Quantifying Visual Functions in Children with Cerebral Visual Impairment (CVI)

Patients with cerebral visual impairment (CVI, formerly cortical visual impairment) have vision loss resulting from an insult to the brain rather than to ocular structures. These children and their parents must attempt to understand their unique form of vision loss which often develops in an unpredictable fashion, and can go undiagnosed by an eye care provider. Furthermore, it can be difficult to advocate for children with CVI as many individuals and professionals who may interact with the child are unfamiliar with the condition. Although there is much interest in CVI as it is currently the leading cause of vision loss in children in the developed world, many aspects of vision loss in CVI are not well understood nor quantified./nThe first two studies were aimed at understanding the effect of contour interaction on visual acuity in children with CVI. The first study shows a negative effect of contour interaction, the deleterious effect of identifying an object in the presence of other objects, on visual acuity in children with CVI as well as normally sighted children. This difference is more significant for children with CVI – and for this group, the greater the reduction of visual acuity, the greater the reduction in acuity with increased contour interaction. The second study shows that the critical spacing of this effect is about twice as large in children with CVI as compared to normally sighted children. The fifth study compared this effect in children with CVI to children with retinal disease. Surprisingly, there was minimal difference in the contour interaction effect between the two groups when looking at the average difference between measures. However, the slope of the trend was quite different for children with CVI versus children with retinal disease, implying that the underlying mechanism is quite different for the two groups. These two groups behave differently in the presence of contour interaction./nThe third study involves comparing a commonly used pediatric visual acuity test, the Cardiff Acuity Test, to measuring vision with the same method used for the other studies - single Lea symbols surrounded by contour bars at half the optotype width away (50%) or the full optotype width away (100%). For 93% of the patients with CVI, 50% and 100% Lea symbols yielded a more reduced acuity compared to the Cardiff Acuity Test; the latter only requires detection of the symbols, whereas the Lea symbols require discrimination between an apple and a house optotype./nFinally, the fourth study examined the relationship between contour interaction and contrast sensitivity in children with CVI. Preliminary findings show a positive correlation between contour interaction and contrast sensitivity. Understanding how object contrast affects contour interaction can be translated into real world recommendations for parents and teachers and can also serve as a basis for designing perceptual learning interventions./nThe overarching goal of this research is to translate measurements into usable interventions to improve the lives of patients with CVI. In general, measuring visual acuity in children with CVI in the presence of contour interaction may give a better understanding of the child's visual potential and could be most useful when making recommendations to the child's family and care team.

Advisor: Orel-Bixler, Deborah