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

Methodological considerations on diffusion MRI tractography in infants aged 0-2 years: a scoping review

Diffusion MRI (dMRI) enables studying the complex architectural organization of the brain's white matter (WM) through virtual reconstruction of WM fiber tracts (tractography). Despite the anticipated clinical importance of applying tractography to study structural connectivity and tract development during the critical period of rapid infant brain maturation, detailed descriptions on how to approach tractography in young infants are limited. Over the past two decades, tractography from infant dMRI has mainly been applied in research settings and focused on diffusion tensor imaging (DTI). Only few studies used techniques superior to DTI in terms of disentangling information on the brain's organizational complexity, including crossing fibers. While more advanced techniques may enhance our understanding of the intricate processes of normal and abnormal brain development and extensive knowledge has been gained from application on adult scans, their applicability in infants has remained underexplored. This may partially be due to the higher technical requirements versus the need to limit scan time in young infants. We review various previously described methodological practices for tractography in the infant brain (0-2 years-of-age) and provide recommendations to optimize advanced tractography approaches to enable more accurate reconstructions of the brain WM's complexity. IMPACT: Diffusion tensor imaging is the technique most frequently used for fiber tracking in the developing infant brain but is limited in capability to disentangle the complex white matter organization. Advanced tractography techniques allow for reconstruction of crossing fiber bundles to better reflect the brain's complex organization. Yet, they pose practical and technical challenges in the fast developing young infant's brain. Methods on how to approach advanced tractography in the young infant's brain have hardly been described. Based on a literature review, recommendations are provided to optimize tractography for the developing infant brain, aiming to advance early diagnosis and neuroprotective strategies.

Childhood cerebral visual impairment subtype classification based on an extensive versus a limited test battery

Purpose

To classify CVI subtypes and compare the added value of an extensive test battery over a limited test battery in subtype classification of cerebral visual impairment (CVI) in children.

Methods

Seventy-five children with a clinical diagnosis of CVI (median [IQR] age: 9 [7-12] years) were identified from the medical records. The extensive test battery included visual acuity, contrast sensitivity, ocular alignment, eye movement analysis, visual field analysis, optic nerve head evaluation, and evaluation of visual perception. The limited test battery included visual acuity, contrast sensitivity, ocular alignment, and evaluation of visual perception. Principal component analysis (PCA) followed by cluster analysis was done, for both test batteries separately, to determine the optimum subtype classification for CVI.

Results

Fifty-one participants with an extensive test battery with mild to moderate visual impairment were included in the main analysis. This resulted in four CVI subtypes for the extensive test battery (subtle characteristics, higher-level visual function deficits, lower-level visual function deficits, and higher- and lower- level visual function deficits) and three CVI subtypes for the limited test battery (subtle characteristics, higher-level visual function deficits, and higher- and lower- level visual function deficits). There were significant differences between the subtypes for 9 out of 10 measures of the extensive and all 4 measures of the limited test battery (p < 0.05). The subtle characteristics subtype (extensive n = 19, limited n = 15) showed near normal lower and higher-level visual functions in both test batteries. The higher-level visual function deficits subtype (extensive n = 18, limited n = 24) showed near normal visual acuity combined with significant visual perceptual deficits in both test batteries; accompanied by visual pathways defects and abnormal eye movement behavior in the extensive test battery. The higher- and lower- level visual function deficits subtype (extensive n = 4, limited n = 12) showed both higher and lower-level visual function deficits in both test batteries, but application of the extensive test battery revealed additional visual pathways defects and abnormal eye movement behavior. The lower-level visual function deficits CVI subtype (extensive n = 10) was a new subtype identified by the extensive test battery. This subtype showed lower-level visual function deficits together with abnormal eye movement measures.

Conclusion

This data-driven study has provided meaningful CVI subtype classifications based on the outcomes of various key functional and structural measures in CVI diagnosis. Comparison of the extensive test battery to the limited test battery revealed the added value of an extensive test battery in classifying CVI. The outcomes of this study, therefore, have provided a new direction in the area of CVI classification.

Pediatric abusive head trauma: visual outcomes, evoked potentials, diffusion tensor imaging, and relationships to retinal hemorrhages

PURPOSE

Function and anatomy of the visual system were evaluated in children with abusive head trauma (AHT). The relationships between retinal hemorrhages at presentation were examined with outcome measures.

METHODS

Retrospective review of data in children with AHT for 1) visual acuity at last follow-up, 2) visual evoked potentials (VEP) after recovery, 3) diffusion metrics of white matter tracts and grey matter within the occipital lobe on diffusion tensor imaging (DTI), and 4) patterns of retinal hemorrhages at presentation. Visual acuity was converted into logarithm of minimum angle of resolution (logMAR) after correction for age. VEPs were also scored by objective signal-to-noise ratio (SNR).

RESULTS

Of 202 AHT victims reviewed, 45 met inclusion criteria. Median logMAR was reduced to 0.8 (approximately 20/125 Snellen equivalent), with 27% having no measurable vision. Thirty-two percent of subjects had no detectable VEP signal. VEPs were significantly reduced in subjects initially presenting with traumatic retinoschisis or hemorrhages involving the macula (p < 0.01). DTI tract volumes were decreased in AHT subjects compared to controls (p < 0.001). DTI metrics were most affected in AHT victims showing macular abnormalities on follow-up ocular examination. However, DTI metrics were not correlated with visual acuity or VEPS. There was large inter-subject variability within each grouping.

DISCUSSION

Mechanisms causing traumatic retinoschisis, or traumatic abnormalities of the macula, are associated with significant long-term visual pathway dysfunction. AHT associated abnormalities of the macula, and visual cortical pathways were more fully captured by VEPs than visual acuity or DTI metrics.

Including visual orienting functions into cerebral visual impairment screening: Reliability, variability, and ecological validity

BACKGROUND

Cerebral visual impairment (CVI) is a heterogeneous brain-based visual processing disorder in which basic visual orienting functions (VOF) and higher-order perception can be impaired.

AIMS

To evaluate (1) the test-retest reliability and variability of an eye tracking-based VOF paradigm, and related clinical characteristics, and (2) the relations between VOF (variability) and daily visual functioning and visuoperceptual dimensions.

METHODS AND PROCEDURES

Thirty-three children with CVI (Males=14; mean age=9 years 10 months) underwent eye tracking thrice, completed a visuoperceptual battery, and parents completed the Flemish CVI questionnaire. VOF reliability and variability of reaction time (RTF), fixation duration and accuracy were assessed with intraclass correlation coefficient (ICC), Bland-Altman plots, and coefficient of variation. Relations were analysed with linear mixed models.

OUTCOMES AND RESULTS

Highly salient visual stimuli had good RTF reliability (ICCs=0.75) and triggered less variable VOF. Intermediate and low salience stimuli had poor-to-moderate reliability and triggered more variable VOF. Younger performance age related to more VOF variability. Greater visual (dis)interest, clutter and distance viewing impairments, and a weaker visuoperceptual profile related to slower RTF.

CONCLUSIONS AND IMPLICATIONS

Highly salient stimuli reveal a child's 'optimal' visual performance, whereas intermediate and low salience stimuli uncover VOF variability, which is a key CVI hallmark to detect.

The Developmental Eye Movement Test Does Not Detect Oculomotor Problems: Evidence from Children with Nystagmus

SIGNIFICANCE

The Developmental Eye Movement (DEM) test, a test purported to assess oculomotor skills, does not detect eye movement disorder in nystagmus syndromes. The test should not be used for the clinical evaluation of oculomotor disorders.

PURPOSE

The DEM test ratio compares a horizontal number naming subtest with a vertical one to identify oculomotor problems independent of a child's visual-verbal naming skills. Here, we tested the construct validity of this method by comparing scores of children with and without pathologic nystagmus. Such a nystagmus disturbs normal fixation and saccadic behavior because of the presence of involuntary rhythmic oscillations of the eyes. Therefore, if the ratio is indeed a comprehensive measure of oculomotor problems, children with nystagmus should show an increased ratio score.

METHODS

The DEM test performances of normally sighted children (n = 94), children with ocular visual impairments (VI o ; n = 33), and children with cerebral visual impairment (n = 30) were analyzed using linear regression. Part of the children with VI o and cerebral visual impairment had either fusion maldevelopment nystagmus syndrome (n = 8) or infantile nystagmus syndrome (n = 20), whereas the others showed no pathologic nystagmus.

RESULTS

The times needed for the horizontal and vertical subtests were significantly different between children with normal vision, VI o , and cerebral visual impairment ( P < .001). However, the presence of nystagmus did not add significantly to the horizontal and vertical times ( P > .20), nor did it have an effect on the ratio ( P > .10).

CONCLUSIONS

The DEM test ratio is not sensitive to fixation and saccade abnormalities associated with nystagmus, indicating that it does not have general construct validity to detect true eye movement disorders. Although not suitable for the evaluation of oculomotor disorders, the subtests do have clinical relevance in the diagnosis of cerebral visual impairment.

The Multidisciplinary Guidelines for Diagnosis and Referral in Cerebral Visual Impairment

Introduction

Cerebral visual impairment (CVI) is an important cause of visual impairment in western countries. Perinatal hypoxic-ischemic damage is the most frequent cause of CVI but CVI can also be the result of a genetic disorder. The majority of children with CVI have cerebral palsy and/or developmental delay. Early diagnosis is crucial; however, there is a need for consensus on evidence based diagnostic tools and referral criteria. The aim of this study is to develop guidelines for diagnosis and referral in CVI according to the grade method.

Patients and Methods

We developed the guidelines according to the GRADE method 5 searches on CVI (children, developmental age ≤ 18 years) were performed in the databases Medline, Embase, and Psychinfo, each with a distinct topic.

Results

Based on evidence articles were selected on five topics: 1. Medical history and CVI-questionnaires 23 (out of 1,007). 2. Ophthalmological and orthoptic assessment 37 (out of 816). 3. Neuropsychological assessment 5 (out of 716). 4. Neuroradiological evaluation and magnetic resonance imaging (MRI) 9 (out of 723). 5. Genetic assessment 5 (out of 458).

Conclusion

In medical history taking, prematurity low birth weight and APGAR (Appearance, Pulse, Grimace, Activity, Respiration) Scores (<5) are important. Different questionnaires are advised for children under the age of 3 years, older children and for specific risk groups (extremely preterm). In ophthalmological examination, eye movements, specially saccades, accommodation, crowding, contrast sensitivity and visual fields should be evaluated. OCT can show objective signs of trans-synaptic degeneration and abnormalities in fixation and saccades can be measured with eye tracking. Screening of visual perceptive functioning is recommended and can be directive for further assessment. MRI findings in CVI in Cerebral Palsy can be structured in five groups: Brain maldevelopment, white and gray matter lesions, postnatal lesions and a normal MRI. In children with CVI and periventricular leukomalacia, brain lesion severity correlates with visual function impairment. A differentiation can be made between cortical and subcortical damage and related visual function impairment. Additional assessments (neurological or genetic) can be necessary to complete the diagnosis of CVI and/or to reveal the etiology.

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.