Statement on Cortical Visual Impairment

Abstract

In August 2008, the American Printing House for the Blind (APH) brought together an advisory group to provide guidance and clarity on a range of issues related to cortical visual impairment (CVI) as those issues relate to the development of products. The internationally drawn CVI Advisory Group, with members suggested by APH ex officio trustees and consultants, represents a continuing effort by APH to serve the growing group of students with CVI who are registered for Federal Quota funds. Previous activities conducted by APH on behalf of these students have included improving the Federal Quota registration process by better defining eligibility criteria; hosting a CVI Synergy meeting in Louisville, Kentucky; identifying existing APH products that serve the unique needs of this population; developing and manufacturing new products for students with CVI; creating a CVI web site; and providing information on APH products that are related to students with CVI through workshops of the APH National Instructional Partnership. DEFINITION OF CVI: A WORKING DEFINITION FOR EDUCATIONAL SERVICES CVI is defined as impaired vision that is due to bilateral dysfunction of the optic radiations or visual cortex or both. It can coexist with ocular and ocular motor disorders and can be the result of perinatal brain dysfunction or be caused by trauma. Approximately 30%-40% of children with visual impairments have CVI (see Figure 1, which can be viewed in an area dedicated to CVI on the American Foundation for the Blind's web site at ). One concern of professionals in the field of education of students with visual impairments is to establish a standard definition of CVI. Accordingly, the purpose of this article is to clarify the differences between children who qualify for services from vision educators and those who have visual processing difficulties that are not considered visual impairment. Our perspective is that all children who have CVI should be classified as visually impaired and receive the necessary services, regardless of the severity of the degree of CVI or additional disabilities. A child with CVI is distinguished from a child with learning disabilities or developmental disabilities by the following criteria: (1) an eye examination that cannot fully explain the child's use of vision; (2) a history or presence of neurological problems, even when the child's brain-imaging studies may appear normal (Dutton, 2008); and (3) the presence of the behavioral or visual responses that are collectively associated with CVI. In most North American jurisdictions, low vision is defined as a reduction in visual acuity no better than 20/70 (6/21) but better than 20/200 (6/60) in the better eye with the best correction. Legal blindness is defined as visual acuity no better than 20/200 (6/60) in the better eye with the best correction. Legal blindness is also defined as a central visual field that is no greater than 20 degrees. Using this framework, CVI should be defined, albeit arbitrarily, by a reduction in visual acuity, in the visual fields, or in a child's ability to see compared to other children of the same age. Unfortunately, traditional methods of precisely determining acuity or visual field function in children with CVI are problematic. Because children with CVI frequently have additional disabilities, it is often difficult to measure visual acuity. When it is possible to do so, standard visual acuity testing should be performed. Electrophysiological measures, such as visual evoked potential acuities, may also be used. When warranted, visual acuities should be measured using forced-choice preferential looking acuities or estimating visual function through the identification of sized objects at specific distances. Dutton (2008) and others have proposed a theoretical construct for classifying higher-level visual processing. This framework considers the effects of damage to the dorsal and ventral streams of the brain to explain visual dysfunction. …