What does the acronym “CVI” represent? At one time it stood for Cortical Visual Impairment, but it is now more widely referred to as Cerebral Visual Impairment. It’s about time that change occurred.
A rose by another name? Not at all. In fact the transition to the more diffuse notion of cerebral rather than cortical addresses an age old question I had. How could a child with CVI have a normal pattern VEP response? The answer, by definition, had to be that the impairment resided in areas of visual cortex other than V1 – which reminds us how much there is to vision in the visual pathways beyond visual acuity.
A book that was co-authored last year by Professors Zihl and Dutton captures the essence of CVI in its subtitle of visuoperceptive and visuocognitive disorders.
Here are some nice sound bites from the book:
- To a major extent, vision is a skills that depends on learning and use, just as other skills such as walking or talking.
- The field of attention in young children is not fully developed, and they may therefore ignore peripheral stimuli particularly when they appear simultaneously in both hemi-fields.
- Reading requires various functional prerequisites including visual, oculomotor, and cognitive functions that facilitate reception, processing, and understanding of spatially distributed visual-verbal information.
- Sensitivity to word visibility increases between 7 and 12 years of age, which is associated with developmental changes in activation in left occipital-parietal regions.
- Vergence and accommodation are best understood as calibration and recalibration processes to various fixation distances, which are controlled by neural structures in the brainstem, cerebellum and cerebral cortex and in addition are influenced by attention and the intention of visual information processing.
- It is possible to have CVI with near normal visual acuity, and crowding can occur due to a variety of visual interferences. Visual crowding due to CVI can impair reading. For children who are hyperopic or those with impaired accommodation, positive lenses both magnify text and allow it to be read closer to the eyes, bringing about additional magnification due to proximity. This can in turn reduce crowding of text on the printed page, which can enhance access to the printed word. Correction of only one or two diopters of hyperopia can benefit some children with CVI.