Biomedical subjects

Erich Kasten

Publications and source records attributed to Erich Kasten.

7 recordsLinked to original sources

PubMed2006

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.

Adult↗

PubMed2006

Improving residual vision by attentional cueing in patients with brain lesions.

Visual attention is crucial for almost all processes of visual perception, particularly when perception is difficult. We were interested in the effects of cueing spatial attention in patients with cerebral lesions who face difficulties in visual perception in areas of residual vision at the border of visual field defects. In 23 patients with visual field loss due to post-geniculate brain lesions, stimulus detection performance and reaction times were mapped with high-resolution computer-based perimetry. A cueing procedure using Gestalt completion to attract attention to areas of residual vision was implemented in this test and performance compared in attended and unattended conditions. Stimulus detection and reaction times in areas of residual vision improved significantly under attended conditions. The extent of this effect depended on the size of areas of residual vision within the cued field. Unexpectedly, facilitation was also observed, though to a lesser extent, in invalid cueing conditions, suggesting an unspecific increase of alertness in unattended areas. Our findings show that top-down influences are relevant for visual field testing. Visuo-spatial attention may change patterns of neural activation and induce short-term plasticity not only in the intact visual system but also in the presence of visual field loss after brain lesions. Attentional cueing induces a co-activation of the lesioned visual system and (intact) attentional networks in the brain inducing immediate facilitation of visual perception. This effect may be relevant for designing new strategies to permanently improve vision during neuropsychological rehabilitation.

Adult↗

PubMed2006

A mirror in the mind: a case of visual allaesthesia in homonymous hemianopia.

We report the case of a 61-year-old female patient with intracranial bleeding in left parietal and parieto-temporal regions and a history of epilepsy and migraine. MR images showed lesions of the optic radiation, but primary visual cortical areas were intact. Perimetric testing revealed an incomplete right hemianopia. The patient claimed that visual percepts from her intact field were projected as "mirror images" into the hemianopic field. The illusory images were weak and sometimes difficult to detect, but focusing spatial attention on the "mirror" image increased its saliency. Drawings the patient made of her pseudo-hallucinations revealed that the illusions were lateral transpositions instead of mirror images of real objects. The illusions were tilted in clockwise direction and were never colored, although color discrimination was unimpaired in the patient's left hemifield. We quantified the characteristics of the pseudohallucinations in several experiments: The patient was asked to adjust the position, rotation angle, and size of a white test card in her blind field so that it corresponded with the illusory projection of a card of standard size and position that was presented in the intact field. The test card was compressed in horizontal size by 20% and positioned 17 degrees visual angle to the right of the standard, shifted 1.5 degrees upward or downward, and rotated in clockwise direction by 22.6 degrees on average. Large objects in the intact field were projected incompletely into the blind area. Our patient's symptoms are similar to those reported in earlier case studies of visual allaesthesia. We hypothesize that the "mirror image" is induced by sparse input from contralesional V1 via the corpus callosum upstream of the lesion site and a lack of inhibition or hyperexcitability of ipsilesional early visual areas after deafferentation. The rotation of the illusions may be induced by the parietal lesions causing faulty co-ordinate computations, e.g., an inability to integrate visual and otholitic input.

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PubMed2004

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 Tubingen 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.

Adult↗

PubMed2004

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.

Adult↗

PubMed2003

Neglect and hemianopia superimposed.

In patients with posterior-parietal brain damage it is often difficult to decide whether left-sided omissions in perimetry are due to primary visual loss or due to visual neglect. We investigated 11 patients with combined neglect/hemianopia and 11 patients with pure hemianopia using a visual search task with single or double stimulation conditions. The second stimulus was either the fixation point itself (like in perimetry) or a distractor appearing in the hemifield opposite to the target. The fixation point did not worsen left-sided perception, but its disappearance led to a bias of exploration towards the right side in neglect patients but not in pure hemianopics. A distractor in the intact hemifield worsened the performance to left-sided stimuli, that is, neglect patients behaved as if they were completely hemianopic, even in intact parts of the visual field (VF). Three of the neglect patients showed unconscious processing of the distractor in the left VF, suggesting that the visual field defect was produced by neglect mechanisms rather than primary visual loss. This visual search paradigm appears to be helpful in understanding of the nature of hemianopia versus neglect deficits in individual patients.

Adult↗

PubMed2002

Blindsight after optic nerve injury indicates functionality of spared fibers.

Some patients with lesions in the geniculostriate pathway (GSP) can respond to visual stimuli in the blind field without conscious acknowledgement. The substrate for this "blindsight" is controversial: whether it is the uninjured extrastriate pathway (EXP), which bypasses the lesion site, or residual fibers within damaged visual cortex ("islands of vision"). Using stimulus detection, localization, and spatial summation tasks, we have found blindsight in patients with damage both in the optic nerve (ON) and EXP. The prevalence and functional characteristics of their blindsight are indistinguishable from that in patients with GSP lesions, so blindsight does not require a completely intact EXP. The present findings support the view that a few surviving ON axons within an area of primary damage are sufficient to mediate blindsight: Several combinations of partially intact pathways can transmit information to the extrastriate cortex and the sum of activation of all visual fibers surviving the injury determines if and to what extent blindsight occurs.

Adult↗