Restorative Neurology and Neuroscience - Volume 15, issue 2-3

Authors: Innocenti, Giorgio M. | Kiper, Daniel C. | Knyazeva, Maria G. | Deonna, Thierry W.

Article Type: Research Article

Abstract: MS is a little girl who suffered severe, bilateral destruction of her primary visual areas at six weeks, after premature birth at 30 weeks. Between the ages of 4.5 and 5.5 years she partially recovered different aspects of visual function, and, in particular, the ability to segregate fig-ures from background, based on texture cues. The recovery might have been due to the compensatory role of the remaining visual areas that could have acquired response properties similar …to those of the primary visual areas. This is not supported by the available FMRI (functional magnetic resonance imaging) responses to visual stimuli. Instead, abnormalities in the pattern of stimulus-induced changes of interhemi-spheric EEG-coherence in this patient suggest that her visual callosal connections, and possibly other cortico-cortical connections have re-organized abnormally. Since cortico-cortical connections, including the callosal ones appear to be involved in perceptual binding and figure-background segregation, their reorganization could be an important element in the functional recovery after early lesion, and/or in the residual perceptual impairment. Show more

Keywords: Visual cortex, human, cat, ferret, corpus callosum, connections

Citation: Restorative Neurology and Neuroscience, vol. 15, no. 2-3, pp. 219-227, 1999

Authors: Werth, R. | Moehrenschlager, M.

Article Type: Research Article

Abstract: Sixteen children aged 1 to 15 years who were blind due to an ischemic postgeniculate cerebral lesion after perinatal asphyxia and 6 children aged 1 to 13 years who were blinded after a postgeniculate traumatic cerebral lesion participated in a systematic visual field training. Thirty-one children who were blind due to a postgeniculate lesion following perinatal asphyxia and 12 children who suffered from blindness after a traumatic postgeniculate lesion served as controls. These children received no …visual field training or an ineffective visual field training. The extension of the functional visual field and the functional luminance difference threshold were assessed with a specially designed arc perime-ter. In all children blindness had already persisted for at least one year. Visual functions developed within a training period of three months in 15 of 22 children who received visual field training whereas there was no spontaneous recovery in the control group. The functional luminance difference threshold was still elevated above normal in the case of 5 children who recovered from blindness. In 2 children the latency of sac-cades elicited by light targets in the formerly blind visual area was significantly longer than the latency of saccades elicited by targets in the normal area of the visual field. Light scatter was controlled in order to exclude that the widening of the visual field during training which we interpreted as a sign of the development of visual functions was an effect of scattering light. The findings support the assumption that system-atic stimulation of cerebrally blind areas may facilitate the development of visual functions in brain damaged children. The cerebral lesions associated with the impaired visual functions which improved during the treatment are in agreement with the assumption that spared tissue in the striate and extrastriate visual cortex and underlying white matter is the anatomical basis of the shrinkage of the blind areas. Show more

Keywords: Visual plasticity, brain damage, infancy, visual field training, perimetry, homonymous visual field defect

Citation: Restorative Neurology and Neuroscience, vol. 15, no. 2-3, pp. 229-241, 1999

Authors: Wessinger, C. Mark | Fendrich, Robert | Gazzaniga, Michael S.

Article Type: Research Article

Abstract: Using stabilized visual field mapping techniques, seven hemianopic subjects were extensively investigated for residual visual abilities. Iso-lated islands of detection abilities were demonstrated by four of these subjects. Additional abilities demonstrated within these islands included saccadic and verbal localization, wavelength discrimination, form discrimination, and motion detection. These abilities were also accompanied by low-confidence ratings, and thus have the character of blindsight. It is noteworthy that different subjects demonstrated different abilities at different …visual field locations, underscoring the between and within subject variability often observed with blindsight. Furthermore, magnetic resonance images obtained for each subject demonstrated variable sparing of occipital cortex. Such cortical sparing, in conjunction with the behavioral variability, supports the notion that some instances of blindsight are mediated by remnants of the primary visual pathway. Show more

Keywords: Blindsight, hemianopia, stabilized visual field mapping, residual vision, islands of vision

Citation: Restorative Neurology and Neuroscience, vol. 15, no. 2-3, pp. 243-253, 1999

Authors: Kerkhoff, Georg

Article Type: Research Article

Abstract: In the first part of this review, different types of homonymous Visual Field Disorders (VFDs) and their resulting visual disabilities are ana-lyzed in 313 patients with VFDs and 141 patients without VFDs from a neurorehabilitation centre for adults. Homonymous hemianopia was the most frequent visual field loss (54.7 %), followed by hemiamblyopia (23.3 %), quadrantanopia (15.3 %) and paracentral scotomata (6.7 %). About 70 % of all VFD patients had a visual field sparing of 5° …or less (macula or foveal sparing). Patients with VFDs frequently showed two types of disabilities: hemianopic alexia was subjectively reported and objectively found in 5090 % of all patients, and visual exploration deficits in the scotoma were complained and found in 1770 % of the VFD patients. While hemianopic alexia was related to parafoveal visual field sparing, and additionally to visual acuity in patients with bilateral VFDs, visual exploration deficits were correlated to the size of the area in the scotoma in which the patient searched for a stimulus with saccadic eye movements (search field). The size of the search field in the intact hemifield was not related to visual exploration deficits in unilateral VFDs. As a third disability, visual-spatial deficits in VFD patients are summarized. In the second part, restorative and compensatory treatment approaches for postchiasmatic VFDs are reviewed. Partial restitution of blind regions in the visual field is achieved in the majority of patients treated with purely restorative methods including saccadic localization or light detection in the scotoma. However, the amount of the visual field recovered is limited to 512° (mean) in 90 % of these patients. Compensatory treatments seek to improve the substitution of the lost field region by large-scale saccadic eye move-ments to the scotoma, spatially organized search strategies in both visual hemifields, and by training small-scale eye movements required for reading. Significant improvements in these areas are achieved in 95 % of all VFD patients with these treatment techniques, with documented transfer to visually related activities of daily living. Furthermore, a significant though limited visual field increase of 57° is achieved in 30 50 % of patients treated in this way. In the final section, promising approaches that might lead to new treatment techniques for VFDs are reviewed. Among these are the gaze-dependant modulation of scotomata, training-dependant enlargement of the useful field of view, a nd t he uncovering of residual visuomotor capacities to visual stimuli in a scotoma. Show more

Keywords: Hemianopia, recovery, reading, visual search, space perception, gaze

Citation: Restorative Neurology and Neuroscience, vol. 15, no. 2-3, pp. 255-271, 1999

Authors: Kasten, Erich | Poggel, Dorothe A. | Müller-Oehring, Eva | Gothe, Janna | Schulte, Tilman | Sabel, Bernard A.

Article Type: Research Article

Abstract: Purpose: Brain damage is often accompanied by visual field defects which have been considered to be non-treatable. In recent years, however, new diagnostice methods have revealed hitherto unknown residual vision, which was found, for instance, in transition zones near the blind visual field sectors and in spared islands of vision within the blind regions ("blindsight"). Furthermore, animal studies revealed a high degree of plasticity in the visual system suggesting the possibility that recovery of vision may …be induced by systematic visual training. Methods: Here we summarize a series of studies with patients suffering from visual field defects after brain lesion using some most recently developed computer-based programs for the diagnosis and treatment of visual field defects. Specifically, high-resolution perimetry (HRP) was applied to first diagnose residual function in or near the "blind" sector of the visual field. Thereafter, visual restitution training (VRT, see Kasten et al., Nature med. 4, 1998, p. 1083) was used daily for 6 months to provide systematic stimulation of these areas of residual vision. Results: In a number of studies, we have observed not only residual visual functions within or near the field defect, but we were also able to follow the course of spontaneous recovery of visual functions within weeks or months after visual system damage. Furthermore, even long after spontancous recovery is complete, computer-based visual restitution training (VRT) in or near the areas of residual vision results in a significant enlargement of intact areas, both after optic nerve damage and postchiasmatic lesions. Using VRT, we found a border shift of about 5 degrees of visual angle which cannot be explained by eye movements or eccentric fixation. We observed a transfer of this training effects to other tasks such as form and color detection, as well as to tests of visual exploration which were not specifically trained. Moreover, 72 % of the patients reported subjective improvements of vision. Training-induced visual field enlargement persisted for at least one year, even in the absence of training beyond 6 months of treatment. Conclusions: The visual system possesses a remarkable plasticity which becomes apparent in visual field enlargement during spontaneous recovery and specifie visual training. Animal studies indicate that a minimum number of residual neurons surviving the lesion, in the order of 10%, provides a sufficient substrate for recovery of vision. Though the precise mechanisms of training-induced visual field enlargement need to be further explored, VRT can be introduced for routine clinical treatment of patients with visual field defects. Show more

Keywords: Plasticity, functional restitution, visual field defects, residual neuronal structures, training, rehabilitation

Citation: Restorative Neurology and Neuroscience, vol. 15, no. 2-3, pp. 273-287, 1999