Prisms throw light on developmental disorders.

Prism adaptation, in which the participant adapts to prismatic glasses that deflect vision laterally, is a specific test of cerebellar function. Fourteen dyslexic children (mean age 13.5 years); 14 children with developmental coordination disorder (DCD): 6 of whom had comorbid dyslexia; and 12 control children matched for age and IQ underwent prism adaptation (assessed by clay throwing accuracy to a 16.7 degrees visual displacement). All 8 DCD children, 5 of the 6 children with comorbid DCD and dyslexia and 10 of the 14 dyslexic children showed an impaired rate of adaptation, thereby providing strong evidence of impaired cerebellar function in DCD and developmental dyslexia. Taken together with other emerging evidence of overlap between developmental disorders, these findings highlight the importance of complementing research on the individual disorders with research on the commonalities between the disorders.