Slow conjugate eye movements: Normative data for routine diagnosis of ophthalmo-neurological disorders

Horizontal gaze nystagmus: a review of vision science and application issues

The Horizontal Gaze Nystagmus (HGN) test is one component of the Standardized Field Sobriety Test battery. This article reviews the literature on smooth pursuit eye movement and gaze nystagmus with a focus on normative responses, the influence of alcohol on these behaviors, and stimulus conditions similar to those used in the HGN sobriety test. Factors such as age, stimulus and background conditions, medical conditions, prescription medications, and psychiatric disorder were found to affect the smooth pursuit phase of HGN. Much less literature is available for gaze nystagmus, but onset of nystagmus may occur in some sober subjects at 45 degrees or less. We conclude that HGN is limited by large variability in the underlying normative behavior, from methods and testing environments that are often poorly controlled, and from a lack of rigorous validation in laboratory settings.

Deficits in ocular and manual tracking due to episodic ataxia type 2

Four patients with a novel mutation leading to episodic ataxia type 2 were studied in a task that required them to track target motion either with the eyes or with the index finger of the right hand. The target initially moved in a straight line and then changed direction at an unpredictable time by an unpredictable amount. On the day of testing, 3 of the patients were evaluated as normal on a neurological exam, whereas the fourth was severely ataxic. Nevertheless, all 4 showed deficits in tracking behavior with common features. Ocular tracking tended to result in hypermetric saccades at longer than normal latencies. Smooth pursuit tracking was absent in 1 patient and had lower than normal gain in the others. Deficits in manual tracking showed similarities to the deficits in ocular tracking, with hypermetric compensations for changes in target direction. The similarities in the deficits in manual and ocular tracking suggest that they are subject to similar control by the cerebellar structures.

Eye tracking in normals: spem asymmetries and association with schizotypy

SPEM was recorded electro-oculographically during visual tracking of sinusoidal targets oscillating at .4 and .8 cycles per second in one hundred nineteen undergraduates. The logarithms of median root mean square values were used to assess tracking accuracy for leftward and rightward halfcycles of tracking. Over the entire sample, there was a significant superiority of rightward over leftward tracking, which, given evidence for the ipsilateral mediation of SPEM at the cortical level, suggests a right hemisphere predominance in the control of SPEM in normal subjects. Individual tracking asymmetry was associated with overall tracking accuracy such that subjects with relatively deficient leftward tracking and those with a larger absolute magnitude of asymmetry had poorer overall tracking. High scores on an MMPI schizotypy measure (Sum 2-7-8-0) were significantly related to poorer overall SPEM accuracy, individual tracking asymmetry, the absolute magnitude of tracking asymmetry, and phase lag, though the subjects' sex, handedness, and crossed hand-foot dominance were found to affect the relationships between schizotypy and tracking accuracy. These findings suggest that although control of SPEM may be predominantly right hemispheric, in some persons with a vulnerability to schizophrenia spectrum disorders, expressed as poorer overall SPEM accuracy and high schizotypy scores, left hemisphere-mediated (leftward) SPEM may be particularly impaired.

Computerized analysis of eye movements as a function of age

Vertical and horizontal saccadic (SEMv, SEMh) and smooth pursuit eye movements (SPEM) were recorded in 66 normal subjects of different ages using a computerized system. No difference was found in SEMh recordings for the right versus the left eye or for gaze direction. In contrast, SEMv recordings of upgaze vs. downgaze showed a significant difference in performance index (peak velocity) and delay. SEMh and SEMv performance index and delay were significantly slowed in elderly subjects, although accuracy was not affected. SPEM analysis also revealed a decrease in velocity in elderly people indicating diminished tracking ability as a result of the aging process. These data suggest that senescence may influence some SEM and SPEM parameters. We thus emphasize the usefulness of having reliable normative data corrected for age.

Concordance of smooth pursuit and saccadic measures in normal monozygotic twin pairs

Although the range of normal ocular motor performance is broad, little is known about the sources of variability. Genetic transmission of eye movement deficits has been described but such possible control of normal function has been little investigated. Characteristics of smooth pursuit and saccades can be examined for the degree of concordance in related individuals. In this pilot study, we studied saccades and pursuit in eight monozygotic (MZ) twin pairs. The statistical analysis of the data used the intraclass correlation of MZ twins (rMZ) to estimate what fraction the covariance of the twin pairs was of the population variance. All saccadic measures showed significant MZ correlations (p < 0.05). Smooth pursuit gains were even more highly correlated (p < 0.001). These results indicate considerable similarity within pairs of twins, particularly for horizontal smooth pursuit, and suggest that larger studies on monozygotic and dizygotic twins would be desirable, to help separate out the relative contributions of environmental and genetic factors.

A clinically oriented approach to smooth pursuit eye movement quantitative evaluation

The electrooculographic technique was used to record smooth pursuit eye movements in 71 healthy subjects homogeneously distributed within an age range between the 2nd and the 6th decades. The target moved at constant velocity (triangular ramps) and 9 different target velocities (V), from 10 deg/s to 50 deg/s were considered and presented according to pseudorandom sequence. Ad hoc software suppressed catch-up saccades so that a pursuit index (PI) value was computed for each ramp taking into account only the smooth pursuit tracking modality. It was demonstrated that the relationship between V and PI could be described by the linear model PI = a + b * V. Pursuit index was proved to be influenced by the age of subject (decade factor in the analysis of variance), since an almost linear increase in b values yields a reduction of pursuit index values. The method was tested in 22 multiple sclerosis patients and an association was found between the occurrence of cerebellar signs and the reduction of a value.