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Restitution of Visual Function in Patients with Cerebral Blindness

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Restitution of Visual Function in Patients with Cerebral Blindness J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp.42.4.312 on 1 April 1979. Downloaded from Journal ofNeurology, Neurosurgery, andPsychiatry, 1979, 42, 312-322 Restitution of visual function in patients with cerebral blindness J. ZIHL AND D. VON CRAMON From the Max-Planck-Institut fur Psychiatrie, Miinchen, Germany SUMMARY 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. Although only contrast sensitivity was trained, the observed improvement was not limited to this visual function. Visual acuity, critical flicker fusion, and colour perception also showed an improve- ment 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 a Protected by copyright. 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. Lesions within the central visual pathways do not may be abrupt or gradual (Korner and Teuber, necessarily result in absolute and permanent visual 1973). Visual fields with sharp scotoma boundaries field defects (Teuber, 1975). Perimetric "blind" or show only a slight recovery of function, whereas impaired visual field areas may fluctuate in sensi- for visual fields with rather gradual borders of the tivity (Bender and Teuber, 1946). Recovery of defect some degree of recovery can be observed visual function has been observed in patients with (Teuber, 1974; Zihl et al., 1977b). postchiasmatic lesions although return of vision is The question arises whether the level of rarely complete (Bergmann, 1957; Symonds and neuronal sensitivity can be modulated by system- Mackenzie, 1957). Reappearance takes place in a atic external stimulation in order to improve re- definite temporal order: sensation of light and covery of visual function. An increase in sensitivity http://jnnp.bmj.com/ motion, form perception, colour perception in impaired or perimetrically "blind" parts of the (Poppelreuter, 1917; Riddoch, 1917). visual field may result in the restitution of vision Bender and Teuber (1946) suggested that fluctua- in these areas and thus in an enlargement of the tions in the extent and size of a cortical scotoma visual field. Evidence for such an increase in sen- are correlated with the variation of neuronal sitivity in impaired or scotomatous visual field sensitivity in the cortical area which is affected by parts has come from experiments with monkeys the lesion. In the corresponding visual field parts- (Cowey and Weiskrantz, 1963; Cowey, 1967). that is, at the border of the visual field-fluctua- Visual stimulation in the area between intact and on September 29, 2021 by guest. tion and extinction of visual function can be blind parts of the visual field leads to a decrease of observed. For these parts of the visual field a the scotoma. Observations in human subjects are diurnal variation of light sensitivity was found in agreement with the effect of stimulation in (Zihl et al., 1977a). The transition between the monkeys. Stimulation of impaired visual field areas intact parts of the visual field and the scotoma with cortically reduced visual functions increases sensitivity and visual field size, although fatigue Address for correspondence and reprint requests: J. Zihl, Max- Planck-Institut fur Psychiatrie, Kraepelinstrasse 10, 8000 Munchen 40 may take place rapidly and result in an overall Federal Republic of Germany. reduction of visual function (P6ppel et al., 1978). Accepted 6 October 1978 The purpose of this paper is to present evidence 312 J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp.42.4.312 on 1 April 1979. Downloaded from Restitution of visual function in patients with cerebral blindness 313 that diminished visual function can be improved had a diameter of 116 min visual angle; target by systematic stimulation of the impaired areas of luminance was 32 cd/M2. The patient pushed a the visual field. Since light sensation reappears button when he could detect flickering of the first in blind areas, this visual function was trained target (for ascending series) or when flicker was no in order to improve visual performance. To demon- longer detectable (for descending series). For test- strate the central nature of the increase in con- ing visual acuity, the patient's task was to trast sensitivity obtained by the training procedure, indicate whether he saw a circular or a diamond- interocular transfer was tested. We also investi- shaped target. Luminance of the targets was gated whether improvement takes place only in a 32 cd/M2 and they were presented for one second. defined area of the visual field (according to the Order of presentation was randomised. Errorless central representation of the retina). In addition, performance was chosen as the criterion of acuity. periods without training were included to show Critical flicker frequency and visual acuity were that the increase in sensitivity depends on the determined with the Tubinger perimeter. For test- training session and is not the result of spon- ing binocular colour perception, the Farnsworth- taneous recovery. Munsell 100-hue test was used (Farnsworth, 1943). Methods TRAINING PROCEDURE Visual training was performed with the Tubinger VISUAL FIELD EXAMINATION perimeter. The method of limits was used to im- The visual fields were tested by dynamic and static prove sensitivity to light stimuli. Monocular and perimetry using the Tubinger perimeter (Sloan, binocular contrast thresholds were determined 1971; Aulhorn and Harms, 1972). The patients several times at a constant eccentricity in the fixated a red spot of light (10 or 30 min visual area between visual field and scotoma. The inter- angle in diameter) at a distance of 330 mm. Back- stimulus interval between presentations was about Protected by copyright. ground luminance was 3.2 cd/M2. Head position three seconds; time between measurements was in was held stable by a chin rest; eye position was the range of 10-30 seconds in order to prevent controlled through a telescope. fatigue (Singer et al., 1977). As a control of the For dynamic perimetry, the target (diameter patient's detection strategy, blanks were inter- 116 min visual angle; luminance 32 cd/M2) was spersed among targets. Usually, 15-20 contrast moved with a constant velocity of about 20/s from thresholds were determined in one session with a the periphery towards the centre of the visual field. break of about five minutes after five measure- The patient had to push a button whenever he ments. detected the target. The border of the visual field The patient was instructed to fixate a red spot was determined for 16 meridians, and the sequence of light in the centre of the homogeneously illumi- of measurements along the different meridians was nated sphere (background luminance 3.2 cd/M2), randomised. The visual fields were tested under and to direct his attention to the area where train- monocular and binocular conditions. ing was performed. Within training sessions, the Static perimetry was performed by measuring patients were reinforced for their fixation and binocular increment threshold using the method of their attention. They were not informed about an http://jnnp.bmj.com/ limits. Fixation point and background luminance increase or decrease in sensitivity until they experi- were the same as for dynamic perimetry. Target enced a progress in vision in their everyday life diameter was 69 min visual angle; presentation outside the laboratory. Training sessions were per- time 500 ms. Target luminance was chosen well formed daily at the same time for each patient; above or below threshold level and was then de- usually one session took an hour. creased or increased in steps of 0.1 log units. When the patient detected three targets consecutively, CONTROL OF TRAINING EFFECTS the luminance of the first of these was defined as Visual fields were mapped before and after training on September 29, 2021 by guest. the threshold for the ascending method. For the sessions using dynamic perimetry. In addition light- descending series of threshold measurements, the difference threshold was measured along the luminance of the last seen target was defined as meridian selected for training before and after the threshold-that is, when after this target was training; the difference was taken as change in seen, three consecutive targets were not detected sensitivity. For determination of the retinotopic by the patient. dependence of improvement, increment threshold In addition critical flicker frequency (CFF), was determined at various points surrounding the visual acuity, and colour perception were tested position of training. To test interocular transfer, for both eyes. For measurement of CFF the target training was performed monocularly. Transfer
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