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Show Tournai of Clmical Neuro- ophthalmololiY 11( 1 J: 62- 65, 1991. Reappearance of the Visual Percept After Intentional Blinking in a Patient with Balint's Syndrome D. Gottlieb, M. D., R. Calvanio, Ph. D., and D. N. Levine, M. D. © 1991 Raven Press, Ltd., New York We present a patient with Balint's syndrome who complained of fading of the scenes under visual fixation. When he intentionally blinked, the faded visual percept reappeared. The disappearance of the visual percept may be explained as the result of either unstable visual fixation or of saturation of the visual pathways. The role of blinking in reviving the visual percept may be explained accordingly as causing a refixation of the target under visual fixation or as resetting the visual pathways for visual processing. Key Words: Balint's Syndrome- Fading- Blink. From the Neurology Services, Spaulding Rehabilitation Hospital and Massachusetts General Hospital, and the Department of Neurology, Harvard Medical School, Boston, Massachusetts, U. S. A. . Address correspondence and reprint requests to: Dr. D. Gottlieb at Spaulding Rehabilitation Hospital, 125 Nashua Street, Boston, MA 02114, U. S. A. 62 The major clinical characteristics of Balint's syndrome include disorders of visually triggered eye movements, decreased blink to visual threat, impaired eye- hand coordination, and disturbances of visuospatial attention ( 1- 3). Another clinical characteristic is fading of visually fixated targets ( 1,49). We describe a patient with right parietal and left occipital infarcts presenting as Balint's syndrome. When he looked at a visual object, it faded after several seconds, but it would reappear after he intentionally blinked. Such a reclarification of the visual percept by blinking has not, to the best of our knowledge, been previously discussed. CASE REPORT An 80- year- old right- handed retired male accountant had no history of neurological disease until he underwent coronary artery bypass grafting. Postoperatively he was confused. Cranial computerized tomography scan showed generalized atrophy, right parietal and left occipital infarcts, and an old lacunar capsular infarct. Confusion cleared gradually during the week, but visual problems persisted and left- sided weakness was noted. Initially he could not distinguish light from dark and felt that he had a " white screen" in front of him. Several days later he could distinguish forms, but in a fragmented mode, and he could not recognize faces. He was transferred to a rehabilitation hospital after 17 days. On initial examination he was awake and alert. He complained of blurred vision and that the objects he observed disappeared or faded away. He was well oriented to the circumstances of his hospitalization and understood that he had had a stroke. General attention, language, memory, and reasoning were preserved, but visual perception was impaired. Mostly he had difficulty in " making / VISUAL PERCEPT AND BALINT'S SYNDROME 63 sense" of what he saw. When shown a thematic picture, he could identify its different components but only partially succeeded in comprehending it by using a process of inference. When shown a table with different objects, he saw the whole group. But when he had to name each object separately, he could not do so in an organized way, repeatedly identifying the same items. When asked to trace a simple design, he failed because he could focus his attention on the tip of the pencil or the line to be traced, but not on both simultaneously. Scenes he observed would initially appear clear and after a few seconds they would either fade away gradually or ' jiggle' out of focus and disappear. This would happen after 10-- 20 seconds of attentive observation of a target. He could then make it reappear in its initial clarity for J- 7 seconds, by intentionally blinking his eyes. This sequence could be repeated 2- 3 times. Examination of the cranial nerves revealed reactive pupils and full confrontational visual fields. Visual acuity was impossible to test formally but it was estimated to be in the normal range, as judged by his picture identification. Shifting of gaze and smooth pursuit to visual targets in the peripheral visual fields was slow and irregular when he started from the primary position of gaze, and was more so to the left. Return of gaze to the center and shift towards an auditory stimulus were smooth and quick. Motor tests showed only a mild left hemiparesis. Nevertheless, he could not reach effectively for objects in space. Misreaching was most pronounced with the left hand into the left visual field. This visuomotor disturbance prevented him from feeding himself, but once the spoon was put in his hand he could bring it to his mouth without effort. More detailed studies revealed the following: Although he could not formally perform a line cancellation test ( lO) because he would misreach for all of the targets, it was evident from his performance that his spatial attention was deviated to the right. Similar tendencies were noted in his attempts to draw figures. Tachistoscopic hemifield presentation confirmed a significant delay in recognizing a stimulus in the left visual field compared with the right. Spatial orientation tested with the Benton Line Orientation Test ( 11) was correct except for matching the horizontal line with a 45- degree tilt. In a luminous rod orientation test ( 12) in a dark room, he again misjudged the horizontal alignment by + 20 degrees. Introduction of a tilted frame did not change the results. His own drawings of horizontal and vertical lines were accurate. Depth perception from a lO- foot distance was cor-rect, but at 20 feet he perceived 2 fingers lO inches apart as equidistant. Inability to decompose or to integrate his visual attention showed in many tasks. A 6- pointed star was perceived as such but not as the two colored triangles of which it was composed. Despite correct object recognition, he failed to identify complex devices; thus he saw a seesaw as a ' group of tubes'. Single color identification was intact but two colors side by side caused one of them to become blurred. Despite an excellent sense of humor, he could not grasp the joke in any of ten cartoons, although their details were well described. He could not identify single letters of the alphabet, and the ability to identify them did not improve when luminous letters were presented in a dark room ( thus a ' T would be ' a vertical rod and another one above it'). The difficulties in visual perception were evident in distant vision too; he could not read the clock on the wall, and the view from his window was fragmented and incomprehensible ( for example, he saw the cars driving on a bridge but did not see the bridge). In contrast to visual perception, visual imagery and memory were relatively preserved. Seven out of ten objects were recalled immediately after recognition; topographic directions were visualized correctly, and complex devices were described accurately. Intact language and memory functions were reflected in a normal WAIS- R verbal I. Q. of 114 ( eighty- second percentile) with a subtest range from a low of 105 ( arithmetic) to a high of 120 ( digit span). His impaired visual perception was reflected in a WAIS- R Performance I. Q. of 65 ( fourth percentile) with a similar subtest range from a low of 55 ( digit symbol) to a high of 75 ( block design). The fading away of a visual target was most evident when he fixated a single small object ( e. g., a black dot); the object would fade away under his unshifted gaze. This experience was frustrating since the more he concentrated, the quicker the target would blur and fade away. His spontaneous rate of blinking was normal- 20/ minute. But when he observed an object attentively, the rate would decrease to 4- 6/ minute. During the subsequent 30 days of his recovery he was able to engage in increasingly demanding tasks. On examination, eye movements were improved. Misreaching still occurred when he reached for targets in the peripheral visual fields, but it was of no functional significance. Simultanagnosia could still be demonstrated but only in higher- level tasks such as reading. Thus he could now read both real and pseudowords well, but he could not decompose them and read letter by letter. The phenomenon of I Clin Neuro- ophthalmol, Vol. 11. No.!. 1991 64 D. GOTTLIEB ET AL. the fading away of the visually attended object persisted, but he complained of it less. However it could readily be elicited by asking him to fixate a target, at which time his rate of spontaneous blinking would decrease. An intentional blink would cause the blurred image to reappear clearly until it faded again. DISCUSSION Disappearance of the visual percept has been reported in Balint's syndrome ( 1,4-- 9). Two different mechanisms may be proposed to explain it. Ullstable Visual Fixation Although the eyes may appear still to clinical observation, the process of visual fixation involves two types of eye movements-- microsaccades and slow drift. Microsaccades are used to explore the fixated object on a miniature scale. Both microsaccades and slow drift can be used to recenter a visual stimulus on the fovea. Macrosaccades to eccentric visual targets and ordinary smooth pursuit of moving visual objects were disturbed in our patient and in other patients with Balint's syndrome ( 1- 3). Since microsaccades and slow drift appear to be small- scale versions of ordinary saccades and pursuit movements ( 13), they could be impaired in a similar way. In fact, miniature eye movement recordings in patients with bilateral posterior cerebral damage have demonstrated increased amplitude of slow drift and microsaccades ( 14). It is therefore possible that the visual percept is lost because of poorly maintained fixation and because the disorganized eye movements are unable to redirect the fovea back to the target, once it has been lost ( 7). Saturation of the Visual Pathways Loss of an image fixated on the retina may occur in normal individuals ( 15- 19). It has been observed when the stimulus pattern has been constrained to move with the eye so that no motion of the stimulus relative to the retinal array is permitted ( 15,16). Lowering the salience of the stimulus from its background ( e. g., equiluminance) also causes fading, without the need to stabilize the image on the retina artificially ( 17). Such fading has been explained as being the result of adaptation of the visual sensory system. In the normal individual, adaptation during attentive visual fixation does not occur because the eyes are constantly moving, even though they appear to be still. The miniature , ,'"~ I 71. No 1,1991 eye movements ( microsaccades, slow drift, and tremor) create constant motion of the image over the array of retinal receptors and prevent adaptation. In pathological conditions, temporal adaptation of the visual system occurs more rapidly ( 20,21), and this abnormally rapid adaptation has been proposed to be a cause for the disappearance of the visual percept. In our patient the miniature eye movements during visual fixation were not efficient enough to overcome the abnormally rapid visuosensory adaptation, so that fading of the percept occurred. Thus, the fading away of the visual percept could be explained as a pathological intensification of the physiological process mediating visual sensory adaptation. The clinical characteristics of our patient do not favor either of these two mechanisms. The disappearance of the visual percept during visual fixation was described in different terms. At times the object in front of him would " jiggle:' and at other times it would " fade away" or " gradually disintegrate." Sometimes it would simply " get blurred." Judging by his subjective comments, both mechanisms for disappearance of the visual percept were in action. Observing him while he complained that the object faded away made it clear that this could happen while ' no gross deviations of the eyes from fixation occurred. This observation is reinforced by electro- oculographic studies of patients with simultanagnosia ( 22). These demonstrated correct fixation of the target while the visual percept faded. However, neither the clinical observation nor conventional electrooculography are sensitive enough to record the miniature eye movements ( 23). Abnormalities in the behavior of these miniature eye movements were probably responsible for our patient's reports that stationary visual objects moved or jiggled. The question of whether these represent a primary phenomenon or an epiphenomenon demands further recordings of the miniature eye movements in patients with Balint's syndrome. Finally, the behavior of our patient was characterized by the reappearance of the faded visual percept with voluntary blinking. The revival of the same percept indicated that the target was either back, or still under, visual fixation. Two possible mechanisms may be suggested. First, closure of the eyelids changes the pattern of stimulation so that reopening the lids allows the stimulus to encounter a visuosensory system that is no longer adapted ( 24,25). In this regard it has been suggested that in the normal individual, blinking resets visual sensory transmission, removing inhibitory postsynaptic potentials in thalamic neurons VISUAL PERCEPT AND BALINT'S SYNDROME 65 that are associated with adaptation ( 9). Second, the blink may facilitate and be coordinated with a miniature saccade. Facilitation of saccades by blinking has been reported by several investigators ( 26- 28). Such a blink- induced microsaccade would be beneficial both in refixating the target and in erasing adaptation by elevating the visual threshold ( 29) and by presenting a new pattern of stimulation on the array of receptors. In a previous report ( 9), it was suggested that visual fading in a patient with Balint's syndrome may have been caused by a decrease in the patient's rate of spontaneous blinking. In our patient, visual fading occurred at a blink rate which, although reduced from his baseline, was within the normal range observed in attentive tasks ( 30). Also, it is noteworthy that the reduction in spontaneous blink rate reported in patients with Parkinson's disease and progressive supranuclear palsy ( 25,31) has not been associated with visual fading. Therefore, it seems to us that reduction in blink rate alone is not sufficient to cause disappearance of a visual percept. 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