11/432. Traumatic cataract presenting with unilateral nasal hemianopsia. A 56-year-old man developed a nasal field defect in his left eye 3 months after a traumatic accident. An examination showed a posterior subcapsular cataract in the left eye with no neurologic deficits. Humphrey 24-2 visual field testing revealed a nasal hemianopsia in the left eye. After cataract extraction and intraocular lens implantation, the patient's visual field returned to normal. This case shows that a cataract can present with a localized visual field deficit, which may be corrected by cataract extraction. ( info) |
| The act of attending has frequently been equated with visual awareness. We examined this relationship in 'blindsight'--a condition in which the latter is absent or diminished as a result of damage to the primary visual cortex. Spatially selective visual attention is demonstrated when information that stimuli are likely to appear at a specific location enhances the speed or accuracy of detection of stimuli subsequently presented at that location. In a blindsight subject, we showed that attention can confer an advantage in processing stimuli presented at an attended location, without those stimuli entering consciousness. attention could be directed both by symbolic cues in the subject's spared field of vision or cues presented in his blind field. cues in his blind field were even effective in directing his attention to a second location remote from that at which the cue was presented. These indirect cues were effective whether or not they themselves elicited non-visual awareness. We concluded that the spatial selection of information by an attentional mechanism and its entry into conscious experience cannot be one and the same process. ( info) |
13/432. Bitemporal pseudohemianopia related to the "tilted disk" syndrome: CT, MR, and fundoscopic findings. We describe a case of the "tilted-disk" syndrome in a patient with a bitemporal field depression (a pseudohemianopia). CT and MR imaging showed thinning and prolapse of the nasal sectors of the posterior walls of the globes and flattening of the temporal portion of the globes. ( info) |
14/432. Three-dimensional neglect phenomena following right anterior choroidal artery infarction. Neglect in the horizontal and vertical axes of space has been observed after acute right anterior choroidal artery (AChA) lesions. How spatial processing is affected in the radial axis during the acute period following infarction in this region is unknown. We report the case of a 69-year-old man with acute left hemineglect and deficits in 3-dimensional spatial processing following right AChA infarction. His line bisections in 4 spatial conditions, oriented in the 3 primary axes of space, were compared with 6 control participants. The patient's bisections were different from true center and from control performance in all axes. His bisections were to the right, below, and distal to the arithmetic midpoint. This patient's bisection errors show a 3-dimensional neglect pattern following right AChA infarction, supporting the view that processing of all 3 spatial dimensions may be simultaneously disturbed following unilateral right hemisphere lesions. ( info) |
15/432. Pathological perceptual completion in hemianopia extends to the control of reach-to-grasp movements. The neuropsychological phenomenon of blindsight is observed when patients who are cortically blind exhibit residual visual processing capabilities for stimuli presented within their scotoma to which they are otherwise unaware. Cortically blind patients may also exhibit the phenomenon of pathological visual completion in which, paradoxically, they can become aware of a complete visual stimulus even when a significant portion of that stimulus falls within their blind hemifield. In this study, the ability of a blindsight patient (G.Y.) to use visual information to control reach-to-grasp movements to static objects presented within his blind hemifield was investigated. The results indicate that while G.Y. was insensitive to variations in object size when reaching for objects presented entirely within his blind hemifield, his ability to accurately grasp objects located within his blind field was vastly improved if part of the object to be grasped extended into his seeing hemifield. This finding demonstrates that visual awareness can facilitate the visuomotor processing of object form within G.Y.'s apparently blind field, and suggests that the primary deficit in blindsight may be an impairment of visual consciousness rather than an absolute loss of visual function. ( info) |
16/432. Pure homonymous hemianopia due to anterior choroidal artery territory infarction. The most consistently observed neurological deficits in the anterior choroidal artery (AChA) territory infarction are pure motor or sensorimotor syndromes. Visual field defects and higher cortical dysfunction are occasionally accompanied, but pure homonymous hemianopia without motor and sensory symptom has never been reported yet. We present 2 patients with pure homonymous hemianopia, whose MRI disclosed cerebral infarction in the well-known territory of the AChA. In most patients with ischemic stroke, pure homonymous hemianopia indicates infarction in the posterior circulation, particularly in the posterior cerebral artery territory. However, the present cases provide evidence that it can also be caused by infarction in the anterior circulation, i.e. the AChA. ( info) |
17/432. MRI of cerebral alveolar echinococcosis. Cerebral alveolar echinococcosis is rare. We report a case with multiple intracranial masses which show cauliflower-like contrast enhancement pattern on MRI. The lesions originated from hepatic involvement with invasion of the inferior vena cava. ( info) |
18/432. Retinal red-free light photographs in two congenital conditions: a case of optic hypoplasia and a case of congenital hemianopia. Two patients with congenital anomalies involving the optic pathways are described. The first case presented a unilateral hypoplastic optic nerve as well as an ipsilateral inferior conus and an elevated disc. The second case showed the features of homonymous hemianopia with sparing of the macula and decreased visual acuity on the side of the affected cerebral hemisphere. Red-free photographs were obtained in both cases. The importance of this old-new investigative tool in completing a neuro-ophthalmological study is stressed. ( info) |
19/432. An unusual homonymous visual field defect. A 75-year-old man suddenly became aware of an inferior right homonymous visual field defect. Although static perimetry suggested a lesion of the left lateral geniculate nucleus, kinetic perimetry indicated that the presumed homonymous horizontal sectoranopia noted on static perimetry was actually an incomplete homonymous hemianopia with incomplete sparing of the temporal crescent. The location of the lesion was subsequently confirmed by magnetic resonance imaging. This case shows the value of kinetic perimetry in assessing homonymous visual field defects. ( info) |
20/432. Variability not ability: another basis for performance decrements in neglect. OBJECTIVE: To determine reaction time (RT) and its variability, as a function of horizontal spatial position, in subjects with neglect. Background: In neglect, performance is frequently reported a as mean and a decreased ability to perform the task inferred by comparison to control groups. Few studies have examined how consistency and optimal performance relate to spatial neglect. methods: Ten subjects with brain damage, five with and five without spatial neglect, were assessed on a RT task. Subjects responded by pushing a computer key to the onset of a white square appearing on a black screen. The locations of stimuli were randomly varied along the horizontal meridian. RESULTS: For three of five neglect subjects, optimal RT showed no or little relation to horizontal location. Four of five neglect subjects demonstrated an increased variability in RT that correlated with spatial position and which was not present in our brain damaged subjects without neglect. The relationship was not an artifact of left sided stimuli, in general, being processed differently. For the two neglect subjects with the most trials, a significant correlation between RT variability and spatial position existed for left-sided trials alone. Increased variability was not a consequence of simply looking left proportionately less often, nor could a model of multiple compensatory systems operating in parallel explain the enhanced variability. Neither hemianopsia alone nor brain damage per se could account for the spatial modulation of RT variability. CONCLUSIONS: That neglect subjects perform the RT task normally on some trials, even in their 'neglected field', challenges the notion that neglect must reflect an irreparably damaged cognitive system. Performance decrements in neglect can reflect an inability to consistently detect and respond. Evaluating optimal performance and variability of performance can indicate if a capacity has been lost absolutely or merely degraded such that normal performance cannot be sustained. ( info) |