Understanding cerebral/cortical visual impairment: New insights and advances in diagnosis

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Brain-based vision loss, also known as cerebral or cortical visual impairment (CVI), is one of the leading causes of blindness and visual impairment in children in the United States and other industrialized nations. However, our understanding of CVI remains limited, and there is little consensus among healthcare providers on how to define and diagnose the condition.

Researchers at Children’s Hospital Los Angeles (CHLA) are working to change that by providing clearer guidance on how CVI should be diagnosed and characterized.¹

Melinda Chang, MD, Investigator at the Vision Center at CHLA, is the lead author of a special commentary titled "Special Commentary: Cerebral/Cortical Visual Impairment Working Definition: A Report from the National Institutes of Health CVI Workshop," sponsored by the National Eye Institute (NEI) at the National Institutes of Health (NIH).

Published in the journal Ophthalmology, the report proposes a new definition of CVI as a neurodevelopmental disorder that affects visual function due to neurological damage to the brain's visual pathways and processing areas.¹

Defining CVI

Unlike the total, permanent vision loss associated with cortical blindness in adults—typically caused by strokes—children with CVI generally retain some degree of functional vision, which may improve over time. This improvement may be linked to neuroplasticity in the developing visual system. The report offers a working definition of CVI based on five key elements:

CVI as a Spectrum: CVI is not a single condition but a spectrum of visual impairments caused by brain abnormalities that affect the development of visual processing pathways.

Visual Dysfunction Beyond Ocular Conditions: Visual dysfunction in CVI exceeds what would be expected from any comorbid ocular conditions alone.

Higher-Order and Lower-Order Deficits: Visual dysfunction may manifest as difficulties with both lower-order (e.g., detecting light and motion) and higher-order visual processing (e.g., recognizing faces or objects), leading to characteristic behaviors in affected children.

Not Primarily a Language or Learning Disorder: While CVI may co-occur with other neurodevelopmental disorders, it is not primarily a disorder of language, learning, or social communication.

Neurological Damage May Be Undiagnosed: The underlying neurological damage in the brain may go unrecognized or undiagnosed, sometimes until later in a child's development.

The importance of early detection

“Early detection of CVI is crucial to facilitate early intervention,” says Dr. Chang. “Studies of children with ocular causes of visual impairment have shown consistent associations between visual impairment and challenges in learning, social relationships, and overall quality of life. Emerging research on children with brain-based vision impairment shows similar patterns.”

To address this, the NIH is developing a CVI registry to gather demographic and clinical data. Future research will focus on understanding the neurophysiological basis of neuroplasticity in children with CVI, developing standardized methods of visual assessment, and evaluating the effectiveness of proposed treatments.

Guidance for clinicians: Identifying and diagnosing CVI

In a companion paper, “Diagnosis and Care of Children with Cerebral/Cortical Visual Impairment,” published in Pediatrics, Chang, Larry Yin, MD, MSPH, Chief of General Pediatrics at CHLA, and Sharon Lehman, MD, FAAP, a pediatric ophthalmologist at Nemours Children’s Health, discuss how CVI is diagnosed and managed.

Routine vision screenings may not detect CVI, so it’s important for clinicians to consider the child’s medical history and behavioral characteristics. Children at risk for CVI may have experienced early neurological injury, such as preterm birth, hypoxic-ischemic encephalopathy, or brain trauma, leading to conditions like epilepsy, cerebral palsy, or intellectual disabilities. For these children, a referral for a pediatric ophthalmologic evaluation is essential.

Behavioral characteristics of CVI

The authors outline several behavioral signs of CVI, which result from dysfunction in the brain's visual processing pathways. These may include:

• Day-to-day Variability: Children with CVI often experience significant variation in their visual abilities from day to day.
• Delayed Responses or Light Gazing: Children may take longer to respond to visual stimuli, or they may show a preference for gazing at lights or demonstrate an aversion to light.
• Motion Dependency: Some children require motion to respond to visual stimuli.
• Difficulty with Object Recognition: Children may have trouble identifying objects in complex visual environments, such as finding a toy in a toy box or an item of clothing in a pile.
• Difficulty Recognizing Faces or Objects: Impaired recognition of familiar faces or objects is a common feature of CVI.

Advancing diagnostic tools and techniques

Although standard diagnostic tools like structural magnetic resonance imaging (MRI), electrophysiologic tests, and electroretinography cannot consistently diagnose CVI, emerging technologies show promise. Functional MRI (fMRI) and diffusion tensor imaging (DTI) may help identify brain abnormalities associated with CVI. Additionally, researchers are investigating improved methods for assessing visual function in children with CVI, including:

• Preferential Looking Tests: Assessing a child's preference for looking at visual stimuli.
• Sweep Visual Evoked Potentials (VEPs): Measuring the brain’s response to visual stimuli.
• Functional Vision Assessments: Evaluating how well a child uses their vision in daily life.
• Neuropsychological Testing: Understanding visual perception abilities.
• Eye Tracking: Monitoring how a child’s eyes track and focus on visual stimuli.

Conclusion

Cerebral/cortical visual impairment (CVI) is a complex and often under-recognized condition that can significantly affect a child's development and quality of life. By refining the definition of CVI, improving diagnostic tools, and promoting early intervention, researchers and clinicians aim to provide better care and outcomes for children affected by this brain-based visual impairment. As research continues to evolve, these advancements will lead to more effective treatments and a deeper understanding of how the brain processes vision.

“Learning the characteristics and risk factors can enable physicians to identify children with CVI and coordinate effective evaluation, diagnosis, and referrals for vision services,” Chang concluded. “While early intervention is ideal, the optimal timing and type of intervention have not been established. Through our work, we hope to determine the best treatments for these children in the future.”

Reference

1. Cerebral/Cortical Visual Impairment Working Definition Chang, Melinda Y.Borchert, Mark et al. Ophthalmology, Volume 131, Issue 12, 1359 – 1365. Accessed November 22, 2024.