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On the basis of present knowledge of the distribution of natural haze particles in the atmosphere, the relation between the back-scatter intensity and the visual range on the extinction coefficient has been analyzed. It can be shown that the various processes which cause the changes in visibility (increasing haze-particle number, change in haze particle-size distribution, etc.) result in rather different back-scatter conditions. Therefore, it cannot be expected that a unique relation between visibility and back-scatter signal can be found. A relation, visibility = f(back-scatter signal), with useful accuracy can be established only for specific atmospheric conditions; this relation, however, may be characteristic for certain geographical areas. These conclusions, derived from natural aerosol distributions and processes, are found to be in agreement with some published empirical data on scattering and visibility correlation. (Author).
The current leading cause of visual impairment among children is not a disease or condition of the eyes, but cortical visual impairment (CVI)-also known as cerebral visual impairment-in which visual dysfunction is caused by damage or injury to the brain. The definition, nature, and treatment of CVI are the focus of great concern and widespread debate, and this complex condition poses challenges to professionals and families seeking to support the growth and development of visually impaired children. On the basis of more than 30 years' experience in working with hundreds of children of all ages with CVI, Christine Roman-Lantzy has developed a set of unique assessment tools and systematic, targeted principles whose use has helped children learn to use their vision more effectively. This one-of-a-kind resource provides readers with both a conceptual framework with which to understand working with CVI and concrete strategies to apply directly in their work.