Most people don't understand how primitive our understanding of vision is. Medical science does pretty well with refractive errors of the eye, but it often drops the ball when it comes to recognizing brain-based disorders of visual perception or processing.
The problem is, we don't really know what other people see - and because it is subjective, it is also hard to study "higher order vision" in animal models. Too often we see children with brain-based visual processing problems who have been unrecognized or misdiagnosed for years because no one knew that an eye chart was a poor way to identify problems with brain-based or central visual impairment.
In studies of young adults with a perinatal injury to the corpus callosum, researchers (see right) found that these individuals had to work much harder to visually match figures than age-matched or normal callosum controls. Interestingly, this study also showed extra "work" that these test subjects needed to perform when listening and matching sounds. No wonder that for many children, it's difficult to both listen and look at the same time.
For an excellent recent paper detailing some of the practical (school and home life) challenges facing children with brain-based visual problems check out Gordon Dutton's recent review here.
- Clarity of vision often varied (affecting reading) and worsened with fatigue
- Children often preferred pictures with clear color boundaries
- Increasing the font (and the spacing between letters) often improved reading ability
- Teachers had to be instructed that children with visual problems might appear to look past them because they could see better out of the sides of their vision.
- For some kids, reading vertically was easier.
- Some children struggle with visual movement and this may impact the playground as well as the TV - a preference for stationary subjects (for instance prefer watching the news instead of cartoons)
- Errors with direct copying improved if the children verbalized what they saw as they copied
- Visual crowding and complexity were a big obstacle - so reducing the visual distractions or complexity of school materials would help. Interestingly, visual crowding also contributed to food issues and social difficulties (hard to look and listen at the same time).
- Problems and tips about visual recognition, spatial orientation, and social and emotional issues are also discussed.
Children with visual processing problems often have a history of premature birth, birth stress, or a condition such as dyslexia. Because of the importance of visual cues in normal human interactions, many children with brain-based visual impairments are misdiagnosed as having Asperger Syndrome, PDD-NOS, or an attention deficit disorder.
If you have a child you suspect may have central visual impairment or CVI, you may need to look carefully for professionals with specific expertise in this area; for special glasses (prisms) or therapeutic intervention, often a fellow of the COVD will also be needed.
Perinatal Corpus Callosum Damage in Young Adults pdf
Recent advances in central visual impairment pdf
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