1. CVI Means an Under-Connected Network
According to Dr. Lotfi Merabet, the main difference in brain structure between ocular blindness and CVI is in the amount of connectivity. With ocular blindness, the brain’s connections and pathways are as strong as normal or even stronger when compared to brain imaging of sighted controls. The network that allows various parts to communicate and process effectively is fully in-tact, allowing for compensatory behaviors. For example, braille reading activates the same part of the brain as visual tasks. The brain can shift attention usually used for processing visual information to other stimuli making those senses seem enhanced. On the other hand, CVI is the opposite. It results in a thinner network of pathways that lack the stability of solid connectivity. The CVI brain is less connected, the network less able to process and communicate between its constituent parts effectively (Merabet, 2016).
2. Virtual Toy Box Adds Assessment Validity
A new tool is emerging to aid ophthalmologists, neurologists, neuro-ophthalmologists, optometrists, or clinical low vision specialists in the complex task of diagnosing CVI (How, 2021). Virtual reality offers a much more authentic assessment experience with a higher validity level than standard ophthalmologic eye exams. To accurately assess a child’s vision as well as the potential for CVI, the child must be motivated to visually attend to tasks throughout the process, which can be exhausting for them. They are not naturally motivated to look at eye charts with boring letters. Customizable virtual environments provide a much more engaging experience as well as enable demonstration of realistic visual tasks such as finding a specific shape or color in a crowded area, picking an object out of a box of several, and identifying moving targets. This assessment method also highlights the processing aspect of CVI rather than results focusing on acuity. Data shows that, among children with CVI, those have normal acuity score the same on these types of tests as those with acuity deficits (Murphy, 2021).
3. Topographic Agnosia
During an episode of hydrocephalus, the resulting white matter deterioration causes damage to the temporal lobes. This in turn causes the individual to experience topographic agnosia, or disorientation due to inability to mentally map their surroundings. Dutton concludes from this evidence that memory and prediction play a greater role in mapping locations than vision does (Lueck, 2015).
4. Perceiving Movement in Blind Spots
After studyingsoldiers with occipital cortex injuries sustained in World War I,George Riddoch discovered that movement is processed separately from other visual perceptions and can, thus, still be perceived even in scotomas (blind spots). The continued ability to recognize motion in these areas is credited either to small amounts of undamaged areas in the striate cortex or to the brain’s ability to work around the cortex altogether by using surrounding undamaged pathways instead (Martin, 2016).
5. Full Body Movement Required to Adjust Field of View
Children with acquired hemianopia (loss of half the visual field) cannot bring the missing area into view simply by turning their head, but they can if they turn their whole body along as well. For example, a child will learn to accommodate through movement. If they are trying to cross the street, they will turn their whole body to check both sides, not just move their eyes or even their head. This suggests the body movement part of the brain is connected in a fundamental way to visual scene perception. There have even been drivers who possessed such strong movement perception ability that they were unaware of their having hemianopia (Lueck, 2015).
Want to Learn More?
- Check out Dr. Lotfi Merabet’s webinar on processing differences between ocular and cerebral Visual Impairments
- Watch The Blind Woman Who Saw Rain on NPR or YouTube
- Listen to the Visual Processing webinar series by Pediatric Stroke and Brain Injury Education
Resources
How is CVI diagnosed? Perkins School for the Blind. (2021, July 27). Retrieved February 3, 2022, from https://www.perkins.org/how-is-cvi-diagnosed/
Lueck, A. H., & Dutton, G. (2015, Ch. 3). Vision and the brain: Understanding cerebral visual impairment in children. AFB Press.
Martín, M. B. C., Santos-Lozano, A., Martín-Hernández, J., López-Miguel, A., Maldonado, M., Baladrón, C., Bauer, C. M., & Merabet, L. B. (2016). Cerebral versus Ocular Visual Impairment: The impact on developmental neuroplasticity. Frontiers. Retrieved January 29, 2022, from https://www.frontiersin.org/articles/10.3389/fpsyg.2016.01958/full
Merabet, L. B. (2016, July). Comparing neuroplastic changes in ocular versus cerebral causes of visual impairment. Perkins eLearning. Retrieved February 3, 2022, from https://www.perkinselearning.org/videos/webinar/comparing-neuroplastic-changes
Murphy, G., & Merabet, L. B. (2021, March 23). 03 – visual processing, part 1 – December 11, 2020. YouTube. Retrieved February 3, 2022, from https://www.youtube.com/watch?v=oK0fGcZUFXY