Vertical and Oblique Saccade Disconjugacy in Strabismus

Abstract

These data indicate that the assessment of saccade disconjugacy in strabismus may yield misleading results if direction is not considered. The complex pattern of disconjugacy suggests that strabismus is associated with substantial abnormalities within the circuitry controlling saccades. Neurophysiological studies are needed to identify the specific neural substrates for these behavioral effects.

Saccadic latency in amblyopia

“…For example, the two eyes make saccades that differ in size and direction both in strabismic humans (Bucci, Kapoula, Yang, Roussat, & Bremond-Gignac, 2002; Maxwell, Lemij, & Collewijn, 1995) and strabismic monkeys (Fu, Tusa, Mustari, & Das 2007; Walton, Ono, & Mustari, 2014). The most striking oculomotor feature of a strabismic amblyope is the degree of unsteadiness when fixating with the amblyopic eye (Cuiffreda, Kenyon, & Stark, 1979; Gonzalez, Wong, Niechwiej-Szwedo, Tarita-Nistor, & Steinbach, 2012; Maxwell et al, 1995; Schor & Hallmark, 1978; Zhang et al, 2008).…”

Longitudinal Evaluation of Eye Misalignment and Eye Movements Following Surgical Correction of Strabismus in Monkeys

“…4–6 These animal models have been very effective in replicating a variety of strabismus oculomotor features beyond just horizontal misalignment, such as dissociated deviations, latent nystagmus, fixation instability, fixation switch behavior, naso-temporal asymmetry of horizontal smooth-pursuit and optokinetic nystagmus, and disconjugate eye movements. 6–16 Studies in animal models have also led to several insights into neural strabismus mechanisms including identifying neural substrates for misalignment, A/V patterns, and saccade disconjugacies. For example, previous studies from our laboratory and others have shown that, in monkeys with a sensory strabismus, an innervational drive from the motor nuclei (oculomotor and abducens nucleus) plays a critical role in setting the state of ocular misalignment on a moment-to-moment basis.…”

Misdirected horizontal saccades in pan-cerebellar atrophy

“…The authors suggested that non-human primates reared with visual deprivation during initial days of life develop A-and V-pattern strabismus and dissociated vertical deviation. These animals also have cross-coupled eye movement but only in non-viewing eye [27,28]. The authors also found the evidence for abnormal neural signals in burst tonic motor neurons driving cross-axis eye movements.…”

“…The authors also found the evidence for abnormal neural signals in burst tonic motor neurons driving cross-axis eye movements. Hence, they put forward a hypothesis that changes in neural connectivity in midbrain and sub-cortical ocular motor nuclei cause the pattern strabismus and cross-coupled eye movements in their animal model [27,28]. Similar cross-coupling was also seen in optokinetic nystagmus in monkeys with infantile strabismus [29].…”

“…The animal models with A-and V-pattern strabismus and dissociated vertical deviation offered an alternate hypothesis for cross-coupled eye movements [27,28]. The authors suggested that non-human primates reared with visual deprivation during initial days of life develop A-and V-pattern strabismus and dissociated vertical deviation.…”