A review of convergence insufficiency: what are we really accomplishing with exercises?

INTRODUCTION Orthoptic exercises have been the primary treatment for convergence insufficiency since this condition's first description in 1855. It is presumed that exercises work by improving fusional convergence. In recent years, research from eye movement laboratories has challenged our theories on the nature and dynamics of convergence, the effect of convergence exercises, and the etiology of primary convergence insufficiency. METHODS A review of the ophthalmological, optometric, and basic science literature was done to retrieve the most recent research on vergence eye movements and convergence insufficiency. RESULTS Convergence appears to be a bi-phasic response to a change in stimulus position in depth. The first phase, which may represent the contribution of proximal convergence, is not under visual feedback, is fast with a short latency, and is triggered by stimuli moving rapidly in depth or by large, sudden changes in fixation. This phase is followed by a slow vergence movement with a slightly longer latency, triggered by small disparity vergence errors. The second phase is under the control of visual feedback, and represents the contributions of fusional and accommodative convergence. Eye movement recordings indicate that the velocity and amplitude of the first phase of convergence are temporarily adaptable with exercises. The second phase does not appear to be amenable to training. Tonic convergence is also trainable. CONCLUSION Convergence exercises are effective in temporarily improving the dynamics of proximal and tonic convergence, but have little effect on fusional or accommodative convergence.