Experts convened by the National Institutes of Health (NIH) have identified five elements of a brain condition that has become a leading cause of visual impairment since childhood in the United States and other industrialized nations. Known as cerebral (or cortical) visual impairment, some estimates suggest that at least 3% of primary school children have CVI-related visual problems, which vary but can include difficulty visually searching for an object or person or understanding a scene that involve complex movements. Their report, based on evidence and expert opinion, was published today in Ophthalmology.
“Lack of awareness about CVI is a major factor leading to it being misdiagnosed or undiagnosed, which can mean years of frustration for children and parents who are unaware of an underlying vision problem and receive no help to fix it.” “said the report. -author, Lotfi B. Merabet, OD, Ph.D., associate professor of ophthalmology, Massachusetts Eye and Ear and Harvard Medical School, Boston.
“Clarifying the factors for suspecting CVI should help raise awareness and help eye care providers identify children for further evaluation, so that they can benefit from rehabilitation and adaptation strategies as soon as possible,” said the Report co-author Melinda Y. Chang, MD, Asst. professor of clinical ophthalmology at the University of Southern California, Los Angeles.
Experts report that the five elements of the CVI are:
- Brain involvement: CVI encompasses a spectrum of visual impairments that involve an underlying brain abnormality that affects the development of the visual pathways (the neural connections in the brain that process vision). In all people with CVI, these visual pathway abnormalities result in some degree of functional visual impairment, which interferes with how a person can use their vision for everyday activities.
- Visual dysfunction greater than expected based on eye exam: People with CVI may have a coexisting eye problem. When visual dysfunction is primarily based on a visual processing problem in the brain and cannot be explained by the eye problem, CVI should be diagnosed.
- Types of visual deficits: CVI-related visual dysfunction can manifest as lower- 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 extent of vision). Higher-order deficits may include difficulty with face and object recognition, decreased ability to visually search for something or someone, difficulty with spatial orientation or the perception of complex movements, and seeing more than one object at a time.
- Distinguish overlapping neurological disorders: Although CVI can coexist with other neurodevelopmental disorders, it is not primarily a disorder of language, learning, or social communication. Cerebral palsy is common among people with CVI, and autism and dyslexia may have overlapping manifestations with those of CVI. As a result, CVI is prone to misdiagnosis and underdiagnosis in children with other co-occurring neurodevelopmental disorders.
- CVI is easily overlooked: The underlying neurological abnormality of a child’s developing brain may go unnoticed or undiagnosed until later in life, when the individual is able to recognize and express his or her functional visual deficits. Screening for CVI should be considered in people who are at high risk for having suffered a neurological injury, such as babies born prematurely with periventricular leukomalacia, an abnormality of the ventricles of the brain that is detected on imaging. However, current imaging technology is often not sufficient to diagnose CVI.
The CVI definition report is based on a workshop organized 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).