Ocular motor abnormalities in neurodegenerative disorders

Abstract

Eye movements are a source of valuable information to both clinicians and scientists as abnormalities of them frequently act as clues to the localization of a disease process. Classically, they are divided into two main types: those that hold the gaze, keeping images steady on the retina (vestibulo-ocular and optokinetic reflexes) and those that shift gaze and redirect the line of sight to a new object of interest (saccades, vergence, and smooth pursuit). Here we will review some of the major ocular motor abnormalities present in neurodegenerative disorders.

Figure 1

Schematic illustration showing two pathways projecting to superior colliculus (SC) via pars reticulate (SNpr), termed the direct and indirect pathways. Excitatory projections to the caudate from the frontal cortex trigger saccades via the indirect pathway. CD inhibits the SNpr, which tonically inhibits the SC. Excitation of CN could lead to disinhibition of SC and thus generation of saccades. The direct pathway may mediate saccade initiation by decreasing GABAergic connections within the SC. A possible mechanism by which HD interferes with saccades is by disruption of the indirect pathway as shown at the point marked X; (−) inhibitory, + excitatory.