What is CVI?

What is CVI?
Cerebral Visual Impairment (CVI) is defined as bilateral visual impairment caused by damage to the posterior visual pathway, visual cortex or both. (Watson, et al, 2007; Malkowicz, et al, 2006; Hoyt, 2003; Jan & Groenveld 1993) (Fig. 1) There are many causes of CVI; the most common is Hypoxic-ischemic Encephalopathy (HIE). Other causes of CVI include infections, central nervous system malformations, neurological disorders, epilepsy, metabolic and neurodegenerative disorders, cerebral infarct or trauma. (Groenveld, et al, 1990; Jan & Groenveld, 1993; Morse, et al, 1990; Ek, et al, 2003; Malkowicz, et al, 2006)




Prevalence
CVI is clearly the most common cause of visual impairment in young children in developed countries. (Dutton et al, 1996; Hoyt, 2003; Jugnoo & Noriko, 2003; Rosenberg et al, 1996) In 1994 Chile, 2.1% children are diagnosed as CVI. In Huo’s 1999 study, 2.4% of 7,200 patients are examined as CVI in United Stated. In Hatton’s study published in eight years later, CVI dramatically increase to 24% of 1943 patients (quotated in National registry) examined in United Stated. In Northern Ireland, Belfast’s study revealed 45% of 76 patients are found to be CVI in the community. One of the reasons explaining the dramatic increase is the improvement in brain imaging techniques like Magnetic Resonance Imaging, MRI; Computed Tomography, CT Scan; Visual evoked potential, VEP & Electroencephalography (EEG), (Alexander, 1990; Good, et al, 2001; Widdig, et al, 2003; Watson, et al, 2007; Ro & Rafal, 2006) Second reason is the increased researches investigating this area were published in recent decade. These provoke the recognition of Medical officers in diagnosing CVI. Third reason is thanks to the advanced medical technologies like Hypothermia (Zanelli et al, 2008) in treating children with perinatal Hypoxic-ischemic Encephalopathy, HIE. The mortality rate was 16% in Canada from 1996 to 1997 while it was 10% in US in 2005 to 2006.
References:
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Dutton, G.N., Saaed, A., Fahad, B., Fraser, R., Madaid, G., Mcdade, J., Mackintosh, A., Rane, T., & Spowart, K. (2004). Association of binocular lower visual field impairment, impaired simultaneous perception, disordered visually guided motion and inaccurate saccades in children with cerebral visual dysfunction – A retrospective observational study. Eye, 18, 27-34.
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Zanelli, S. A., Naylor, M., Dobbins, N. (2008) Implementation of a “hypothermia for HIE” program: 2-year experience in a single NICU. Journal of Perinatology, 2(28), 171–175.