Disturbance of Slow Component of Eye Movements

Abstract

Eye movements are very important indexes for evaluating vestibular disorders or neurological diseases. Eye movements are composed of two factors, slow and quick movements.
The slow component of eye movements is evaluated by pursuit eye movements or by the slow phase of optokinetic nystagmus (OKN). When the slow component of eye movements is impaired, smooth pursuit is disturbed, so it is saccadic or ataxic. Also, the slow phase of optokinetic nystagmus is flat without increase of velocity as the OKN drum velocity increases with or without spiky movements.
Disturbances of the slow component of eye movements are the following two types :
1) The slow component of eye movements itself is disturbed.
Pursuit eye movements are seccadic or ataxic, and the slow phase of the optokinetic nystagmus pattern (OKP) is flat with spiky movements in the slow phase direction. This type is seen in patients with cerebellar lesions.
2) Both slow and quick components of eye movements are disturbed.
Pursuit eye movements are saccadic, and the slow phase of OKP is flat and without spiky movements. This type is seen in patients with pontine lesions.