An evolving explanatory framework for understanding the complex profile of cerebral visual impairment

Cerebral visual impairment (CVI) is an umbrella term for a heterogeneous, brain-based visual disorder. We propose that a network or “systems” neuroscience perspective may be helpful to further our understanding of the complex visual dysfunctions and clinical profile that characterizes CVI. In the same way that a more holistic approach is needed to assess a child’s needs, there should also be a more holistic whole brain approach to understanding the complex behavioral profile of CVI. The past decades have seen a dramatic shift in the etiological profile of children with visual impairment and blindness. CVI now represents the most common cause of pediatric visual impairment and blindness in developing countries (Solebo et al., 2017). Accordingly, the shift from primarily ocular to brain-based causes of visual impairment has important clinical, habilitative, and educational consequences for the well-being of these individuals. A recent meta-analysis has led to a proposed definition of CVI as “verifiable visual dysfunction that cannot be attributed to disorders of the anterior visual pathways or any potentially co-occurring ocular impairment” (Sakki et al., 2017). As an umbrella term, this definition emphasizes the role of neurological and/or developmental injury as the primary cause of visual dysfunctions in CVI. However, given the broad and heterogeneous clinical profile that typically accompanies this population, we now ask ourselves, “what exactly does this definition mean from a functional perspective?” For some individuals, impaired visual functions include reduced visual acuity, visual field, and contrast sensitivity which can be captured in the clinical setting. For others, higher order perceptual impairments represent their main visual difficulties, despite having visual acuities within normal/near-normal ranges. There are also individuals with CVI who present with severe comorbidities (such as cerebral palsy, autism spectrum disorder, or a history of developmental and cognitive delays) that can make visual functions more challenging to assess and can mask higher order perceptual impairments. This poses challenges with respect to disentangling the association between these comorbidities from underlying visual perceptual deficits (Hyvärinen, 2019). The causes of brain injury and/or maldevelopment in CVI (e.g., hypoxic/ischemic damage, trauma, and genetic/metabolic disorders) are also very heterogeneous in terms of type, severity, and extent. In some cases, CVI can present without evidence of clear neurological injury (observable by standard magnetic resonance imaging [MRI]). The broad etiology of CVI highlights the importance of understanding the contribution of central brain structures at all levels (including subcortical, cortical, and white matter pathways) as well as accounting for potential co-occurring impairments due to pathology at the level of the eye. An early description by Good and Rutherford (1994) proposed that individuals with CVI had vision akin to viewing through a “Swiss cheese” visual field to describe areas of higher and lower acuity and to account for often-reported fluctuations in vision. Poor attention could make it harder for a child to orient to a visual target within an area of preserved visual field (Good & Rutherford, 1994). Based on the classic two-stream (i.e., dorsal and ventral) model of visual processing, 1163652 JVI0010.1177/02646196231163652British Journal of Visual ImpairmentEditorial editorial2023