Fine binocular control in dyslexic children.

Dyslexic children often complain that letters seem to move around. The hypothesis advanced here is that this is a symptom of immature vergence control which leads to an unstable sense of visual direction. Evidence is presented that (1) sixty-seven per cent of dyslexic children exhibit poor dynamic control of vergence movements in response to a small fusion stimulus, (2) most good readers have good vergence control, (3) children with poor vergence control have reduced stereoacuity, (4) six months monocular occlusion for reading and close work assisted 51 per cent of dyslexics with unstable vergence control to improve; thereafter their reading improved rapidly also. It is concluded that defective vergence control is an important, though not the only, cause of dyslexics' problems.