Objective Visual Accuity Test Using Optokinetic Nystagmus

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The aim of this research is to examine the possibility of Optokinetic Nystagmus (OKN) as an objective visual acuity test for sever-multiple handicapped children and infants. We measured the OKN of 30 mentally retarded children induced by turning drum. The result appeared to be affected by attention of children or aversive response. Then we examined what conditions need to measure the visual acuity from OKN.How do visual target size and speed affect inducing OKN under normal sighted condition, refractive error condition, opacity condition and visual field defect condition ? Under normal sighted condition, the more thin the target size is, the more slowly the target need to move for OKN to be induced. When the target size is 25', the target speed is 500-750Hz for inducing OKN.But, the target 25' size is 0.04 as visual acuity. So we need two parameters to speculate the visual acuity from OKN.These are target size and speed. Under refractive error and opacity condition, when the target size is thin, we need more slow target speed. In addition to the visual acuity, other visual factors affect the amplitude of OKN and the time of one cycle.We conclude from this research that OKN is very useful clinical method as visual acuity test for sever-multiple handicapped children. So we need OKN research under various visual handicapped conditions still more.