Diagnosis of dyslexia by means of a new indicator of eye dominance

SUMMARY Many dyslexic children are unable accurately to control the movements of their eyes even when they are not trying to read. This immaturity helps to explain their visual confusions. It may result from failure to develop dependable associations between retinal and ocular motor signals. These are essential to fix the true, as opposed to retinotopic, locations of objects in the outside world. We have used a new test to study retinal/ocular motor correspondence in dyslexic children and age/IQ matched normal readers. motor dominance. The idea that developmental dyslexia is ever the result of a primary visual disorder is not at present popular because conventional tests rarely reveal any disorder of a dyslexic's eyesight, while thousands of children with profoundly abnormnal vision neverthe-less learn to read successfully. Dyslexia is generally held to be a general cognitive defect rather than a perceptual one.' Dyslexia is, however, often associated with abnormal movements of the eyes.23 Although many people suggest that these are merely a consequence rather than a cause of reading difficulties, perhaps arising from children's inability to make sense ofwhat they see,4 it is now clear that many dyslexics have unusual eye movements even when they are not trying to read. They are more likely than normal readers to show esophoria,5 convergence insufficiency,6 breakdown to saccadic jerks (cogwheeling) during attempts at smooth pursuit,7 excessive numbers of regressions, and inability to maintain stable fixation when viewing sequentially illuminated light-emitting diodes.8 These eye movement disorders may help to explain a child's difficulties with learning to read. Reading demands highly accurate ocular motor control, together with precise monitoring of eye position, since this is essential to determine true visual direction. When we look at a letter we can estimate its true position in space only if we know the exact angle of our gaze. The positions of the images of the lette