Lecture 4b - Lecture 4. B) Children with Visual Impairments...

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Lecture 4. B) Children with Visual Impairments – Classification, prevalence and etiology Definitions - Visual impairment: ranges from mild visual impairment to total blindness - Low vision: person’s corrected vision is lower than normal o Distance acuity is 20/70 or less in the better eye - Blindness: very little to no sight o A distance of acuity of 20/200 or less in the better eye o Visual field is reduced to an angle of 20 degrees or less at its widest diameter - Visual acuity: the measure of the smallest image distinguishable by the eye - Visual field: the entire area that can be seen when staring straight ahead; reported in degrees - Snellen chart o 1862, Herman Snellen o Acuity measured begin with 20/20 vision o Series of letters, numbers or symbols that must be read from a distance of 20 feet o Each line is a different size o V = d/D; V= visual acuity, d = distance, D = distance at with levels are clearly read - Visual functioning: refers to what a visually impaired person does with his/her residual vision o I.e. some may be able to discern light, colour or shapes while others could be able to read but seeing clearly in one small area but have difficulty getting around
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Lecture 4b - Lecture 4. B) Children with Visual Impairments...

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