Timothy C. Hain, MD•Page last modified: February 26, 2017
Divergence insufficiency, divergence paralysis, and divergence excess, are poorly understood entities.
This was first described as a clinical entity by Parinaud in 1883. Since then it has been reported in several neurologic diseases, especially conditions raising intracranial pressure such as tumor, pseudotumor, aqueductal stenosis, intracranial hematoma or head trauma (Hogg and Schoenberg, 1979; Rutkowski and Burian, 1972). These are generally entities that might affect 6th nerve function. Although not well documented in the literature, we have seen several cases with divergence insufficiency with the Chiari malformation.
Bielschowsky (1940) defined the diagnostic criteria for divergence insufficiency. There is esotropia with uncrossed diplopia during attempted fixation of a distant object. Single vision is obtained during fixation of objects located at about ten to twenty inches; more proximal fixation may cause crossed diplopia (due to associated convergence insufficiency). Horizontal motion of the eyes may be normal; the diplopia is unchanged or may even disappear on lateral gaze.
Guyton (2006) suggested that there may be "occasional divergence insufficiency in presbyopes". Schor (1988) suggested that "extremely high and low categories of accommodative vergence may result from adaptive disorders of accommodation and convergence. " It appears that Schor was suggesting that divergence disorders might be related to "adaptive disroders of accomodation and convergence.
Paresis of divergence must be differentiated from bilateral sixth nerve palsy, convergence spasm, and decompensated strabismus. Excluding bilateral lateral rectus palsies may be particularly difficult, as a subtle lateral rectus weakness may be difficult to document.
Kirkham, Bird and Sanders (1972) demonstrated that saccadic velocities of the abducting eye were low in some patients with divergence paralysis, even though the range of motion was full. They hypothesized that "minimal interference of sixth nerve function by raised intracranial pressure may produce the features of divergence paralysis without other evidence of sixth nerve palsy". Whether divergence paralysis may occur in the absence of measurable saccadic slowing is uncertain.
This is similar to bilateral medial rectus palsies, and manifests with exophoria or exotropia. It is far better tolerated than divergence paralysis, because subjects can simply use their intact convergence system to overcome diplopia. According to Lim et al (2011), divergence excess contributes to more than half of exotropia cases.
This page is based on a a review article by Hain and Zee (1989), with updates.