On the origin of visual dyslexia.

Analysis of the binocular co-ordination errors of a young dyslexic reveals a simple optical explantation for one of two types of letter confusion found in dyslexia. Although binocular control was grossly abnormal in reading, no ocular defect could be found in standard ophthalmic and orthoptic tests. Re-examination of the same patient six years later, again showed no ocular defect on normal testing but binocular movements in reading, while still abnormal, showed no trace of the striking original defect. This complete masking of the original condition with time must severely restrict the value of mass surveys of established dyslexics.