Role of Ocular Motor Assessment 235 235 From: Current Clinical Neurology: Atypical Parkinsonian Disorders Edited by: I. Litvan © Humana Press Inc., Totowa, NJ 15 Role of Ocular Motor Assessment in Diagnosis and Research R. John Leigh and David S. Zee INTRODUCTION The clinical evaluation of eye movements can contribute substantially to the diagnosis of parkin- sonian disorders, provided the physician performs a proper examination and interprets the findings by referring to a simple scheme of the neurobiology of eye movements (1). Further diagnostic infor- mation can often be obtained by recording eye movements, which are more accessible to measure- ment and analysis than limb movements or gait. A good part of the neurobiological substrate of eye movements has been defined, which makes it possible to attribute disordered properties of eye move- ments to dysfunction of specific neuronal populations or structures in the brain. In this chapter, first, we review pertinent aspects of the ocular motor examination; second, we highlight some important test paradigms and technical aspects of measuring eye movements; and third, we summarize disor- ders of ocular motility reported with parkinsonian disorders and diseases affecting the basal ganglia. CLINICAL EXAMINATION OF EYE MOVEMENTS IN PARKINSONISM 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 connec- tive 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 conven- tionally 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).