Learning Diversity in the Chinese Classroom: Contexts and Practice for Students with Special Needs

8 - Students with Visual and Perceptual Difficulties

8 Students with Visual and Perceptual Difficulties Simon LEUNG and Phoebe YEUNG In this chapter, the following topics are discussed: • The definition of visual impairment, its main causes among children, and pertinent factors that affect their learning; • The diversity amongst visually impaired students because of the diverse nature and different degrees of severity of particular impairments; • The various challenges that visually impaired students have to face in the classroom, such as medium of learning, and other restrictive conditions posed by the environment; • Common classroom strategies for adaptation of study skills, teaching materials, presentation methods, assignments and assessments; and • Practical suggestions for the teaching of languages, social studies, science, mathematics, information technology, visual arts, music, physical education and home economics. Introduction Visual impairment poses significant obstacles to a child’s learning because learning is normally dependent on visual information. In order to be able to assist a visually impaired student in the classroom, teachers have to understand the nature of visual impairments and the various effects they have on the child. This chapter explains how visual impairment is defined, and the causes and effects of various visual impairments, and then describes relevant strategies for teachers to work effectively with blind or low vision students in the classroom. 250 Simon LEUNG and Phoebe YEUNG Definitions of Visual Impairment Visual impairment is defined by two main factors, namely visual acuity and visual field. Visual acuity denotes how clearly a person sees. The degree of visual impairment is determined using a vision test and the results are typically represented as a ratio. A ratio of 6/60, for example, means that the person can see an object at a distance of six meters compared to a normally sighted person who can see the same object at sixty meters. Visual field is the extent of the area that can be seen. While the eye is focused on a central point straight ahead, the visual field of a person with normal sight is about 150 degrees. A person with a visual field of less than 20 degrees is considered legally blind, irrespective of the visual acuity. The World Health Organization (2004) defines visual impairment in the following way: • A person with low vision has a visual acuity between 6/18 and 3/60. • A person who is blind has a visual acuity less than 3/60 or a visual field of less than 20 degrees. In Hong Kong, visual impairment is of two broad types: blindness and low vision, where blindness refers to the absence of any visual function, meaning that the person has a complete absence of light perception. Low vision is categorized into three subgroups: (1) severe low vision (visual acuity of 6/120 or worse, or a contracted visual field of less than 20 degrees); (2) moderate low vision (visual acuity of 6/60 to better than 6/120); and (3) mild low vision (visual acuity of 6/18 to better than 6/60) (Hong Kong Government, 1999). Anatomy of the Human Eye The human eye is composed of a number of distinct segments, reflecting their different functions. It is a sphere with a diameter of about 2.4 cm (Saladin, 2004, pp. 612–5). The outer layer forms the wall of the eyeball and includes the sclera and the cornea. The cornea is transparent and its function is to refract and admit light, while the sclera, consisting of connective tissue, blood vessels and nerves, helps to support the shape of the eye. The middle layer consists of the choroids, a deeply pigmented layer of tissue, the ciliary body and the iris. The ciliary body supports and adjusts the lens and secretes a fluid, and the iris adjusts the amount of light entering the eye by adjusting its diameter. The inner layer consists of the retina, supporting the photoreceptive cells, and the optic nerve. Students with Visual and Perceptual Difficulties 251 Within the eyeball there is a transparent jelly called the vitreous body, and the structure within it is the hyaloid canal. The macula and fovea produce detailed images because of the relatively high density of photoreceptor cells. The blind spot, a region without photoreceptor cells, is found where the optic nerve is attached to the eyeball. Figure 8.1 The human visual system Causes of Visual Impairments Visually impaired students are not a homogeneous group of people. Different visual conditions may involve totally different needs and requirements. Teachers should know...