The systematic examination of eye movements is summarized in Table 1. The most useful part of the examination concerns saccades, which are the rapid eye movements by which we voluntarily move our line of sight (direction of gaze). Saccades are perhaps the best understood of all movements both in terms of their dynamic properties and neurobiology (1-3). It is important to differentiate between limited range of movement, especially upward, and speed of saccades, especially vertically. Normal elderly subjects show limited upgaze (4), and this may be because of changes in the connective tissues of the orbit (5). Nonetheless, some normal elderly subjects make vertical saccades that have normal velocities, within their restricted range of motion (6). Range of movement is conventionally elicited as the patient attempts to follow the examiner's moving finger, but this does not test saccades. It is important to ask the patient to shift gaze on command between two stationary visual targets, displaced horizontally or vertically, such as a pencil tip and the examiner's nose. After each verbal cue (e.g., "look at the pencil; now look at my nose"), note the time taken to initiate the saccade, its speed, and whether it gets the eye on target, or whether further corrective saccades are needed. It is also useful to ask parkinsonian patients to make saccades voluntarily at a rapid pace back and forth between two stationary targets (e.g., a finger from the left and right hand of the examiner. Patients with idiopathic Parkinson's disease (PD) often have difficulty making such self-generated sequences and several saccades, rather than one, are needed for the eye to reach the target (see video 1 on accompanying DVD).
From: Current Clinical Neurology: Atypical Parkinsonian Disorders Edited by: I. Litvan © Humana Press Inc., Totowa, NJ
Another important feature of many parkinsonian disorders is inappropriate saccades that intrude on steady fixation; the most common are small "square-wave jerks" that are most easily appreciated during ophthalmoscopy as to-and-fro movements of the fundus. Smooth pursuit is not usually helpful, because many elderly normal subjects and even some younger subjects may have impaired pursuit that requires catch-up saccades to keep the line of sight on the moving target. Optokinetic stimulation at the bedside may be useful in some patients who have difficulty initiating voluntary saccades (e.g., progressive supranuclear palsy [PSP]); vertical drum motion may induce tonic vertical deviation of the eyes in affected individuals or evoke reflexive "quick phases" of nystagmus. Vergence is also often impaired in normal elderly subjects, and identification of abnormalities may require laboratory assessment.
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