Abnormal white matter tractography of visual pathways detected by high-angular-resolution diffusion imaging (HARDI) corresponds to visual dysfunction in cortical/cerebral visual impairment

Visuospatial processing in early brain-based visual impairment is associated with differential recruitment of dorsal and ventral visual streams

Visuospatial processing impairments are prevalent in individuals with cerebral visual impairment (CVI) and are typically ascribed to "dorsal stream dysfunction" (DSD). However, the contribution of other cortical regions, including early visual cortex (EVC), frontal cortex, or the ventral visual stream, to such impairments remains unknown. Thus, here, we examined fMRI activity in these regions, while individuals with CVI (and neurotypicals) performed a visual search task within a dynamic naturalistic scene. First, behavioral performance was measured with eye tracking. Participants were instructed to search and follow a walking human target. CVI participants took significantly longer to find the target, and their eye gaze patterns were less accurate and less precise. Second, we used the same task in the MRI scanner. Along the dorsal stream, activation was reduced in CVI participants, consistent with the proposed DSD in CVI. Intriguingly, however, visual areas along the ventral stream showed the complete opposite pattern, with greater activation in CVI participants. In contrast, we found no differences in either EVC or frontal cortex between groups. These results suggest that the impaired visuospatial processing abilities in CVI are associated with differential recruitment of the dorsal and ventral visual streams, likely resulting from impaired selective attention.

Visual search patterns during exploration of naturalistic scenes are driven by saliency cues in individuals with cerebral visual impairment

We investigated the relative influence of image salience and image semantics during the visual search of naturalistic scenes, comparing performance in individuals with cerebral visual impairment (CVI) and controls with neurotypical development. Participants searched for a prompted target presented as either an image or text cue. Success rate and reaction time were collected, and gaze behavior was recorded with an eye tracker. A receiver operating characteristic (ROC) analysis compared the distribution of individual gaze landings based on predictions of image salience (using Graph-Based Visual Saliency) and image semantics (using Global Vectors for Word Representations combined with Linguistic Analysis of Semantic Salience) models. CVI participants were less likely and were slower in finding the target. Their visual search behavior was also associated with a larger visual search area and greater number of fixations. ROC scores were also lower in CVI compared to controls for both model predictions. Furthermore, search strategies in the CVI group were not affected by cue type, although search times and accuracy showed a significant correlation with verbal IQ scores for text-cued searches. These results suggest that visual search patterns in CVI are driven mainly by image salience and provide further characterization of higher-order processing deficits observed in this population.

Longitudinal neurological analysis of moderate and severe pediatric cerebral visual impairment

Introduction

Cerebral visual impairment (CVI) results from damage to cerebral visual processing structures. It is the most common cause of pediatric visual impairment in developed countries and rising in prevalence in developing nations. There is currently limited understanding on how neurologic, developmental, and ophthalmic factors predict outcome for pediatric CVI.

Method

A retrospective manual chart review of pediatric CVI patients seen at the tertiary pediatric hospital neurology and neuro-ophthalmology service between 2010 and 2019 was conducted. Patients were stratified into severity groups (based on a custom CVI grading score), and followed over time to identify outcome predictors. Collected baseline characteristics included perinatal, genetic, developmental, and neurologic history, along with neuroimaging and fundoscopic findings on examination. Longitudinal data collected included age, seizure control, and type of therapy received. Linear mixed-effect models were used for longitudinal CVI grade outcome analysis.

Results

A total of 249 individuals spanning 779 patient visits were identified. Mean age at diagnosis was 18.8 ± 16.8 months (2–108 months). About 64.3% were born at term age. Perinatal history revealed hypoxic ischemic encephalopathy (HIE) in 16.5%, intraventricular hemorrhage (IVH) in 11.6%, and seizures in 21.7%. At presentation, 60.3% had a diagnosis of cerebral palsy and 84.7% had developmental delay. Among all subjects, 78.6% had epilepsy; 33.8% had an epileptic encephalopathy, with spasms/hypsarrhythmia being most common. Abnormal neuroimaging was present in 93.8%. Genetic anomalies were present in 26.9%. Baseline visual examination revealed no blink-to-light (BTL) in 24.5%; only BTL in 34.5%, fixation/tracking in 26.5%, and optokinetic drum follow in 14.4%. Longitudinal data analysis showed that perinatal history of HIE, a positive epilepsy history, using multiple (≥3) epilepsy medications, cerebral palsy, and abnormal fundoscopic findings were all negatively associated with CVI grade change over time. After controlling for significant confounders, receiving any type of therapy [early childhood intervention (ECI), physical and occupational therapy (PT/OT), refractive error correction or glasses] was significantly associated with longitudinal improvement in CVI grade compared to patients who did not receive any therapy, with glasses yielding the largest benefit.

Conclusion

This study offers extensive insights into neurologic, developmental and ophthalmologic features in patients with moderate to severe CVI. In concordance with previous findings, aspects of perinatal history and epilepsy/seizure control may help inform severity and prognosis in the general neurology or ophthalmology clinic. Conversely, these aspects, as well as genetic and specific epilepsy traits may alert vision health care providers in the clinic to pursue visual evaluation in at-risk individuals. Longitudinal follow-up of CVI patients showed that interventional therapies demonstrated vision function improvement greater than no therapy and maturational development.

Neural correlates associated with impaired global motion perception in cerebral visual impairment (CVI)

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Cerebral visual impairment (CVI) is associated with impaired global motion processing.

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Mean motion coherence thresholds was higher in individuals with CVI.

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fMRI responses in area hMT+ showed an aberrant response profile in CVI.

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White matter tract reconstruction revealed cortico-cortical dysmyelination in CVI.

Cerebral visual impairment (CVI) is associated with a wide range of visual perceptual deficits including global motion processing. However, the underlying neurophysiological basis for these impairments remain poorly understood. We investigated global motion processing abilities in individuals with CVI compared to neurotypical controls using a combined behavioral and multi-modal neuroimaging approach. We found that CVI participants had a significantly higher mean motion coherence threshold (determined using a random dot kinematogram pattern simulating optic flow motion) compared to controls. Using functional magnetic resonance imaging (fMRI), we investigated activation response profiles in functionally defined early (i.e. primary visual cortex; area V1) and higher order (i.e. middle temporal cortex; area hMT+) stages of motion processing. In area V1, responses to increasing motion coherence were similar in both groups. However, in the CVI group, activation in area hMT+ was significantly reduced compared to controls, and consistent with a surround facilitation (rather than suppression) response profile. White matter tract reconstruction obtained from high angular resolution diffusion imaging (HARDI) revealed evidence of increased mean, axial, and radial diffusivities within cortico-cortical (i.e. V1-hMT+), but not thalamo-hMT+ connections. Overall, our results suggest that global motion processing deficits in CVI may be associated with impaired signal integration and segregation mechanisms, as well as white matter integrity at the level of area hMT+.

Exploratory Investigation of Brain MRI Lesions According to Whole Sample and Visual Function Subtyping in Children With Cerebral Visual Impairment

Background: There is limited research on brain lesions in children with cerebral visual impairment (CVI) of heterogeneous etiologies and according to associated subtyping and vision dysfunctions. This study was part of a larger project establishing data-driven subtypes of childhood CVI according to visual dysfunctions. Currently there is no consensus in relation to assessment, diagnosis and classification of CVI and more information about brain lesions may be of potential diagnostic value.

Aim: This study aimed to investigate overall patterns of brain lesions and associations with level of visual dysfunction and to compare the patterns between the classification subgroups in children with CVI.

Methods: School-aged children with CVI received ophthalmological and neuro-psychological/developmental assessments to establish CVI-related subtyping. Other pediatric information was collected from medical records. MRI scans were coded according to a semi-quantitative template including brain regions (right hemisphere, left hemisphere, visual pathways) and summed for total scores. Non-parametric analyses were conducted.

Results: 28 children had clinical brain MRI scans available [44% of total sample, Group A (lower severity of visual dysfunctions) n = 16, Group B (higher severity) n = 12]. Total brain scores ranged between 0 and 18 (Group A mdn = 7, IQR = 0.8–10.0, Group B mdn = 10, IQR = 6.5–11.8) and were widespread across regions. 71 per cent had post-geniculate visual pathway damage. The median total brain and hemisphere scores of Group B were higher than subgroup A but differences did not reach statistical significance. No statistically significant associations were found between brain scores and vision variables (acuity, contrast sensitivity).

Conclusion: This study found a spread of lesions across all regions on the brain scans in children with congenital CVI. The majority had damage in the postgeniculate visual pathways and visual cortex region suggesting this is an area of interest and potentially informative for diagnosis. However the subtyping classification did not show differences in number or region of lesions though the trend was higher toward Group B. This study confirms the complex diffuse and variable nature of brain lesions in children with congenital CVI, many of whom have other neurological impairments.

The relation between visual orienting functions, daily visual behaviour and visuoperceptual performance in children with (suspected) cerebral visual impairment

BACKGROUND

Children with cerebral visual impairment (CVI) present heterogeneous visual orienting functions (VOF) and higher-order perception. Multiple assessment methods evaluate CVI, but the relations between them remain unclear.

AIM

To investigate the relations between VOF and (1) daily life behaviour and (2) visuoperceptual tests in children with (suspected) CVI.

METHODS AND PROCEDURES

VOF were tested with a validated eye tracking-based paradigm. Visual perception was assessed using the children's visual impairment test for 3- to 6-year olds (CVIT 3-6) and (retrospective) visuoperceptual dimension results. Caregivers completed the Flemish cerebral visual impairment questionnaire (FCVIQ) and an expert panel scored relations between VOF and the other methods. We compared experts' survey responses with data-based results (linear mixed models and correlations).

OUTCOMES AND RESULTS

Fourty-four children (23 boys, 21 girls; median age = 7y11mo, SD = 2y7mo) participated. Twenty-one experts completed the survey. Slower VOF was significantly associated with (1) object and face processing impairments, (2) visual (dis)interest, (3) worse visual spatial perception (to local motion and form stimuli), and (4) worse CVIT 3-6 object and scene recognition (to cartoon stimuli).

CONCLUSIONS AND IMPLICATIONS

Integration of VOF with existing visual assessments provides a better clinical picture of CVI and can prevent misdiagnosing children as inattentive, incapable, or unmotivated.

Cortical Visual Impairments and Learning Disabilities

Medical advances in neonatology have improved the survival rate of premature infants, as well as children who are born under difficult neurological conditions. As a result, the prevalence of cerebral dysfunctions, whether minimal or more severe, is increasing in all industrialized countries and in some developing nations. Whereas in the past, ophthalmological diseases were considered principally responsible for severe visual impairment, today, all recent epidemiological studies show that the primary cause of blindness and severe visual impairment in children in industrialized countries is now neurological, with lesions acquired around the time of birth currently comprising the commonest contributor. The resulting cortical or cerebral visual impairments (CVIs) have long been ignored, or have been confused either with other ophthalmological disorders causing low vision, or with a range of learning disabilities. We present here the deleterious consequences that CVI can have upon learning and social interaction, and how these can be given behavioral labels without the underlying visual causes being considered. We discuss the need to train and inform clinicians in the identification and diagnosis of CVI, and how to distinguish the diagnosis of CVI from amongst other visual disorders, including the specific learning disorders. This is important because the range of approaches needed to enhance the development of children with CVI is specific to each child's unique visual needs, making incorrect labeling or diagnosis potentially detrimental to affected children because these needs are not met.

Early visual training and environmental adaptation for infants with visual impairment

AIM

To evaluate the effectiveness of early visual training and environmental adaptation on visual function and neurological development in infants with visual impairment.

METHOD

This was a pilot intervention clinical trial study. Thirty infants (mean age 5.9mo, SD 2.1mo, range 4-11mo; 16 males, 14 females) with peripheral visual impairment (PVI, n=15) or cerebral visual impairment (CVI, n=15) participated in a 6-month visual intervention programme. Thirty matched infants (mean age 6mo, SD 1.4mo, range 4-9mo; 18 males, 12 females) served as a comparison group. Primary outcome measures were visual acuity, contrast sensitivity, and qualitative ocular motor functions. Secondary outcomes were scores on the Griffiths Mental Developmental Scales (GMDS).

RESULTS

The treatment group showed a significant improvement in all the primary outcomes (p<0.01). The comparison group improved only in visual acuity and contrast sensitivity (p<0.01). The treatment group showed greater improvement than the comparison group in visual fixation (p=0.033) and smooth pursuit (p<0.01). The CVI subgroup showed greater improvement in visual acuity than the PVI subgroup (p<0.01). GMDS subscales of hand-eye coordination (p=0.01) and performance (p<0.01) increased in the treatment group, while the total score of the comparison group decreased, driven by language (p=0.039) and hand-eye coordination (p=0.025) subscales.

INTERPRETATION

Results suggest that, in infants with visual impairment, visual function and certain developmental outcomes improve in response to early visual training and environmental adaptation, in an interactive context. What this paper adds Early visual training and environmental adaptation are associated with enhanced visual acuity and smooth pursuit. Early visual training and environmental adaptation are associated with an improvement of neurological developmental outcome. Performance, hand-eye coordination, and language scores in Griffiths Mental Developmental Scales increase after visual training. After training, visual acuity improves more in infants with cerebral rather than anterior visual impairment. Type and complexity of visual impairment contribute to determine infants' response to training.

Anatomical Connectivity of the Visuospatial Attentional Network in Schizophrenia: A Diffusion Tensor Imaging Tractography Study

OBJECTIVE

In healthy individuals, the visuospatial attentional network consists of frontoparietal bundles; however, the anatomical organization of this network in persons with schizophrenia remains largely unknown. Using diffusion tensor imaging-based tractography, the authors investigated the white matter integrity and volume of frontoparietal and frontotemporo-occipital bundles in the right and left hemispheres and studied their structural asymmetry in persons with schizophrenia and in healthy individuals.

METHODS

This study included 34 participants with schizophrenia and 69 healthy individuals. Integrity parameters and volume were calculated in the three branches of the superior longitudinal fasciculus (SLF I, II, and III), the inferior longitudinal fasciculus, and the inferior fronto-occipital fasciculus in both hemispheres.

RESULTS

In the SLF II and SLF III of the right hemisphere, healthy individuals showed greater integrity, compared with participants with schizophrenia. Both groups presented increased integrity in the SLF III of the right hemisphere, compared with the SLF III of the left hemisphere, but only healthy individuals had this pattern regarding the SLF II. Bundle volumes did not differ between groups.

CONCLUSIONS

This study is the first to describe the structural hemispheric lateralization and organization of the visuospatial attentional network in persons with schizophrenia. The main findings indicate loss of integrity in the SLF II, associated with loss of asymmetry in participants with schizophrenia, compared with healthy individuals, suggesting a potential substrate of attentional deficits.

Cerebral Visual Impairment Characterized by Abnormal Visual Orienting Behavior With Preserved Visual Cortical Activation

Purpose

Children with cerebral visual impairment (CVI) often have abnormal visual orienting behaviors due to impaired or damaged visual cortex. Alternatively, visual-cortical function is intact but visual information is not transformed downstream into an appropriate oculomotor output (visuomotor dysfunction). We examined visual, anatomic, and oculomotor assessments to distinguish visuomotor dysfunction from CVI associated with severely reduced visual-cortical response.

Methods

We reviewed the medical records from children with CVI having abnormal visual orienting behaviors, normal ocular examinations, and born near term. Relevant data were visual evoked potentials (VEPs), Teller card acuity, eye movements recorded by video-oculography (VOG), and neuroimaging (magnetic resonance imaging [MRI]) including diffusion tensor imaging (DTI) tractography.

Results

Thirty subjects had visuomotor dysfunction based on a normal VEP; of these 33% had a normal MRI and 67% had white matter abnormalities associated with metabolic disease and/or decreased volume of brain parenchyma. VOG recordings showed smooth pursuit gains were uniformly reduced and saccades were dysmetric but followed the main sequence. Ten subjects had severe CVI based on VEPs at noise levels; visual acuities and MRI findings overlapped those of the visuomotor dysfunction group. Developmental delay, seizures, microcephaly, and hypotonia were common across all groups. All subjects with an abnormal conventional MRI had abnormal metrics on DTI tractography from the occipital lobe.

Conclusions

A subset of patients with CVI have abnormal visual orienting behaviors despite a normal VEP (visuomotor dysfunction). A majority have abnormal white matter metrics on tractography suggesting a downstream defect in sensorimotor transformation. Clinically, visuomotor dysfunction is indistinguishable from severe CVI.

Neuroplasticity in cerebral visual impairment (CVI): Assessing functional vision and the neurophysiological correlates of dorsal stream dysfunction

Cerebral visual impairment (CVI) results from perinatal injury to visual processing structures and pathways and is the most common individual cause of pediatric visual impairment and blindness in developed countries. While there is mounting evidence demonstrating extensive neuroplastic reorganization in early onset, profound ocular blindness, how the brain reorganizes in the setting of congenital damage to cerebral (i.e. retro-geniculate) visual pathways remains comparatively poorly understood. Individuals with CVI exhibit a wide range of visual deficits and, in particular, present with impairments of higher order visual spatial processing (referred to as "dorsal stream dysfunction") as well as object recognition (associated with processing along the ventral stream). In this review, we discuss the need for ongoing work to develop novel, neuroscience-inspired approaches to investigate functional visual deficits in this population. We also outline the role played by advanced structural and functional neuroimaging in helping to elucidate the underlying neurophysiology of CVI, and highlight key differences with regard to patterns of neural reorganization previously described in ocular blindness.

Cerebral Visual Impairment and Clinical Assessment: The European Perspective

This paper summarizes the multidisciplinary pediatric assessment methods of 3 European centers for identifying and assessing cerebral visual impairment in childhood. It describes a comprehensive neurodevelopmental assessment evaluation in which visual aspects play an important part. Developmental trajectories and the heterogeneity of the clinical picture are emphasized. Multidisciplinary ophthalmology and neurodisability/neurology teamwork together with the parent and teachers, to reach an integrated and individualized perspective for the individual child, are described. This comprehensive assessment is the starting point for habilitation programs and interventions, that can support and meet the child's needs and help them reach their optimal potential. Future developments in classification of the cerebral visual impairment conditions, building on the child's individual assessment profile, will further enhance the direction of clinical, educational, and research progress.

A Questionnaire Assessing What Teachers of the Visually Impaired Know About Cortical/Cerebral Vision Impairment

Cortical/cerebral visual impairment (CVI) is now the main cause of visual impairment in developed countries, yet it remains poorly understood. Four hundred and ninteen teachers of the visually impaired (TVIs) from across the United States responded to a questionnaire targeted at evaluating the preparedness of TVIs to serve their students with CVI. The TVIs were asked about their background knowledge, their abilities to assess a student with CVI, and their abilities to apply what they know to best help their students. The primary finding was that there is a perceived unmet need for TVIs to receive formal training in CVI during their certification. The results of this survey provide a foundation for future research on CVI knowledge and education among TVIs.

Targeted panel sequencing identifies a novel NR2F1 mutations in a patient with Bosch-Boonstra-Schaaf optic atrophy syndrome

Background: Nuclear hormone receptor gene, NR2F1, plays a key role in brain and eye development. Bosch-Boonstra-Schaaf optic atrophy syndrome (BBSOAS, MIM #615772) is an autosomal dominant hereditary disorder caused by mutations in this gene. However, there have been few studies describing fundus and optical coherence tomography findings on BBSOAS. Materials and methods: The patient underwent a detailed clinical evaluation and ophthalmic imaging followed by targeted panel next-generation sequencing analysis. Results: A 7-year-old Korean boy, with a history of delayed development and borderline intellectual functioning, was referred to our clinic for evaluation of low vision. He was born full-term with no perinatal insults. Best-corrected visual acuity was 20/100 in both eyes, and latent nystagmus was noted. Dilated fundus examinations revealed optic atrophy in both eyes, and optical coherence tomography showed diffuse thinning of retinal nerve fiber layers. Targeted panel next-generation sequencing showed novel c.513C>G; p.Tyr171Ter (NM_005654.4) in NR2F1 gene. This stop-gain mutation was predicted to be deleterious by in silico prediction programs, and was absent in the current population genomic database. Conclusions: We highlighted the value of genetic testing in definite diagnosis of BBSOAS in patients with unexplained optic atrophy.

Is there consensus in defining childhood cerebral visual impairment? A systematic review of terminology and definitions

The childhood condition of visual difficulties caused by brain damage, commonly termed cortical or cerebral visual impairment (CVI), is well established but has no internationally accepted definition. Clarification of its core features is required to advance research and clinical practice. This systematic review aimed to identify the definitions of childhood CVI in the original scientific literature to describe and critically appraise a consensual definition of the condition. MEDLINE, EMBASE, PsychINFO, CINAHL and AMED databases were searched in January 2017. Studies were included if they (1) were published original research, (2) contained a childhood CVI sample, (3) contained a definition of CVI and (4) described their CVI identification/diagnostic method. Thematic analysis identified concepts within definitions and narrative synthesis was conducted. Of 1150 articles, 51 met inclusion criteria. Definitions were subdivided according to detail (descriptive definition, description not reaching definition status and diagnostic/operationalising criteria). Three themes concerning visual deficits, eye health and brain integrity were identified (each containing subthemes) and analysed individually across definitions. The most common themes were ‘visual impairment’ (n=20), ‘retrochiasmatic pathway damage’(n=13) and ‘normal/near normal eye health’ (n=15). The most consensual definition identified here may not be the best quality for advancing our understanding of CVI. We argue for the alternative definition: CVI is a verifiable visual dysfunction which cannot be attributed to disorders of the anterior visual pathways or any potentially co-occurring ocular impairment. We propose reporting guidelines to permit comparison across studies and increase the evidence base for more reliable clinical assessment and diagnosis.

Prognostic significance of intraoperative change in the fractional anisotropy and the volume of the optic chiasma during resection of suprasellar tumors

OBJECTIVE The aim of this study was to test the prognostic significance of intraoperative changes in the fractional anisotropy (FA) and the volume of the optic chiasma and their correlation with visual outcome. METHODS Twenty-eight sequential patients with suprasellar tumors presenting with chiasma compression syndrome were surgically treated under intraoperative MRI control between March 2014 and July 2016. The FA and the volume of the optic chiasma were measured immediately before and immediately after tumor resection. The visual impairment score (VIS) was used to quantify the severity of the ophthalmological disturbances before surgery, 10-14 days after surgery, and again 3 months thereafter. The change in the FA and the volume of the optic chiasma was correlated to the improvement of vision. The correlation between other predictors such as the age of the patients and the duration of symptoms and the visual outcome was tested. RESULTS The VIS improved significantly after surgery. The FA values of the optic chiasma decreased significantly after decompression, whereas the volume of the optic chiasma increased significantly after decompression. The early and delayed improvement of vision was strongly correlated to the decrease in the average FA and the increase of the volume of the optic chiasma. The duration of symptoms showed a significant negative correlation to the visual outcome. However, the decrease in the FA showed the strongest correlation to the improvement of the VIS, followed by the expansion of the optic chiasma, and then the duration of symptoms. CONCLUSIONS The decrease in the FA and the expansion of the optic chiasma after its decompression are strong early predictors of the visual outcome. These parameters are also able to predict delayed improvement of vision.

Disentangling How the Brain is "Wired" in Cortical (Cerebral) Visual Impairment

Cortical (cerebral) visual impairment (CVI) results from perinatal injury to visual processing structures and pathways of the brain and is the most common cause of severe visual impairment or blindness in children in developed countries. Children with CVI display a wide range of visual deficits including decreased visual acuity, impaired visual field function, as well as impairments in higher-order visual processing and attention. Together, these visual impairments can dramatically influence a child's development and well-being. Given the complex neurologic underpinnings of this condition, CVI is often undiagnosed by eye care practitioners. Furthermore, the neurophysiological basis of CVI in relation to observed visual processing deficits remains poorly understood. Here, we present some of the challenges associated with the clinical assessment and management of individuals with CVI. We discuss how advances in brain imaging are likely to help uncover the underlying neurophysiology of this condition. In particular, we demonstrate how structural and functional neuroimaging approaches can help gain insight into abnormalities of white matter connectivity and cortical activation patterns, respectively. Establishing a connection between how changes within the brain relate to visual impairments in CVI will be important for developing effective rehabilitative and education strategies for individuals living with this condition.

Cerebral versus Ocular Visual Impairment: The Impact on Developmental Neuroplasticity

Cortical/cerebral visual impairment (CVI) is clinically defined as significant visual dysfunction caused by injury to visual pathways and structures occurring during early perinatal development. Depending on the location and extent of damage, children with CVI often present with a myriad of visual deficits including decreased visual acuity and impaired visual field function. Most striking, however, are impairments in visual processing and attention which have a significant impact on learning, development, and independence. Within the educational arena, current evidence suggests that strategies designed for individuals with ocular visual impairment are not effective in the case of CVI. We propose that this variance may be related to differences in compensatory neuroplasticity related to the type of visual impairment, as well as underlying alterations in brain structural connectivity. We discuss the etiology and nature of visual impairments related to CVI, and how advanced neuroimaging techniques (i.e., diffusion-based imaging) may help uncover differences between ocular and cerebral causes of visual dysfunction. Revealing these differences may help in developing future strategies for the education and rehabilitation of individuals living with visual impairment.

A preliminary study of the clinical application of optic pathway diffusion tensor tractography in suprasellar tumor surgery: preoperative, intraoperative, and postoperative assessment

OBJECT

Visual impairments are the most common objective manifestations of suprasellar lesions. Diffusion tensor imaging (DTI) is a noninvasive MRI modality that depicts the subcortical white matter tracts in vivo. In this study the authors tested the value of visual pathway tractography in comparison with visual field and visual acuity analyses.

METHODS

This prospective study consisted of 25 patients with progressive visual impairment due to suprasellar mass lesions and 6 control patients with normal vision without such lesions. Visual acuity, visual field, and the optic fundus were examined preoperatively and repeated 1 week and 3 months after surgery. Visual pathway DTI tractography was performed preoperatively, intraoperatively immediately after tumor resection, and 1 week and 3 months after surgery.

RESULTS

In the control group, pre- and postoperative visual status were normal and visual pathway tractography revealed fibers crossing the optic chiasm without any alteration. In patients with suprasellar lesions, vision improved in 24 of 25. The mean distance between optic tracts in tractography decreased after tumor resection and detectable fibers crossing the optic chiasm increased from 12% preoperatively to 72% postoperatively 3 months after tumor resection, and undetectable fibers crossing the optic chiasm decreased from 88% preoperatively to 27% postoperatively 3 months after tumor resection. Visual improvement after tumor removal 1 week and 3 months after surgery was significantly correlated with the distance between optic tracts in intraoperative tractography (p < 0.01).

CONCLUSIONS

Visual pathway DTI tractography appears to be a promising adjunct to the standard clinical and paraclinical visual examinations in patients with suprasellar mass lesions. The intraoperative findings, in particular the distance between optic tract fibers, can predict visual outcome after tumor resection. Furthermore, postoperative application of this technique may be useful in following anterior optic pathway recovery.

Using structural and functional brain imaging to uncover how the brain adapts to blindness

Advances in neuroimaging technology have been instrumental in uncovering the dramatic neurological changes that result from blindness, as well as revealing the inner workings of the human brain. Specifically, modern imaging techniques enable us to examine how the brain adapts and "re-wires" itself as a result of changes in behavior, the environment, injury, or disease; a process referred to as neuroplasticity. Following an overview of commonly employed neuroimaging techniques, we discuss structural and functional neuroplastic brain changes associated with profound visual deprivation. In particular, we highlight how associated structural changes often occur within areas that process intact senses (such as hearing, touch, and smell) while functional changes tend to implicate areas of the brain normally ascribed to the processing of visual information. Evidence will primarily focus on profound blindness due to ocular cause, but related work in cerebral/cortical visual impairment (CVI) will also be discussed. The potential importance of these findings within the context of education and rehabilitation is proposed.