Special Commentary: Cerebral/Cortical Visual Impairment Working Definition: A Report from the National Institutes of Health CVI Workshop
Authors:
Melinda Y. Chang, MD; Lotfi B. Merabet, OD, PhD; CVI Working Group
Special thanks to Anis Hilal, MD, for contributions to this summary.
Main Research Question: Defining Cerebral/Cortical Visual Impairment
How can Cerebral/Cortical Visual Impairment (CVI) be effectively defined, and what are the implications of a standardized definition for diagnosis, research, and clinical care?
Key Findings/Results:
Cerebral/Cortical Visual Impairment (CVI), a leading cause of pediatric visual impairment, is a brain-based disorder resulting from neurologic abnormalities that affect visual processing pathways in the brain. The newly proposed working definition by the NIH CVI Working Group identifies five key elements critical to understanding and diagnosing this complex condition:
1 Broad Spectrum of Impairments: CVI encompasses a spectrum of visual deficits arising from neurological abnormalities. These impairments impact both visual function (which is assessed in clinical situations using metrics such as visual acuity) and functional vision (the ability to use vision in everyday tasks).
2 Beyond Ocular Conditions: CVI is distinct from visual dysfunctions caused by ocular pathologies, such as optic nerve hypoplasia or retinopathy of prematurity. In CVI, the level of visual impairment cannot be solely attributed to these comorbidities.
3 Varied Deficits: The disorder may manifest as lower-order visual deficits (e.g., reduced acuity, contrast sensitivity, or visual field issues) or higher-order deficits (e.g., difficulties with motion perception, object recognition, or visuospatial tasks).
4 Comorbidities: CVI may coexist with neurodevelopmental disorders such as autism or dyslexia, but it is distinct in etiology and manifestation. Importantly, CVI is not primarily a disorder of social communication or learning, although these aspects may overlap.
5 Delayed Recognition: Many cases are diagnosed later in childhood or even in adulthood due to overlapping symptoms with other conditions or compensatory mechanisms adopted by individuals with CVI.
Methodology Used:
The National Institutes of Health (NIH) held a CVI Workshop in November 2023 to unify the field’s understanding of CVI. Experts across ophthalmology, optometry, and neurology collaborated to develop this working definition, emphasizing a literature review, clinical observations, and expert consensus. The effort also considered gaps in existing definitions and diagnostic practices.
Significance of the Study:
The proposed definition clarifies areas marked by inconsistent terminology and diagnostic criteria. This clarity is crucial for clinical care, early intervention, and research. It emphasizes the need for interdisciplinary approaches and highlights areas requiring further research, including understanding neuroplasticity in the visual system, identifying early biomarkers for diagnosis, and developing targeted therapies.
Main Conclusions: A Working Definition for Cerebral/Cortical Visual Impairment
CVI is a neurodevelopmental condition marked by deficits in visual function and functional vision, caused by neurologic damage to visual pathways and processing areas. Unlike traditional ocular conditions, CVI involves complex brain-based impairments that require unique diagnostic and therapeutic approaches. Early identification and intervention are emphasized as critical for improving developmental outcomes.
Detailed Breakdown:
CVI as a Spectrum of Visual Impairments
CVI encompasses a range of visual deficits due to neurologic injury, affecting visual processing pathways in the brain. Visual dysfunction in CVI can significantly impair an individual’s ability to perform tasks requiring vision, but the deficits may not always be captured by standard clinical assessments, such as visual acuity tests. This distinction between visual function (clinical measurement) and functional vision (real-world performance) is pivotal in understanding CVI’s impact on daily life. Neurological causes include conditions such as hypoxic-ischemic encephalopathy, periventricular leukomalacia, trauma, and genetic disorders. Advances in neuroimaging techniques, including diffusion-based imaging and functional connectivity studies, reveal underlying structural and functional changes even when conventional imaging appears normal.
Visual Dysfunction Beyond Ocular Conditions
CVI may coexist with ocular conditions like optic nerve atrophy or retinopathy of prematurity. The working group emphasized that CVI should only be diagnosed when visual dysfunction exceeds what is expected from ocular conditions alone. Patients may also have oculomotor conditions such as strabismus, nystagmus, or oculomotor difficulties, but these alone do not constitute CVI.
Lower-Order and Higher-Order Visual Deficits
CVI can manifest through:
- Lower-order deficits: Reduced visual acuity, contrast sensitivity, and visual field limitations, among others. These are often detected in early childhood and may initially overshadow higher-order deficits.
- Higher-order deficits: Challenges with complex visual processing, including difficulties in recognizing faces, objects, or spatial relationships. These deficits are linked to dysfunctions in the visual association areas and dorsal/ventral stream pathways.
Behavioral traits, such as light gazing, preference for brightly colored objects, or difficulties with visual search in cluttered environments, may provide early clues. Standardized tools, including neuropsychological assessments, semistructured histories, and clinical examination, functional vision assessment, and neuroimaging and genetic testing when appropriate are critical in diagnosing these impairments.
Comorbid Neurodevelopmental Disorders
CVI frequently co-occurs with conditions such as cerebral palsy, autism, and dyslexia. This overlap complicates diagnosis but also underscores the importance of multidisciplinary care. Unlike autism, which involves deficits in social communication, or dyslexia, marked by challenges in reading and spelling, CVI’s primary feature is impaired visual processing. However, these conditions may share underlying neurodevelopmental causes, requiring careful evaluation to disentangle overlapping symptoms.
Delayed Diagnosis and Lifelong Support
Diagnosis may occur late due to the subtlety of symptoms or the absence of visible brain lesions on routine imaging. The group introduced the term “CVI suspect” for individuals presenting with signs of CVI but requiring further assessment. Pediatricians play a vital role in early screening, especially for at-risk populations with histories of neonatal brain injury. Evidence suggests a critical period for visual system development within the first decade of life, emphasizing the importance of timely interventions.
Future Directions and Implications for Clinical Practice
Future Directions:
The NIH aims to establish a CVI registry to collect longitudinal data, aiding research on neuroplasticity, diagnostic biomarkers, and the efficacy of interventions. Key research priorities include:
- Understanding how neuroplasticity shapes visual function and prognosis in CVI.
- Standardizing diagnostic tools, particularly for higher-order deficits.
- Evaluating how functional impairments evolve over the lifespan.
- Developing evidence-based treatments tailored to individual needs.
Implications for Clinical Practice:
The working definition highlights the need for:
- Multidisciplinary diagnostic approaches, involving ophthalmologists, optometrists, neurologists, educators, therapists, and other allied health personnel.
- Early interventions, including environmental modifications and rehabilitation strategies.
- Lifespan care models that transition seamlessly from pediatric to adult services.
Conclusion:
The NIH CVI Working Group’s definition of CVI offers a foundational framework for improving diagnosis, research, and patient outcomes. It emphasizes the complexity of brain-based visual impairments and the need for early, tailored interventions. By standardizing terminology and diagnostic practices, this effort aims to enhance understanding of CVI and its impact, ultimately fostering better care across the lifespan.
Chang MY, Merabet LB; CVI Working Group. Special Commentary: Cerebral/Cortical Visual Impairment Working Definition: A Report from the National Institutes of Health CVI Workshop. Ophthalmology. 2024 Dec;131(12):1359-1365. doi: 10.1016/j.ophtha.2024.09.017. PMID: 39572128; PMCID: PMC11588029.