Evidence that unstable vision can cause reading difficulties

The idea that dyslexic children have visual problems is unpopular. However, J.F. Stein and M.S. Fowler, University of Oxford, England, believe that one reason some dyslexic children experience an unstable visual world in which letters and words seem to move around uncontrollably is that they are unable to maintain stable binocular control.

Unstable binocular control is seen in many normal readers, especially young readers. But, stability normally develops as a child matures, usually at the same time the child is learning to read. The authors concede that intelligence and phonological skills probably play a role in how well a child with unstable binocular control learns to read. However, studying exceptionally good readers, they found that only 2 percent exhibited unstable vision.

In studies or normal 8- to 10-year-old readers, about 25 percent show unstable vision, but, when these normal readers with unstable binocular control were tested individually, it was found that although their reading was within the average range for their age, they performed about four to six months below their peers. In addition, Stein and Fowler’s data indicate that nearly two-thirds of children with serious reading problems exhibit visual instability.

Research has shown that covering up one eye improves binocular control. Stein and Fowler report that when researchers are able to improve dyslexic readers’ binocular control, reading improvement often follows – even before these children receive specific remediation in reading. In a study that matched children for initial reading skill and IQ, children with corrected binocular control demonstrated significantly greater reading improvement. Stein and Fowler conclude that these reading gains must be attributed to improved binocular control. However, they do not claim that improving binocular control will cure all reading disability. They believe that it is one cause of serious reading difficulty and that remedial instruction is necessary once a child’s binocular vision has been stabilized.
“Unstable Binocular Control in Dyslexic Children”, Journal of Research in Reading,Volume 16, Number 1, pp. 30-45.

Published in ERN September/October 1993, Volume 6, Number 4.

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