Experts convened by the National Institutes of Health (NIH) have identified five elements of a brain-based condition that has emerged as a leading cause of vision impairment starting in childhood in the United States and other industrialized nations. Known as cerebral (or cortical) visual impairment (CVI), some estimates suggest that at least 3% of primary school children exhibit CVI-related visual problems , which vary, but may include difficulty visually searching for an object or person or understanding a scene involving complex motion. Their report, based on evidence and expert opinion, was published today in Ophthalmology.
"Lack of awareness about CVI is a large factor leading to it to be misdiagnosed or undiagnosed, which can mean years of frustration for children and parents who are unaware of an underlying vision issue and don't receive help for it," said report co-author, Lotfi B. Merabet, O.D., Ph.D., associate professor of ophthalmology, Massachusetts Eye and Ear and Harvard Medical School, Boston.
"Clarifying the factors for suspecting CVI should help build awareness and help eye care providers identify children for further assessment so they can benefit from rehabilitation and accommodation strategies as early as possible," said report co-author, Melinda Y. Chang, M.D., assistant professor of clinical ophthalmology at the University of Southern California, Los Angeles.
Experts report that the five elements of CVI are:
- Brain Involvement: CVI encompasses a spectrum of visual impairments that involve an underlying brain abnormality affecting the development of visual pathways (the brain's neural connections that process vision). In all people with CVI, these visual pathway abnormalities result in some degree of functional vision impairment, which interferes with how a person is able to use their vision for everyday activities.
- Visual dysfunction greater than expected based on eye exam: People with CVI may have a co-existing problem with their eyes. When the visual dysfunction is based primarily on a visual processing problem in the brain and cannot be explained by the ocular problem, CVI should be diagnosed.
- Types of visual deficits: CVI-related visual dysfunction can manifest as lower-order and higher-order visual deficits. Examples of lower-order deficits include impaired visual acuity (not seeing an eye chart clearly), reduced contrast sensitivity and reduced visual field (the scope of one's vision). Higher-order deficits can include difficulty with face and object recognition, lessened ability to visually search for something or someone, difficulty with spatial orientation or complex motion perception, and seeing more than one object at a time.
- Distinguishing overlapping neurological disorders: While CVI can co-occur with other neurodevelopmental disorders, it is not primarily a disorder of language, learning, or social communication. Cerebral palsy is common among individuals with CVI, and autism and dyslexia can have overlapping manifestations with CVI. As a result, CVI is prone to misdiagnosis and underdiagnosis in children with other concurrent neurodevelopmental disorders.
- CVI is easily missed: The underlying neurological abnormality of a child's developing brain may go unrecognized or undiagnosed until later in life when the individual is able to recognize and express their functional vision deficits. Screening for CVI should be considered in individuals who are at high risk of having had a neurological injury, such as infants born prematurely with periventricular leukomalacia, an abnormality of the brain's ventricles found on imaging. However, current imaging technology is often not sufficient to diagnose CVI.
"Significant work remains to be done to optimize diagnostic approaches and multidisciplinary rehabilitation strategies to improve quality of life for people with CVI, which is why it is a priority in our strategic plan," said Michael F. Chiang, M.D., director of NIH's National Eye Institute (NEI).
To move research forward, NEI is overseeing the development of a registry to amass data from people with CVI. The database resource will be made available for researchers to study the spectrum of CVI's signs and symptoms and to define best diagnostic and rehabilitative practices. To learn more, visit the NIH CVI Registry webpage .
The CVI definition report is based on a workshop hosted by the NEI in partnership with the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) and the National Institute of Neurological Disorders and Stroke (NINDS).
A complementary report from the American Academy of Pediatrics to help pediatricians recognize CVI was published today in Pediatrics.
