Eye movement dysfunction

What is eye movement dysfunction?

Smooth pursuit eye movement is a visual tracking reflex evoked by a smoothly moving target, usually elicited by stimuli presented on a computer monitor. Deficits in smooth pursuit and an excess of ‘jerky’ eye movements were one of the earliest reported phenotypes associated with schizophrenia, and smooth pursuit has since been identified as a candidate endophenotype (phenotype with a clearer genetic connection) for schizophrenia. The aim of the smooth pursuit reflex is to maintain the image of the moving target on the fovea, the region of the retina with the highest density of photoreceptors. The neural pathways involved in generating smooth pursuit are a complex network from the cortical visual pathways through to the brainstem ocular motor nuclei (III, IV and VI), and consequently an alteration in smooth pursuit performance may not in itself shed light on the actual nature of the dysfunction. Components of smooth pursuit which are quantified include gain in the open and closed loops, as well as rates and amplitudes for both intrusive and anticipatory saccades (fast eye movements). Closed loop gain is an index of temporal synchrony of the eye and the target during pursuit, and is estimated as the ratio of the respective velocities. Open loop gain is the average acceleration during the initiation of pursuit, in the first 100ms. During this period there is no visual feedback and so the movement is solely a result of visual motion signal input. Spontaneous saccades can occur during smooth pursuit: these can either be anticipatory saccades which facilitate movement towards the target, such as reflexive visually guided saccades; or intrusive saccades, which interrupt the smooth tracking of the target, such as catch-up saccades, back-up saccades, and memory-guided saccades.

What is the evidence on eye movement dysfunction?

Moderate to high quality evidence suggests reduced eye tracking performance in people with schizophrenia compared to controls, particularly in maintenance (closed loop) gain. Moderate quality evidence also suggests increased saccadic intrusion during eye tracking, with the effect largest for leading saccades and catch-up saccades. High quality evidence suggests relatives of people with schizophrenia also show impairment in closed loop gain during smooth pursuit eye movement. Moderate quality evidence suggests they show increased error rate of visually and memory guided saccades, impairment in fixational stability, and increased intrusive anticipatory saccades during smooth pursuit eye movement.

March 2019

Last updated at: 12:25 am, 28th March 2019
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Orange - Topic summary is being compiled.
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