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

Abstract

PURPOSE.Children with cerebral visual impairment (CVI) often have abnormal visual orienting behaviors due to impaired or damaged visual cortex. Alternatively, visualcortical 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.

The Multidisciplinary Guidelines for Diagnosis and Referral in Cerebral Visual Impairment

“…Ref (Clarke et al, 1997) Low GRADE In VEP stimulation in CVI an abnormal response was found often, especially at the occipital pattern VEP (more than temporo -parietal pattern VEP). Ref (Frank et al, 1992) Moderate GRADE A subset of patients with CVI have abnormal visual orienting behaviors despite a normal VEP (visuomotor dysfunction; Kelly et al, 2021) Very low GRADE Sweep VEP nearly always deviating from normal controls, only in 16% of children with CVI a normal (straight) eye position was found. In CVI usually strabismus is found as well as motility disorders of the eyes.…”

Cortical Visual Impairments and Learning Disabilities

“…Typical clinical features of CVI may be manifest in a child, despite undetected brain signatures. Even adults with visual field loss following stroke, can show normal MRI brain imaging in 30% of cases ( Zhang et al, 2006a , b ; Kelly et al, 2021 ), as can around 12% of children with Cerebral Palsy (CP) ( Robinson et al, 2009 ; Towsley et al, 2011 ). It is therefore important to acknowledge that a report of a “normal” brain MRI in a child with neurovisual impairment does not exclude the diagnosis of CVI.…”

“…Many patterns of visual disorder can be seen, with each affected child having their own unique form of vision ( Philip and Dutton, 2014 ). Depending on the topography and extent of the pathology, the deficit may impair any aspect of visual function affecting central vision, peripheral vision (in all or part of the visual field), movement perception, gaze control, visual guidance of movement, visual attention, attentional orientation in space, visual analysis and recognition, visual memory and spatial cognition, as well as central vision, the visual fields, visual analysis, visual exploration, visual attention, or visual memory ( Kelly et al, 2021 ), in any combination, or degree. Recognition or visual memory of an object, a face or a place, the act of processing a set of stimuli or a complex scene, or difficulties directing movement or gesture under the control of vision, can be impaired in a variety of combinations.…”

“…For children who have grown up with cortical blindness that they acquired during the neonatal period but who are evaluated only at an older age, the term cortical blindness is generally inappropriate ( Watson et al, 2007 ; Werth, 2008 ). In these children, the sequelae of cortical blindness manifests as partial bilateral visual field defects such as tunnel vision (perception within a 10–20° concentric area in the central visual field) or peripheral (absence of perception in the central visual field) often accompanied by other visual cognition disorders such as simultanagnosia, visuo-motor ataxia, disorder of orientation of attention in space ( Kelly et al, 2021 ), as well as disorders of visual recognition of objects and/or faces. Children with profound CP suffering from cortical blindness who are first seen with visual difficulties years after the onset of their deficit (owing to lack of screening at birth) present a less clear picture than that of the adult in the acute phase of bilateral occipital infarction.…”

“…Cortical or cerebral visual impairment can interfere with any or all aspects of visual processing, from detection to attention, orientation, exploration, search, spatial localization or recognition of objects, scenes, places or faces ( Kelly et al, 2021 ). As a result, disorders of cerebral visual cognition such as those impairing face recognition, perception of facial expressions, gestures, movement, and the environment in general also hinder development of social and emotional interaction by impairing many of the processes necessary for communication, including acquisition of related language skills ( Pawletko et al, 2014 ).…”