SPED 537 ECSE Methods Multiple DisabilitiesChapter 4

March 13-14, 2006Deborah Chen, Ph.D.

CSU, Northridge

Incidence of Visual Impairments 1 in 3000 children 46% congenital 38% vision loss in 1st year of life 25 % totally blind 25 % light perception 50% functional vision

Definitions Legally blind Totally blind Light perception Form perception Partially sighted Low vision

Types of Visual Impairment Decreased visual acuity Field loss Loss of contrast sensitivity Color blindness Ocular-motor problems Cortical visual impairment Delayed visual maturation

Causes of Acuity Loss Retinopathy of Prematurity Cataracts Nystagmus Refractive errors Strabismus

Refractive Errors Myopia Hyperopia Astigmatism

Strabismus Esotropia Exotropia Hypertropia Hypotropia

Clinical Vision Tests: Fixationand Eye Alignment Versions Hirshberg Krimsky Unilateral and alternating cover

test Base-out prism

Clinical Vision Tests Pupillary response Vestibular ocular reflex (VOR)-

similar to Optokinetic Nystagmus (OKN) test

Refractive Error

Behavioral Tests Contrast sensitivity Color vision Depth perception Visual fields Visual acuity (Teller Cards)

Electrophysiological Tests Visual Evoked Potential (VEP) or

Visual Evoked Response (VER)

Electroretinography (ERG)

Checking for Ocular Health

Examines the front and back structures, retinal, optic nerve

Ocular Visual Impairment Atypical eye exam Consistent visual attention Nystagmus Restrictions of visual fields Occasional photophobia Eye pressing Occasional head shaking Light gazing

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)

Visual Responses

Awareness Attention Understanding

Fixation Tracking

Peripheral Central

Simple Complex

Visual Responses

Awareness Attention Understanding

Large Small

Familiar Unfamiliar

Near Far

Visual Stimuli

Preferred: Objects with lights or movement Geometric designs High contrast materials Bright colors

Familiar: Family members Clothing, utensils, household items Toys Pictures

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