: Subjective improvements of activities of daily life and their relationship to visual field enlargements

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.1However, 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 perfo...

Stability of Visual Field Enlargements Following Computer-Based Restitution Training - Results of a Follow-up

In a previous randomized placebo-controlled clinical trial, we observed significant visual field enlargements induced by computer-based restitution training in patients with cerebral lesions (Kasten et al., Nature med., 4, 1998, 108387). Now we asked the question whether this effect is stable after training was discontinued Here we report data of a follow-up study after a training-free interval (mean 23.52.3 months after end of therapy). 16 patients of the original restitution group and 6 patients of the placebo group were re-examined. On average, in high resolution computer campimetry (stimulus detection: PeriMa, form recognition: PeriForm, color perception: PeriColor) as well as in conventional automatic perimetry (TAP-2000) both groups showed no significant decline in the number of correctly detected stimuli after training was discontinued. However, cluster analysis revealed three different types of patients, who showed either increase (Type-I), decrease (Type-II) or stability (Type-III) in performance. We propose that many patients learn to use the regained visual capacities not only in the setting of a computer training but also in every day life, while other patients do not use the areas of restored vision and show a decrease of visual functions after the end of training. The Type-I group does not need continuous training, while the Type-II group may benefit from phases of refreshment exercises.

The prevalence rates of refractive errors among children, adolescents, and adults in Germany

Purpose The prevalence rates of myopia vary between 5% in Australian Aborigines to 84% in Hong Kong and Taiwan, 30% in Norwegian adults, and 49.5% in Swedish schoolchildren. The aim of this study was to determine the prevalence of refractive errors in German children, adolescents, and adults. Methods The parents (aged 24–65 years) and their children (516 subjects aged 2–35 years) were asked to fill out a questionnaire about their refractive error and spectacle use. Emmetropia was defined as refractive status between +0.25D and −0.25D. Myopia was characterized as ≤−0.5D and hyperopia as ≥+0.5D. All information concerning refractive error were controlled by asking their opticians. Results The prevalence rates of myopia differed significantly between all investigated age groups: it was 0% in children aged 2–6 years, 5.5% in children aged 7–11 years, 21.0% in adolescents (aged 12–17 years) and 41.3% in adults aged 18–35 years (Pearson’s Chi-square, p = 0.000). Furthermore, 9.8% of children aged 2–6 years were hyperopic, 6.4% of children aged 7–11 years, 3.7% of adolescents, and 2.9% of adults (p = 0.380). The prevalence of myopia in females (23.6%) was significantly higher than in males (14.6%, p = 0.018). The difference between the self-reported and the refractive error reported by their opticians was very small and was not significant (p = 0.850). Conclusion In Germany, the prevalence of myopia seems to be somewhat lower than in Asia and Europe. There are few comparable studies concerning the prevalence rates of hyperopia.