Contrast Medium-Induced Transient Cortical Blindness: A Systematic Review of the Literature.

PURPOSE: To summarize identified risk factors, the most common clinical presentations, radiological and neurophysiological features, and proposed pathophysiological mechanisms of contrast medium-induced transient cortical blindness (TCB). METHODS: A systematic search of PubMed, Cochrane Central Register of Controlled Trials, and clinicaltrials.gov was performed. A total of 115 patients from 2 retrospective cohort studies, 10 case series, and 52 case reports were included. RESULTS: The available evidence suggests that TCB can manifest after both invasive and noninvasive contrast-enhanced procedures. The pathophysiology of TCB is unclear; however, the primary mechanism suggested involves the direct neurotoxic effect of the contrast medium. Ionic, nonionic, hyperosmolar, isoosmolar, and even ethiodized oil have been implicated. Imaging findings are nonspecific, and absent in about half of patients. Onset is within 30 minutes in about half of patients and resolves within 1 day in about half of patients, but delayed onset after a day and delayed resolution after a week may occur. Higher contrast medium dosage and its injection solely into the posterior circulation were the only risk factors identified in association with TCB. CONCLUSIONS: TCB is a rare, idiopathic, and typically self-limited condition associated with direct posterior cerebral neurotoxicity of iodinated contrast media, and appears to be dose-dependent.

Multisensory Integration and the Society for Neuroscience: Then and Now.

The operation of our multiple and distinct sensory systems has long captured the interest of researchers from multiple disciplines. When the Society was founded 50 years ago to bring neuroscience research under a common banner, sensory research was largely divided along modality-specific lines. At the time, there were only a few physiological and anatomical observations of the multisensory interactions that powerfully influence our everyday perception. Since then, the neuroscientific study of multisensory integration has increased exponentially in both volume and diversity. From initial studies identifying the overlapping receptive fields of multisensory neurons, to subsequent studies of the spatial and temporal principles that govern the integration of multiple sensory cues, our understanding of this phenomenon at the single-neuron level has expanded to include a variety of dimensions. We now can appreciate how multisensory integration can alter patterns of neural activity in time, and even coordinate activity among populations of neurons across different brain areas. There is now a growing battery of sophisticated empirical and computational techniques that are being used to study this process in a number of models. These advancements have not only enhanced our understanding of this remarkable process in the normal adult brain, but also its underlying circuitry, requirements for development, susceptibility to malfunction, and how its principles may be used to mitigate malfunction.

Functional preservation and enhanced capacity for visual restoration in subacute occipital stroke.

Stroke damage to the primary visual cortex (V1) causes a loss of vision known as hemianopia or cortically-induced blindness. While perimetric visual field improvements can occur spontaneously in the first few months post-stroke, by 6 months post-stroke, the deficit is considered chronic and permanent. Despite evidence from sensorimotor stroke showing that early injury responses heighten neuroplastic potential, to date, visual rehabilitation research has focused on patients with chronic cortically-induced blindness. Consequently, little is known about the functional properties of the post-stroke visual system in the subacute period, nor do we know if these properties can be harnessed to enhance visual recovery. Here, for the first time, we show that 'conscious' visual discrimination abilities are often preserved inside subacute, perimetrically-defined blind fields, but they disappear by ∼6 months post-stroke. Complementing this discovery, we now show that training initiated subacutely can recover global motion discrimination and integration, as well as luminance detection perimetry, just as it does in chronic cortically-induced blindness. However, subacute recovery was attained six times faster; it also generalized to deeper, untrained regions of the blind field, and to other (untrained) aspects of motion perception, preventing their degradation upon reaching the chronic period. In contrast, untrained subacutes exhibited spontaneous improvements in luminance detection perimetry, but spontaneous recovery of motion discriminations was never observed. Thus, in cortically-induced blindness, the early post-stroke period appears characterized by gradual-rather than sudden-loss of visual processing. Subacute training stops this degradation, and is far more efficient at eliciting recovery than identical training in the chronic period. Finally, spontaneous visual improvements in subacutes were restricted to luminance detection; discrimination abilities only recovered following deliberate training. Our findings suggest that after V1 damage, rather than waiting for vision to stabilize, early training interventions may be key to maximize the system's potential for recovery.

Factors Associated With Lack of Vision Improvement in Children With Cortical Visual Impairment.

BACKGROUND: Improvement in vision has been noted in children with cortical visual impairment (CVI), resulting from disparate types of brain injury. The purpose of our study was to determine the risk factors associated with poor recovery of vision in this group of patients. METHODS: Case records of children who were born before 2010 with at least 4 follow-up visits for CVI were reviewed for underlying etiologies of CVI, visual acuity (VA), and associated neurological and ophthalmological disorders. VA was assessed in 6 qualitative grades. Changes in VA were recorded as the difference between the grades of VA at presentation and the last follow-up visit. The outcome was calculated as a ratio of actual improvement to potential improvement in grades of qualitative VA. Multiple linear regression determined factors associated with lack of vision improvement in all children and based on etiology. RESULTS: Fifty-three children with CVI were identified. The median age at presentation was 13.6 months (range: 2.9-76.4 months) and the median follow-up was 5.8 years (1.1-16.3 years). CVI resulted from central nervous system (CNS) malformation (9.4%), hypoxic/inflammatory injury (15.1%), seizures (24.5%), and combined causes (51.0%). Vision improvement was noted in 83% of children. Lack of VA improvement was associated with older age at presentation in all children with CVI and within each etiological group except CNS malformation. None of the other investigated variables were associated with poor recovery of VA. CONCLUSIONS: Most of the children with CVI showed improvement in vision. Older age at presentation, but not etiology of CVI, was associated with poor improvement in VA.

Patterns of Cortical Visual Field Defects From Embolic Stroke Explained by the Anastomotic Organization of Vascular Microlobules.

The cerebral cortex is supplied by vascular microlobules, each comprised of a half dozen penetrating arterioles that surround a central draining venule. The surface arterioles that feed the penetrating arterioles are interconnected via an extensively anastomotic plexus. Embolic occlusion of a small surface arteriole rarely produces a local infarct, because collateral blood flow is available through the vascular reticulum. Collateral flow also protects against infarct after occlusion of a single penetrating arteriole. Cortical infarction requires blockage of a major arterial trunk, with arrest of blood flow to a relatively large vascular territory. For striate cortex, the major vessels compromised by emboli are the inferior calcarine and superior calcarine arteries, as well as the distal branches of the middle cerebral artery. Their vascular territories have a fairly consistent relationship with the retinotopic map. Consequently, occlusion by emboli results in stereotypical visual field defects. The organization of the arterial supply to the occipital lobe provides an anatomical explanation for a phenomenon that has long puzzled neuro-ophthalmologists, namely, that of the myriad potential patterns of cortical visual field loss, only a few are encountered commonly from embolic cortical stroke.

Visual and Motor Recovery After "Cognitive Therapeutic Exercises" in Cortical Blindness: A Case Study.

BACKGROUND AND PURPOSE: Spontaneous visual recovery is rare after cortical blindness. While visual rehabilitation may improve performance, no visual therapy has been widely adopted, as clinical outcomes are variable and rarely translate into improvements in activities of daily living (ADLs). We explored the potential value of a novel rehabilitation approach "cognitive therapeutic exercises" for cortical blindness. CASE DESCRIPTION: The subject of this case study was 48-year-old woman with cortical blindness and tetraplegia after cardiac arrest. Prior to the intervention, she was dependent in ADLs and poorly distinguished shapes and colors after 19 months of standard visual and motor rehabilitation. Computed tomographic images soon after symptom onset demonstrated acute infarcts in both occipital cortices. INTERVENTION: The subject underwent 8 months of intensive rehabilitation with "cognitive therapeutic exercises" consisting of discrimination exercises correlating sensory and visual information. OUTCOMES: Visual fields increased; object recognition improved; it became possible to watch television; voluntary arm movements improved in accuracy and smoothness; walking improved; and ADL independence and self-reliance increased. Subtraction of neuroimaging acquired before and after rehabilitation showed that focal glucose metabolism increases bilaterally in the occipital poles. DISCUSSION: This study demonstrates feasibility of "cognitive therapeutic exercises" in an individual with cortical blindness, who experienced impressive visual and sensorimotor recovery, with marked ADL improvement, more than 2 years after ischemic cortical damage.Video Abstract available for additional insights from the authors (see Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A173).

Hypoxic-Ischemic Encephalopathy With Clinical and Imaging Abnormalities Limited to Occipital Lobe.

BACKGROUND: The vulnerable brain areas in hypoxic-ischemic encephalopathy (HIE) following systemic hypotension are typically the neocortex, deep cerebral gray nuclei, hippocampus, cerebellum, and the parieto-occipital arterial border zone region. The visual cortex is not commonly recognized as a target in this setting. METHODS: Single-institution review from 2007 to 2015 of patients who suffered cortical visual loss as an isolated clinical manifestation following systemic hypotension and whose brain imaging showed abnormalities limited to the occipital lobe. RESULTS: Nine patients met inclusion criteria. Visual loss at outset ranged from hand movements to 20/20, but all patients had homonymous field loss at best. In 1 patient, imaging was initially normal but 4 months later showed encephalomalacia. In 2 patients, imaging was initially subtle enough to be recognized as abnormal only when radiologists were advised that cortical visual loss was present. CONCLUSIONS: The occipital lobe may be an isolated target in HIE with cortical visual loss as the only clinical manifestation. Imaging performed in the acute period may appear normal or disclose abnormalities subtle enough to be overlooked. Radiologists informed of the clinical manifestations may be more attune to these abnormalities, which will become more apparent months later when occipital volume loss develops.

Beyond blindsight: properties of visual relearning in cortically blind fields.

Damage to the primary visual cortex (V1) or its immediate afferents results in a dense scotoma, termed cortical blindness (CB). CB subjects have residual visual abilities, or blindsight, which allow them to detect and sometimes discriminate stimuli with high temporal and low spatial frequency content. Recent work showed that with training, discriminations in the blind field can become more reliable, and even reach consciousness. However, the narrow spatiotemporal bandwidth of blindsight limits its functional usefulness in everyday vision. Here, we asked whether visual training can induce recovery outside the spatiotemporal bandwidth of blindsight. Specifically, could human CB subjects learn to discriminate static, nonflickering stimuli? Can such learning transfer to untrained stimuli and tasks, and does double training with moving and static stimuli provide additional advantages relative to static training alone? We found CB subjects capable of relearning static orientation discriminations following single as well as double training. However, double training with complex, moving stimuli in a separate location was necessary to recover complex motion thresholds at locations trained with static stimuli. Subjects trained on static stimuli alone could only discriminate simple motion. Finally, both groups had approximately equivalent, incomplete recovery of fine orientation and direction discrimination thresholds, as well as contrast sensitivity. These results support two conclusions: (1) from a practical perspective, complex moving stimuli and double training may be superior training tools for inducing visual recovery in CB, and (2) the cortically blind visual system can relearn to perform a wider range of visual discriminations than predicted by blindsight alone.

Connectivity between the superior colliculus and the amygdala in humans and macaque monkeys: virtual dissection with probabilistic DTI tractography.

It has been suggested that some cortically blind patients can process the emotional valence of visual stimuli via a fast, subcortical pathway from the superior colliculus (SC) that reaches the amygdala via the pulvinar. We provide in vivo evidence for connectivity between the SC and the amygdala via the pulvinar in both humans and rhesus macaques. Probabilistic diffusion tensor imaging tractography revealed a streamlined path that passes dorsolaterally through the pulvinar before arcing rostrally to traverse above the temporal horn of the lateral ventricle and connect to the lateral amygdala. To obviate artifactual connectivity with crossing fibers of the stria terminalis, the stria was also dissected. The putative streamline between the SC and amygdala traverses above the temporal horn dorsal to the stria terminalis and is positioned medial to it in humans and lateral to it in monkeys. The topography of the streamline was examined in relation to lesion anatomy in five patients who had previously participated in behavioral experiments studying the processing of emotionally valenced visual stimuli. The pulvinar lesion interrupted the streamline in two patients who had exhibited contralesional processing deficits and spared the streamline in three patients who had no deficit. Although not definitive, this evidence supports the existence of a subcortical pathway linking the SC with the amygdala in primates. It also provides a necessary bridge between behavioral data obtained in future studies of neurological patients, and any forthcoming evidence from more invasive techniques, such as anatomical tracing studies and electrophysiological investigations only possible in nonhuman species.

Transient increase of intact visual field size by high-frequency narrow-band stimulation.

Three patients with visual field defects were stimulated with a square matrix pattern, either static, or flickering at frequencies that had been found to either promote or not promote blindsight performance. Comparison between pre- and post-stimulation perimetric maps revealed an increase in the size of the intact visual field but only for flicker frequencies previously found to promote blindsight. These changes were temporary but dramatic - in two instances the intact field was increased by an area of ∼30 deg(2) of visual angle. These results indicate that not only does specific high-frequency stimulus flicker promote blindsight, but that intact visual field size may be increased by stimulation at the same frequencies. Our findings inform speculation on both the brain mechanisms and the potency of temporal modulation for altering the functional visual field.

From affective blindsight to emotional consciousness.

Following destruction or denervation of the primary visual cortex (V1) cortical blindness ensues. Affective blindsight refers to the uncanny ability of such patients to respond correctly, or above chance level, to visual emotional expressions presented to their blind fields. Fifteen years after its original discovery, affective blindsight still fascinates neuroscientists and philosophers alike, as it offers a unique window on the vestigial properties of our visual system that, though present in the intact brain, tend to be unnoticed or even actively inhibited by conscious processes. Here we review available studies on affective blindsight with the intent to clarify its functional properties, neural bases and theoretical implications. Evidence converges on the role of subcortical structures of old evolutionary origin such as the superior colliculus, the pulvinar and the amygdala in mediating affective blindsight and nonconscious perception of emotions. We conclude that approaching consciousness, and its absence, from the vantage point of emotion processing may uncover important relations between the two phenomena, as consciousness may have evolved as an evolutionary specialization to interact with others and become aware of their social and emotional expressions.

Transient cortical visual impairment after video-assisted thoracic surgery: a case report.

BACKGROUND: Visual loss associated with thoracic surgery has been reported mostly after coronary angiography or bypass surgery. The position of video-assisted thoracic surgery (VATS) is usually lateral, thus not compressive to the globe. Visual loss after VATS has not been reported. Herein we report a patient without any cardiovascular risk factors who experienced transient cortical blindness after an uneventful VATS. CASE PRESENTATION: A 40-year-old man noticed a visual loss at the recovery room after VATS. He showed normal pupillary reflex, normal optic disc appearance, and homonymous hemianopia respecting the vertical meridian, thus was typical for cortical visual impairment. CONCLUSIONS: Transient cortical visual impairment could be encountered after an uneventful VATS in a patient without any cardiovascular risk factors.

Visual recovery in cortical blindness is limited by high internal noise.

Damage to the primary visual cortex typically causes cortical blindness (CB) in the hemifield contralateral to the damaged hemisphere. Recent evidence indicates that visual training can partially reverse CB at trained locations. Whereas training induces near-complete recovery of coarse direction and orientation discriminations, deficits in fine motion processing remain. Here, we systematically disentangle components of the perceptual inefficiencies present in CB fields before and after coarse direction discrimination training. In seven human CB subjects, we measured threshold versus noise functions before and after coarse direction discrimination training in the blind field and at corresponding intact field locations. Threshold versus noise functions were analyzed within the framework of the linear amplifier model and the perceptual template model. Linear amplifier model analysis identified internal noise as a key factor differentiating motion processing across the tested areas, with visual training reducing internal noise in the blind field. Differences in internal noise also explained residual perceptual deficits at retrained locations. These findings were confirmed with perceptual template model analysis, which further revealed that the major residual deficits between retrained and intact field locations could be explained by differences in internal additive noise. There were no significant differences in multiplicative noise or the ability to process external noise. Together, these results highlight the critical role of altered internal noise processing in mediating training-induced visual recovery in CB fields, and may explain residual perceptual deficits relative to intact regions of the visual field.

Anton-Babinski syndrome in an old patient: a case report and literature review.

Anton-Babinski syndrome is a rare disease featuring bilateral cortical blindness and anosognosia with visual confabulation, but without dementia or any memory impairment. It has a unique neuropsychiatric presentation and should be highly suspected in those with odd visual loss and imaging evidence of occipital lobe injury. In the case discussed herein, a 90-year-old man presented with bilateral blindness, obvious anosognosia, and vivid visual confabulation, which he had had for 3 days. Brain computed tomography demonstrated recent hypodense infarctions at the bilateral occipital lobes. Thus, the patient was diagnosed with Anton-Babinski syndrome. Because of his age and the thrombolytic therapy during the golden 3 hours after ischemic stroke, the patient received aspirin therapy rather than tissue plasminogen activator or warfarin. He gradually realized he was blind during the following week, but died of pneumonia 1 month later. In the literature, it is difficult to establish awareness of blindness in patients with Anton-Babinski syndrome, but optimistically, in one report, a patient was aware of blindness within 2 weeks, without vision improvement. Our case illustrates that elderly patients with Anton-Babinski syndrome can partially recover and that 1 week is the shortest time for the establishment of awareness of blindness for sufferers without vision improvement.

Visually evoked responses in extrastriate area MT after lesions of striate cortex in early life.

Lesions of striate cortex [primary visual cortex (V1)] in adult primates result in blindness. In contrast, V1 lesions in neonates typically allow much greater preservation of vision, including, in many human patients, conscious perception. It is presently unknown how this marked functional difference is related to physiological changes in cortical areas that are spared by the lesions. Here we report a study of the middle temporal area (MT) of adult marmoset monkeys that received unilateral V1 lesions within 6 weeks of birth. In contrast with observations after similar lesions in adult monkeys, we found that virtually all neurons in the region of MT that was deprived of V1 inputs showed robust responses to visual stimulation. These responses were very similar to those recorded in neurons with receptive fields outside the lesion projection zones in terms of firing rate, signal-to-noise ratio, and latency. In addition, the normal retinotopic organization of MT was maintained. Nonetheless, we found evidence of a very specific functional deficit: direction selectivity, a key physiological characteristic of MT that is known to be preserved in many cells after adult V1 lesions, was absent. These results demonstrate that lesion-induced reorganization of afferent pathways is sufficient to develop robust visual function in primate extrastriate cortex, highlighting a likely mechanism for the sparing of vision after neonatal V1 lesions. However, they also suggest that interactions with V1 in early postnatal life are critical for establishing stimulus selectivity in MT.

Amygdala activation for eye contact despite complete cortical blindness.

Cortical blindness refers to the loss of vision that occurs after destruction of the primary visual cortex. Although there is no sensory cortex and hence no conscious vision, some cortically blind patients show amygdala activation in response to facial or bodily expressions of emotion. Here we investigated whether direction of gaze could also be processed in the absence of any functional visual cortex. A well-known patient with bilateral destruction of his visual cortex and subsequent cortical blindness was investigated in an fMRI paradigm during which blocks of faces were presented either with their gaze directed toward or away from the viewer. Increased right amygdala activation was found in response to directed compared with averted gaze. Activity in this region was further found to be functionally connected to a larger network associated with face and gaze processing. The present study demonstrates that, in human subjects, the amygdala response to eye contact does not require an intact primary visual cortex.

S-cone psychophysics.

We review the features of the S-cone system that appeal to the psychophysicist and summarize the celebrated characteristics of S-cone mediated vision. Two factors are emphasized: First, the fine stimulus control that is required to isolate putative visual mechanisms and second, the relationship between physiological data and psychophysical approaches. We review convergent findings from physiology and psychophysics with respect to asymmetries in the retinal wiring of S-ON and S-OFF visual pathways, and the associated treatment of increments and decrements in the S-cone system. Beyond the retina, we consider the lack of S-cone projections to superior colliculus and the use of S-cone stimuli in experimental psychology, for example to address questions about the mechanisms of visually driven attention. Careful selection of stimulus parameters enables psychophysicists to produce entirely reversible, temporary, "lesions," and to assess behavior in the absence of specific neural subsystems.