Cortical or Cerebral Visual Impairment in Children: A Brief Overview

Abstract

The brain is intricate in its design and function. Neuroscientists and neuropsychologists are revamping concepts and principles that are related to brain function and vision as more information is obtained and understood. The changes that are emerging from brain research are altering our understanding of cortical or cerebral visual impairment (CVI) in children. In addition, injury to the brain can result in functional manifestations that are complex and multifaceted. These functional manifestations are related to the extent, location, and time of onset of the brain lesions, but the precise effects of these injuries cannot be readily and fully predicted in children from the brain lesions themselves. For example, we have no idea of the ways in which areas of the brain that are intact in young children who have brain damage assume the functions of damaged areas owing to the plasticity of the brain. Thus, an understanding of recovery mechanisms for CVI in children and of the effects of intervention is in its infancy. As a result, our understanding of the nature of CVI in children must be open and flexible as we incorporate and learn to apply an ever-evolving knowledge base. We must understand the issues surrounding CVI, embrace their complexity and lack of closure, and determine directions for the effective diagnosis and treatment of children with CVI from medical and educational perspectives. WHAT IS CVI? The story of CVI that is due to brain injury began in the late 19th century with the emergence of the concept that vision was associated with brain function, most notably with the operations of the occipital cortex. As Hoyt (2003) noted, permanent field loss came to be associated with damage to the visual cortex through work conducted by neurologist Gordon Holmes with veterans who were injured during World War I. There were puzzling discrepancies even at that time, since Gordon Riddoch, of the Royal Army Medical Corps, found that some World War I veterans with injuries to the occipital cortex could perceive motion in their visual field. This ability to detect motion as well as other visual events in the nonseeing visual field has been called blindsight. Blindsight is awareness of moving targets, lights, and colors in the blind area, and this awareness can be either conscious or subconscious (called statokinetic dissociation or the Riddoch phenomenon in adults). It is difficult to determine in children because of their young age and co-occurring impairments (Boyle, Jones, Hamilton, Spowart, & Dutton, 2005). Before the 1980s, the absence of sight that is due to bilateral damage to the occipital cortex was called cortical blindness. This term was derived from studies of adults, but was applied to children as well. Cortical blindness, however, was considered to be rare in children, according to Hoyt (2003). Many children with visual impairments that were due to brain damage recovered their visual function and were not totally blind (Hoyt, 2003; Whiting et al., 1985). In the late 1980s, the term cortical blindness gave way to the term cortical visual impairment or CVI. At that time, the generally accepted definition of CVI was damage to the visual system between the lateral geniculate nucleus and the visual cortex. A reduction in visual acuity was the way that CVI was identified (Jan & Groenwald, 1993). Basically, the eyes appeared to be normal, yet there was diminished visual acuity because of a diagnosed brain damage. Later, it became more common in the literature to find that CVI often co-occurred with other visual conditions, as was mentioned earlier (Good, Jan, Burden, Skoczenski, & Candy, 2001). Visual behaviors and perception related to damage to other areas in the brain were not considered cortical, and thus children with damage outside the cortex were not included under the CVI umbrella. As researchers learned more about brain damage and visual impairment, they found that periventricular leukomalacia (PVL), damage to the white matter surrounding the ventricles in the brain, was a common cause of visual impairment in children who were born preterm (Jacobson, Lundin, Flodmark, & Ellstrom, 1998). …