The influence of the vergence system on strabismus diagnosis and management.

The vergence system is an important element in human eye movement control. It comprises horizontal, vertical, and torsional components, the largest of which is convergence. Vergence performance is largely involuntary, although voluntary effort can influence convergence. Vergence function can be damaged by trauma or organic disease and, because convergence can be exerted voluntarily, it is susceptible to purposeful subjective disturbances. Vergence function is important in the maintenance of binocular control, being synonymous with motor fusion. The most common vergence dysfunction affects convergence and may be exhibited as an excess or weakness such as convergence spasm or paralysis. Divergence dysfunction generally presents with diminished function such as divergence weakness; vertical and cyclovergence disturbances are rare. An update is given on the neuroanatomical areas that subserve the vergence system. Clinical examples of the most common vergence disorders are presented. The influence of the vergence system on the diagnosis and management in common and less well-known clinical entities is described and discussed.