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SPED 537 ECSE Methods Multiple Disabilities Chapter 4 March 13-14, 2006 Deborah Chen, Ph.D. CSU, Northridge
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Incidence of Visual Impairments 1 in 3000 children 46% congenital 38% vision loss in 1 st year of life 25 % totally blind 25 % light perception 50% functional vision
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Definitions Legally blind Totally blind Light perception Form perception Partially sighted Low vision
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Types of Visual Impairment Decreased visual acuity Field loss Loss of contrast sensitivity Color blindness Ocular-motor problems Cortical visual impairment Delayed visual maturation
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Causes of Acuity Loss Retinopathy of Prematurity Cataracts Nystagmus Refractive errors Strabismus
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Refractive Errors Myopia Hyperopia Astigmatism
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Strabismus Esotropia Exotropia Hypertropia Hypotropia
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Clinical Vision Tests: Fixation and Eye Alignment Versions Hirshberg Krimsky Unilateral and alternating cover test Base-out prism
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Clinical Vision Tests Pupillary response Vestibular ocular reflex (VOR)- similar to Optokinetic Nystagmus (OKN) test Refractive Error
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Behavioral Tests Contrast sensitivity Color vision Depth perception Visual fields Visual acuity (Teller Cards)
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Electrophysiological Tests Visual Evoked Potential (VEP) or Visual Evoked Response (VER) Electroretinography (ERG)
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Checking for Ocular Health Examines the front and back structures, retinal, optic nerve
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Ocular Visual Impairment Atypical eye exam Consistent visual attention Nystagmus Restrictions of visual fields Occasional photophobia Eye pressing Occasional head shaking Light gazing
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Cortical Visual Impairment Normal eye exam Variable vision Short visual attention No nystagmus No head shaking No eye pressing Light gazing Photophobia in 1/3 cases ( Dr. J. Jan, Children’s Hospital, Vancouver, B.C. Canada)
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Visual Responses Awareness Attention Understanding Fixation Tracking Peripheral Central Simple Complex
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Visual Responses Awareness Attention Understanding Large Small Familiar Unfamiliar Near Far
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Visual Stimuli Preferred: Objects with lights or movement Geometric designs High contrast materials Bright colors Familiar: Family members Clothing, utensils, household items Toys Pictures
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Visual Saliency Motivation factors Lighting (natural, indoor, outdoor, dark) Position (placement of target) Distance from child Highlight or contrast Illumination of target Characteristics of target
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