Transfer effects of training-induced visual field recovery in patients with chronic stroke.

OBJECTIVE: Visual training of light detection in the transition zone between blind and healthy hemianopic visual fields leads to improvement of color and simple pattern recognition. Recently, we demonstrated that visual field enlargement (VFE) also occurs when an area just beyond the transition zone is stimulated. In the current study, we attempted to determine whether this peripheral training also causes improvement in color and shape perception and reading speed. Further, we evaluated which measure of VFE relates best to improvements in performance: the average border shift (ABS) in degrees or the estimated amount of cortical surface gain (ECSG) in millimeters, using the cortical magnification factor (CMF). METHOD: Twelve patients received 40 sessions of 1-hour restorative function training (RFT). Before and after training, we measured visual fields and reading speed. Additionally, color and shape perception in the trained visual field area was measured in 7 patients. RESULTS: VFE was found for 9 of 12 patients. Significant improvements were observed in reading speed for 8 of 12 patients and in color and shape perception for 3 of 7 patients. ECSG correlates significantly with performance; ABS does not. Our data indicate that the threshold ECSG, needed for significant changes in color and shape perception and reading speed, is about 6 mm. CONCLUSIONS: White stimulus training-induced VFE can lead to improved color and shape perception and to increased reading speed in and beyond the pretraining transition zone if ECSG is sufficiently large. The latter depends on the eccentricity of the VFE.

Oculomotor behavior of hemianopic chronic stroke patients in a driving simulator is modulated by vision training.

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Effects of vision restoration training on early visual cortex in patients with cerebral blindness investigated with functional magnetic resonance imaging.

Cerebral blindness is a loss of vision as a result of postchiasmatic damage to the visual pathways. Parts of the lost visual field can be restored through training. However, the neuronal mechanisms through which training effects occur are still unclear. We therefore assessed training-induced changes in brain function in eight patients with cerebral blindness. Visual fields were measured with perimetry and retinotopic maps were acquired with functional magnetic resonance imaging (fMRI) before and after vision restoration training. We assessed differences in hemodynamic responses between sessions that represented changes in amplitudes of neural responses and changes in receptive field locations and sizes. Perimetry results showed highly varied visual field recovery with shifts of the central visual field border ranging between 1 and 7°. fMRI results showed that, although retinotopic maps were mostly stable over sessions, there was a small shift of receptive field locations toward a higher eccentricity after training in addition to increases in receptive field sizes. In patients with bilateral brain activation, these effects were stronger in the affected than in the intact hemisphere. Changes in receptive field size and location could account for limited visual field recovery (± 1°), although it could not account for the large increases in visual field size that were observed in some patients. Furthermore, the retinotopic maps strongly matched perimetry measurements before training. These results are taken to indicate that local visual field enlargements are caused by receptive field changes in early visual cortex, whereas large-scale improvement cannot be explained by this mechanism.

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.

Visual field enlargement by neuropsychological training of a hemianopsia patient.

A 58-year old hemianopsia patient was submitted to a two-fold neuropsychological training in order to enhance visual functions in the affected part of his visual field. At first, the visual field was measured perimetrically, to serve as a starting measurement with which after-measurements could be compared. Then, the first training was started: the border area between the intact and the defect visual field was being stimulated by small light spots. The training consisted of repetitive detection threshold measurements. After 27 one-hour sessions, the visual field was being measured again. The visual field appeared to have been enlarged 5 to 12 degrees in the direction of the affected hemifield and contrast-sensitivity thresholds to have been decreased almost at every point in the stimulus-array. Then, a second training started; an eye-movement training. Again, the border area, now shifted outwards, was stimulated. This time, the stimulus concerned a short presentation of light (< 200 msec.) after which the subject, to the best of his abilities had to make an eye-movement to the perceived stimulus-site. Also, he had to categorize the quality of his perception as well as the direction in which the stimulus was thought to be perceived. After 30 sessions, the visual field appeared to have 'grown' just a little bit more, but this seems not to be a significant enlargement. More important, the number of detected stimuli in the supposed 'blind' area had increased, as had the accuracy of the localization of the stimuli. Preliminary results of the detection training of a second subject, also 58 years of age, are presented. Finally, planned actions are discussed.

'When is VISION asked too much'?

The last two decades a shift took place from substitutional/compensatory training to utilisation of residual vision regarding rehabilitation of the visually impaired. Some of the visually impaired are able to use their visual perception nearly as complete as normal seeing people in spite of a severe visual disability. On the other hand, people with nearly normal functions can be severely visually handicapped. To illustrate this, two cases are presented. The first case is a man, aged 47 years, with a juvenile macular degeneration on both eyes. In spite of a very low visual acuity of less then 0.05, he finished an university education and he is able to maintain himself very well in a leading position in a scientific environment, by using adequate low vision devices. Also for his leisure activities, as photography and speed skating, he relies upon visual perception. The second case is a woman, aged 30 years, with nearly normal visual functions, who is not able to read for longer periods caused by conflicting information from the body- and eye movements, and the visual input. This causes sickness during reading. She is unable to use books for her study and is working with recordings on tape. The results of a comprehensive visual assessment will be related to the specific low vision devices and its use.

Towards a classification of visual impairment.

For the rehabilitation of people with impaired vision, it is essential to have adequate (preferably quantitative) information about their residual visual functions. Special attention is given to the extra information provided by the results of measurement of the contrast sensitivity, especially in combination with the results of other measurements, such as the visual field, the amount of intraocular straylight and the visual acuity. The value of the contrast sensitivity function as a predictor of the extent of dysfunctioning in the visual activities of everyday life, such as outdoor vision, reading and recognition of faces, will be discussed. As far as this is concerned, a comparison is made between the value of visual acuity and contrast sensitivity as measures of the extent of vision and visual dysfunctioning.

Spatial contrast sensitivity in unilateral cerebral ischaemic lesions involving the posterior visual pathway.

Contrast sensitivity function was studied in 16 patients with unilateral ischaemic lesions involving the posterior visual pathway. Sixty-two percent of the patients showed contrast sensitivity loss in at least one eye for horizontal or vertical stimulus orientation. Visual perception was distorted in a qualitatively different way according to the anteroposterior site of the lesion. Patients with occipital or occipitotemporal lesions showed high spatial frequency selective losses and patients with temporal or parietal lesions low frequency selective losses. Stimulus orientation selectivity was observed in patients with lesions of the primary visual cortex as well as in patients with lesions anterior to the striate cortex. Contrast sensitivity orientation-selective losses were demonstrated in 14 of the 17 'affected' eyes.

Visual contrast sensitivity in drug-induced Parkinsonism.

The influence of stimulus orientation on contrast sensitivity function was studied in 10 patients with drug-induced Parkinsonism. Nine of the 10 patients had at least one eye with contrast sensitivity deficit for vertical and/or horizontal stimuli. Only generalised contrast sensitivity loss, observed in two eyes, was stimulus orientation independent. All spatial frequency-selective contrast deficits in 15 eyes were orientation dependent. The striking similarity between the pattern of contrast sensitivity loss in drug-induced Parkinsonism and that in idiopathic Parkinson's disease, suggests that generalised dopaminergic deficiency, from whatever cause, affects visual function in an analogous way.

Spatial contrast sensitivity in benign intracranial hypertension.

Spatial Contrast Sensitivity (CS) was studied in 20 patients with benign intracranial hypertension (BIH). At presentation CS loss was found in 43% of the eyes, and impairment of visual acuity attributed to BIH in only 16%. Nine patients had blurred vision or visual obscurations, all of whom had abnormal CS. The clinical application of CS measurement in BIH for monitoring the progression or regression of the disease is illustrated by serial measurements in 11 patients. Progressive visual loss in longstanding papilloedema and improvement of visual function in subsiding papilloedema can occur without any change in Snellen acuity or visual field charting.

Effect of stimulus orientation on contrast sensitivity in Parkinson's disease.

We studied the effect of stimulus orientation on contrast sensitivity function in 21 patients with Parkinson's disease and in 10 normal subjects. This was done by measuring contrast sensitivity over a range of spatial frequencies for vertical and horizontal sine wave grating stimuli. There was a great test-retest consistency in normal subjects and patients. Fifteen of the 21 patients showed contrast sensitivity deficit in at least one eye. Orientation-specific loss was demonstrated in 17 of the 25 "affected" eyes. The most frequent type of orientation-specific loss was a notch defect, which preferentially affected the middle spatial frequencies. We attribute orientation-specific and spatial frequency-selective loss in Parkinson's disease to a functional disruption of neurons on the visual cortex.

Contrast sensitivity for oscillating sine wave gratings during ocular fixation and pursuit.

The influence of pursuit eye movements on the visibility of sine wave gratings was investigated by the simultaneous measurement of eye movements and contrast thresholds under different viewing conditions. It was concluded that: 1. with moving gratings contrast sensitivity during ocular pursuit was equal to contrast sensitivity during maintained fixation on a stationary target, provided that the magnitude of retinal image motion (0-20 deg/sec) was equal in both cases; 2. accurate pursuit eye movements led to a paradoxical suppression of the visibility of low spatial frequency gratings; 3. the visibility of high spatial frequency gratings remained unchanged during accurate pursuit eye movements; 4. iso-contrast-sensitivity resulting from both pursuit and non-pursuit conditions could be used to quantify the ocular pursuit performance.

Spatial contrast sensitivity in clinical neurology.

We studied contrast sensitivity function in normal subjects and in three illustrative cases with various neurological disorders. This was done by measuring contrast sensitivity over a range of spatial frequencies for vertical sinewave grating stimuli. It is demonstrated that contrast sensitivity function can give information about visual function not obtainable by conventional test procedures.

Effect of levodopa treatment on contrast sensitivity in Parkinson's disease.

We studied contrast sensitivity function in 10 parkinsonian patients before and after levodopa treatment. Pretreatment contrast sensitivity function was abnormal in 16 of the 20 eyes. After treatment, only high-frequency loss was observed in 6 eyes. All other types of deficit disappeared under treatment. These changes of contrast sensitivity function following treatment suggest that dopamine is a functional transmitter in the visual pathways.

Spatial contrast sensitivity and the diagnosis of amblyopia.

The relationship was studied between spatial contrast sensitivity function and type of pathology of the visual system. Two characteristics were found to be typical for amblyopia: there is a discrepancy between the high-frequency cut-off ('grating acuity') and the Snellen acuity; the contrast sensitivity is strongly dependent on the width of the stimulus. In optic nerve degeneration a decrease in contrast sensitivity is found at low spatial frequencies. Decreased contrast sensitivity at high spatial frequencies is atypical but occurs in those disorders associated with decreased Snellen visual acuity. From these findings a relationship is defined which enables spatial contrast sensitivity tests to be used to differentiate between amblyopia and optic nerve degeneration.

Contrast sensitivity in Parkinson's disease.

We studied contrast-sensitivity function in 39 patients with Parkinson's disease. Sixty-four percent of the patients showed contrast-sensitivity loss in one or both eyes. The abnormality was not related to the first symptom or the severity of disease. Sensitivity loss at intermediate frequencies (notch loss) in 30% of the "affected" eyes suggested a cortical component. These findings support the belief that there is a widespread neurotransmitter deficiency in Parkinson's disease.

Minimum procedures for visual electrodiagnostic testing.

A set of procedures for the electroretinogram, electrooculogram, and pattern and luminance visual evoked cortical potentials was defined by representatives from all Dutch University Eye Clinics in order to promote standardization of procedures for routine diagnostic testing. The procedures have been selected to obtain an answer to most electrodiagnostic questions of frequent occurrence with a minimum of equipment and examination time. An individual examiner may add other procedures to the proposed program to extend and diagnostic possibilities.

Foveal inhibition measured with suprathreshold stimuli.

Foveal inhibition has been studied with elementary stimuli presented at increment threshold luminance and with suprathreshold stimuli. Both kinds of stimuli yield a similar kind of propagating inhibition. The results of this study are compared with previously published data on peripheral inhibition. The inhibition produced with spatially extended stimuli is described in terms of the ideas derived from measurements on elementary stimuli. This model is tested for a metacontrast stimulus consisting of a disk which is followed after a certain delay by a ring surrounding the disk.

The influence of the background on the generation of inhibition.

The conditions leading to the generation of propagating inhibition have been investigated. The use of elementary point flashes as probes makes it possible to detect both the site and the time of inhibition with a high precision. The background luminance is found to influence the extent of inhibition. When no background illumination is present, no inhibition is detected. When only part of the background is illuminated, inhibition is sometimes found, and sometimes not. Experiments involving systematic buildup and breakdown of a background luminance field showed that inhibition only occurs when luminance is present within the range within which the inhibition effects operate (about 25 min of arc).

Contrast detection and its dependence on the presence of edges and lines in the stimulus field.

The influence of sharp luminance discontinuities (dark lines and edges) in the stimulus field on the contrast sensitivity has been measured using sinusoidal gratings. Merely by changing the position of edges or lines in the stimulus field, it is possible to alter the contrast sensitivity by a factor of 3 or more. The distance from which such a discontinuity can affect the contrast sensitivity depends on the spatial frequency of the grating itself, and can be up to several degrees for gratings of low spatial frequency. No difference could be found between the effect of edges and the effect of very thin (5 min of arc) dark lines on the contrast sensitivity. The apparently conflicting experimental results in the literature concerning the relationship between the number of periods in a grafting and the contrast sensitivity, and especially concerning the influence that the surround of the grating has on this relationship, can be ascribed to the effect of these luminance discontinuities. In all cases where the number of periods was reported to have a large effect on the contrast sensitivity (up to a factor 10), the position of edges or lines in the stimulus field was also varied when the number of periods was changed. The change in the contrast sensitivity is no more than a factor 2 to 3 when there are no lines or edges in the grating surround.