An investigation of the contrast sensitivity in dyslexic children

A review of the neurophysiological studies suggests that dyslexia is the result of a deficit in the magnocellular part of the visual system. Most of the evidence cited in favour of this hypothesis is from contrast sensitivity studies. This study tested the hypothesis that visual processing deficits may be present in dyslexia by comparing the visual contrast sensitivity of dyslexic children and controls. contrast thresholds were recorded in 67 children، 26 dyslexic (mean age of 8. 76±1. 33) and 41 control group (mean age 9. 07±1. 40). Contrast sensitivity was measured using Freiburg acuity and contrast test (FrACT) version 3. 7 at frequency 5cpd in both eyes. The results were then analyzed using SPSS-18. mean contrast threshold of Right eyes in dyslexic group (0. 62±0. 12) and control group (0. 68± 0. 15)، mean contrast threshold of Left eyes in dyslexic group (0. 61±0. 16) and control group (0. 67±0. 15) were measured. There were no statistically significant differences between two groups in ight eyes (pvalue: 0. 279) and in left eyes (pvalue: 0. 124). The present study do not support the hypothesis of magnocellular visual pathway deficit in dyslexia. Our result show that there isn’t relationship between reading ability and contrast sensitivity in dyslexic children.