Convergence

Abstract

IONDONCONVERGENCE may be summarised as consisting of three parts, tonic, accommodational, and fusional (Maddox). Tonic convergence is that amount of fusional innervation which is necessaryr to place the eves in the position of parallelism at infinity.The Accommodational convergence results from, and is associated with, any accommodational effort. These two functions are interconnected; contraction of the ciliarv muscles is accompanied by a known and measurable amount of convergence. The contraction of the ciliaries may be insufficient or too great, but convergence must be exact for any point within infinitv, to avoid diplopia. At the near point (33 cms.) eighteen prism dioptres are required, and as accommodation is variable, the final adjustment is known as fusional convergence.If accommodational convergence is insufficient fusional convergence is positive (adductive), if it is excessive fusional convergence is negative (abductive).All lateral muscle imbalances are errors of convergence, and all tests are convergence tests. Fusional convergence is the innervation, whichi corrects near point imbalances. In order to judge w\'hether or not anv-imbalance, either at distance or near, requires hlelp to maintain efficiency, the exact futsionzal reserve which the patient possesses must be know\n.The fusional amplitude can be ascertained by taking the patient's duction, which roughly represents the fusional amplitude, which may enable himn to cope with the imbalance.Anv imbalance at the near point is always the difference between that measured at distance and that found at the near point (33 cms.). For example if three dioptres of exophoria is found at distance and five dioptres at near, the sum total of the near imbalance is two dioptres of exophoria, whereas if three dioptres of esophoria exists at distance and five dioptres of exophoria at near, the sum total will be eight dioptres of exoplhoria at the near point.

A review of non-strabismic accommodative-vergence anomalies in school-age children. Part 1: Vergence anomalies

“…The review is of school-age children between 6 and 18 years of age, and the focus is on aspects of the epidemiology of AVAs. A few classic papers published in the early 1990s 29,30,31,32,33,34 were considered, so as to relate previous concepts to current understanding. The review is presented in two parts.…”

“…39 In normal eyes, accommodation and convergence are neurologically coupled. 31,44 Convergence results from, and is associated with, any accommodation effort; hence contraction of the ciliary muscles to mediate accommodation is accompanied by an amount of convergence. 31,32,33,34,44 Contraction of the ciliary muscles may be insufficient or excessive but convergence must be exact for any point closer than infinity to avoid diplopia.…”

“…31,44 Convergence results from, and is associated with, any accommodation effort; hence contraction of the ciliary muscles to mediate accommodation is accompanied by an amount of convergence. 31,32,33,34,44 Contraction of the ciliary muscles may be insufficient or excessive but convergence must be exact for any point closer than infinity to avoid diplopia. 31 Owing to this stable and positive link between accommodation and convergence, 33,34 a deficiency in one variable may affect the other.…”

“…31,32,33,34,44 Contraction of the ciliary muscles may be insufficient or excessive but convergence must be exact for any point closer than infinity to avoid diplopia. 31 Owing to this stable and positive link between accommodation and convergence, 33,34 a deficiency in one variable may affect the other. 31,44 PCI has been described in the literature 39,44 as a vergence anomaly that results from a person's inability to convergence as a result of insufficient accommodative ability.…”

“…31 Owing to this stable and positive link between accommodation and convergence, 33,34 a deficiency in one variable may affect the other. 31,44 PCI has been described in the literature 39,44 as a vergence anomaly that results from a person's inability to convergence as a result of insufficient accommodative ability. 12 This syndrome has been attributed to a central nervous defect that affects the accommodative and convergence mechanism.…”