Double-blind placebo-controlled examination of timing effects in the training of positive vergences.

The purpose of this study was to document the effects of positive fusional vergence therapy and to determine the most effective timing of such training. Four experimental protocols were selected and five subjects were assigned randomly to each of the four experimental groups. Each subject in each group spent 120 min (total) over a period of 3 weeks doing positive fusional vergence training. Group A trained in twelve 10-min sessions; group B in six 20-min sessions; and group C in three 40-min sessions. Group D was a control group. All the training was in-office and consisted of positive fusional vergence training on the synoptophore. Each of the test groups showed increases in their positive fusional vergence ability at both distance and near. Group A (shorter sessions) demonstrated the largest increases overall. In addition, the group which trained in short 10-min sessions (Group A) was the only one which showed significant increases in the negative fusional vergences and the positive blur finding. I conclude that it is best to use short, frequent training sessions to increase the amplitude of positive fusional vergence. The results and implications of the study are discussed briefly.