The following information on CVI, its definition, description of the ten characteristics, and guiding principles of cortical visual impairment are the work of Christine Roman-Lantzy and come directly from her book, with permission, Cortical Visual Impairment, An Approach to Assessment and Intervention (AFB Press, 2007).
Cortical visual impairment (CVI) is the leading cause of visual impairment in children in the US and developed countries, yet most people have not heard of it. CVI is a brain based visual impairment, it is a problem with the brain, not the eye. “The child sees what we see, but they can’t interpret it.” The functional vision of children with CVI is expected to improve, especially with carefully planned interventions based on a child’s CVI Range score (Roman-Lantzy). Early diagnosis and interventions are critical for maximum improvement (see, In infants with CVI, below).
When Jasper was diagnosed with “cortical blindness” at one week old, the neurologist said, Because his impairment involves the brain, and not the eye, there is nothing we can do. Instead the neurologist should have said, Because his impairment involves the brain, and not the eye, there is so much we can do. This should be the message to all parents whose child receives a diagnosis of cortical visual impairment. In this way and others, CVI is fundamentally different from ocular impairments, which are usually progressive.
The most common causes of CVI in children are “perinatal hypoxia [hypoxic-ischemic encephalopathy, HIE, sometimes called infant stroke], prematurity and hydrocephalus. Other etiologies in children and adults include: traumatic brain injury; stroke; congenital anomalies; central nervous system infections; neonatal hypoglycemia; and seizures.” Children who present with these conditions should be screened for CVI.
What is cortical visual impairment?
CVI differs from ocular forms of visual impairment in that the interference in visual function exists not in the structures of the eye or optic nerve, but in the visual processing centers and visual pathways of the brain (Jan & Groenveld, 1993).
1. CVI is best identified and diagnosed by the following: a normal eye exam, or an eye exam that reveals an eye condition that does not explain the profound lack of functional vision; a medical history that includes neurological problems; the presence of unique visual and behavioral characteristics.
2. We call these unique visual and behavioral characteristics the ten characteristics of CVI:
Attention to light
Attraction to movement
Preferred visual field
Difficulties with visual and environmental complexity
Difficulty with distance viewing
Absent or atypical visual reflexes
Difficulty with visual novelty
Absence of visually guided reach
3. In infants with CVI: Visual function improves or declines but rarely remains static. Vision can be rehabilitated with permanent increased function during the critical window of visual plasticity in the period of infancy.
4. In older students with CVI: It is unknown when plasticity regarding the development of vision ends; therefore, progress in visual function should be expected, although the rate may be slower when the child is beyond the critical period of visual plasticity in infancy. Adaptations must be designed on the basis of assessed needs. Interventions should be integrated into daily routines.
5. CVI may coexist with ocular forms of visual impairment.
6. Functional vision assessment for students with CVI has a specialized protocol (CVI Range).
7. Interventions for children with CVI must emerge from assessed needs.
8. Environments for children with CVI must be adapted. Adaptations must consider visual complexity, auditory complexity, and be embedded as part of the daily routine rather than a stand-alone “treatment.”