There are two basic types of visual impairments: ocular and neurological (brain-based). An ocular impairment occurs when one or more parts of the eye are in some way damaged or dysfunctional such as the retina, lens, cornea, or optic nerves. Ocular impairments include retinitis pigmentosa, cataracts, and optic nerve hypoplasia or atrophy among others. In other words, the quality of the picture taken by the camera that is our eyes is poorer quality, but the brain is able to process the input normally (Lueck, 2015, Ch. 2). A brain-based visual impairment on the other hand, is the result of damage to the part of the brain which processes visual information, called the “Visual Brain” (Lueck, 2015, Ch. 1). The most currently accepted term for this type of impairment is CVI or cortical/cerebral visual impairment, though there are still debates over terminology (Perkins, 2019). Other clinical definitions of CVI specify the timeline of injury as occurring during perinatal development. Even though the quality of the image captured by the camera of the eyes may be normal, when that information reaches the brain, it is not processed as effectively. Level and type of processing issues are dependent on the severity of damage, along with which pathways or brain structures were impacted. From a functional perspective, it is critical to understand the differences between ocular and cerebral visual impairments for the simple fact that research shows instructional strategies for one group will not be effective for the other (Martin, 2016). The proposed reason is that brain restructuring due to neuroplasticity during development happens in very different ways for both groups as the brain seeks to work around issues and forge new connections (Martin, 2016).
CVI is unique in many ways, but its most significant difference, when compared to ocular impairments, is that, due to the magic of neuroplasticity, the vision of children with CVI can actually improve with time as their brains “re-route” the information to work around the damaged areas so to speak (What, 2021). Educational programming can often play a role in helping effected children maximize their visual functioning (What, 2021). With an ocular impairment, unless the damaged part of the eye can be mended or replaced, the individual will need to rely on compensatory skills and utilizing their other senses to the greatest extent possible. Two other points of divergence include visual attention and functioning. Individuals with ocular impairments have a normal ability to attend to what they choose to look at or focus on. Most with CVI however have very short fixation periods and struggle to maintain visual attention of a particular object in addition to needing frequent breaks to be able to expend the energy to focus visually. This could also be called a reduced visual attention span (Mazel, 2020). Visual functioning is also highly variable for those with CVI depending on environmental and personal factors such as amount of clutter in the room, noise, illness, and energy level (Mazel, 2020).
The two types of visual impairment do share some similarities. At the most basic level, both adversely affect functional and academic performance, requiring support and adaptation. Many children with either ocular or cerebral vision impairments experience field loss and acuity deficits, have abnormal responses to light such as photophobia or light gazing, experience fatigue from excessive visual tasks, have trouble with recognizing people who say hello walking by, and miss out on incidental, observation-based visual learning opportunities which must then be taught through direct instruction (Cortical, n.d.).
References
Cortical visual impairment: Boston Children’s hospital. Boston Childrens Hospital. (n.d.). Retrieved January 29, 2022, from https://www.childrenshospital.org/conditions-and-treatments/conditions/c/cortical-visual-impairment
Lueck, A. H., & Dutton, G. (2015). 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, January 1). 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
Mazel, Ellen. (2020, August 23). Compare ocular to cortical/cerebral visual impairments. cvi teacher. Retrieved January 29, 2022, from https://cviteacher.wordpress.com/2014/06/02/compare-ocular-to-cortical/
Perkins School for the Blind. (2019). 2019 CVI symposium. Perkins eLearning. Retrieved January 29, 2022, from https://www.perkinselearning.org/cvi/educators/symposium/2019#video
What is CVI? Perkins School for the Blind. (2021, December 16). Retrieved January 24, 2022, from https://www.perkins.org/what-is-cvi/