Cases reported "Blindness, Cortical"

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1/10. visual perception of motion, luminance and colour in a human hemianope.

    Human patients rendered cortically blind by lesions to V1 can nevertheless discriminate between visual stimuli presented to their blind fields. Experimental evidence suggests that two response modes are involved. patients are either unaware or aware of the visual stimuli, which they are able to discriminate. However, under both conditions patients insist that they do not see. We investigate the fundamental difference between percepts derived for the normal and affected hemifield in a human hemianope with visual stimuli of which he was aware. The psychophysical experiments we employed required the patient, GY, to make comparisons between stimuli presented in his affected and normal hemifields. The subject discriminated between, and was allowed to match, the stimuli. Our study reveals that the stimulus parameters of colour and motion can be discriminated and matched between the normal and blind hemifields, whereas brightness cannot. We provide evidence for associations between the percepts of colour and motion, but a dissociation between the percepts of brightness, derived from the normal and hemianopic fields. Our results are consistent with the proposal that the perception of different stimulus attributes is expressed in activity of functionally segregated visual areas of the brain. We also believe our results explain the patient's insistence that he does not see stimuli, but can discriminate between them with awareness.
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2/10. Neuronal representation of object orientation.

    The dissociation between object identity and object orientation observed in six patients with brain damage, has been taken as evidence for a view-invariant model of object recognition. However, there was also some indication that these patients were not generally agnosic for object orientation but were able to gain access to at least some information about objects' canonical upright. We studied a new case (KB) with spared knowledge of object identity and impaired perception of object orientation using a forced choice paradigm to contrast directly the patient's ability to perceive objects' canonical upright vs non-upright orientations. We presented 2D-pictures of objects with unambiguous canonical upright orientations in four different orientations (0 degrees, -90 degrees, 90 degrees, 180 degrees ). KB showed no impairment in identifying letters, objects, animals, or faces irrespective of their given orientation. Also, her knowledge of upright orientation of stimuli was perfectly preserved. In sharp contrast, KB was not able to judge the orientation when the stimuli were presented in a non-upright orientation. The findings give further support for a distributed view-based representation of objects in which neurons become tuned to the features present in certain views of an object. Since we see more upright than inverted animals and familiar objects, the statistics of these images leads to a larger number of neurons tuned for objects in an upright orientation. We suppose that probably for this reason KB's knowledge of upright orientation was found to be more robust against neuronal damage than knowledge of other orientations.
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3/10. hemolysis, elevated liver enzymes, and low platelet count (HELLP) syndrome with acute cortical blindness.

    The coincidence of hemolysis, elevated liver enzymes, and low platelet count (HELLP) syndrome and cortical blindness is an uncommon but very dramatic event. We describe a case of hellp syndrome complicating with acute cortical blindness before delivery. A 27 year-old woman, gravida 1, para 0, with normal medical history, was referred to our emergency department at the 33th week of gestation due to headache, vomiting, and blurred vision. The ophthalmologic examination showed intact pupillary light reflexes and normal ophthalmoscopic findings, but no light perception in either eye. brain computed tomography showed normal findings. hellp syndrome and preeclampsia was diagnosed based on the findings of hypertension and proteinuria as well as laboratory data. Prompt delivery was performed in order to achieve good maternal and neonatal outcomes.
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keywords = perception
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4/10. Direction-specific motion blindness induced by focal stimulation of human extrastriate cortex.

    Motion blindness (MB) or akinetopsia is the selective disturbance of visual motion perception while other features of the visual scene such as colour and shape are normally perceived. Chronic and transient forms of MB are characterized by a global deficit of direction discrimination (pandirectional), which is generally assumed to result from damage to, or interference with, the motion complex MT /V5. However, the most characteristic feature of primate MT-neurons is not their motion specificity, but their preference for one direction of motion (direction specificity). Here, we report that focal electrical stimulation in the human posterior temporal lobe selectively impaired the perception of motion in one direction while the perception of motion in other directions was completely normal (unidirectional MB). In addition, the direction of MB was found to depend on the brain area stimulated. It is argued that direction specificity for visual motion is not only represented at the single neuron level, but also in much larger cortical units.
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keywords = perception
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5/10. Reversible cortical blindness in preeclampsia.

    PURPOSE: To report the clinical course and magnetic resonance imaging (MRI) findings in a 28-year-old woman with preeclampsia and reversible cortical blindness. DESIGN: Interventional case report. methods: The patient presented at the 37th week of pregnancy with headache and hypertension. The next day, her visual acuity decreased to light perception in both eyes. After emergent cesarean section, examination revealed reactive pupils and normal fundi. RESULTS: magnetic resonance imaging of the brain showed areas of increased signal in both occipital lobes. One month later, at which time the patient's visual acuity had returned to 20/20, follow-up MRI showed complete resolution of radiologic abnormalities. CONCLUSIONS: Cortical blindness is a rare complication of preeclampsia. In this case, cortical blindness was reversible and most likely due to vasogenic edema rather than vasospasm.
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keywords = perception
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6/10. Functional magnetic resonance imaging mirrors recovery of visual perception after repetitive tachistoscopic stimulation in patients with partial cortical blindness.

    We investigated three patients with partial cortical blindness after brain injury by means of functional magnetic resonance imaging (fMRI) before and after the application of a daily visual stimulation-therapy over a period of 6 months. Before therapy, fMRI data showed a severely reduced blood-oxygen-level-dependent (BOLD) signal in primary visual cortex when compared to healthy volunteers. Following several months of rehabilitative therapy a neuropsychological improvement of visual functions was accompanied by an increase in BOLD signal of residual perilesional regions whereas fMRI data of the control group remained unchanged. A high capacity of functional recovery and synaptic plasticity of surviving perilesional neuronal structures of primary visual cortex followed by an increased input into post-connected visual areas can be discussed as a basis for the reoccurrence of visual functions.
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keywords = perception
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7/10. Partial recovery from cortical blindness following carbon monoxide intoxication.

    patients with carbon monoxide (CO) intoxication may show neurological signs such as headache, seizures, extrapyramidal findings, and coma. However, cortical blindness is rare in these cases. This study describes a woman exhibiting confusion and axial rigidity after CO intoxication. Ten days after intoxication, her pupils were isonormocoric and reactive to light. A fundoscopic examination was normal, but visual acuity was light-perception in both eyes. There were diffuse EEG slow waves. magnetic resonance imaging (MRI) demonstrated bilateral hyperintensity in the basal ganglia. The P100 latencies of visual evoked potentials (VEP) were increased and dispersed. One year later, the patient's visual acuity was almost normal and VEPs showed mild dispersion in P100 latencies. The authors found this case of interest because cortical blindness due to CO intoxication is only rarely seen with a relatively good outcome.
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ranking = 0.2
keywords = perception
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8/10. Blindsight in children: does it exist and can it be used to help the child? Observations on a case series.

    Damage to the occipital lobe of the brain results in hemianopia when unilateral, and cerebral blindness when bilateral. However, in some cases a degree of visual function persists in the blind visual field. This aim of this study was to describe this phenomenon of 'blindsight' in a cohort of children with brain-damage and to relate the clinical features to their visual evoked potentials. We performed a retrospective analysis of 541 case records of children referred to a tertiary vision-assessment clinic in the Royal Hospital for Sick Children, Glasgow, UK from 1992 to 2002. A total of 541 patients were analyzed (243 females, 298 males; age range 2 mo to 19 y 6 mo, mean 6 y 2 mo). In 19 children with profound visual impairment and four children with hemianopia (12 females, 11 males; age range 1 to 18 y, mean age 8 y 3 mo), evidence of perception of movement in the blind visual field was found and is described. Flash visual evoked potentials varied from no response to normal and was not correlated with visual behaviour. Recognition, detection, and use of this phenomenon in children is vital to their rehabilitation and interaction with their surroundings.
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ranking = 0.2
keywords = perception
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9/10. Cortical blindness after motorcycle accident: a case report.

    A 47 year-old Thai man presented with acute bilateral blindness after suffering head trauma in a motorcycle accident. No neurological deficit was found. The visual acuity was light perception with poor light projection on both eyes. Other ocular examinations were normal except ecchymosis on both lower eyelids and mild subconjunctival hemorrhage on the left eye. Emergency computerized tomography showed normal appearance of optic nerves, optic canals and multiple contusional intracerebral hemorrhages at both occipital lobes. This case demonstrated a rare condition of permanent cortical blindness without other neurological deficits resulting from a head trauma.
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ranking = 0.2
keywords = perception
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10/10. Cortical blindness.

    A 79-year-old woman with persistent cortical blindness caused by bilateral temporo-occipital infarctions was followed for 8 months. She had no light or visual motion perception. Our patient's visual imagery was intact, which was demonstrated when drawing elementary shapes; however, her drawing of objects was poor. Optokinetic nystagmus could not be elicited, but the vestibulo-ocular reflex (VOR) seemed intact. Although she was able to suppress her VOR by 'fixating' her outstretched hand which moved in phase with her head and body, she showed saccadic tracking eye movements in an attempt to visually 'follow' the self-generated movements of her outstretched hand, while her body and head were stationary. Such saccadic tracking seemed to be different from the previously described smooth tracking of self-moved targets by patients with acquired blindness caused by anterior visual pathway dysfunction.
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ranking = 0.2
keywords = perception
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