The effect of ageing on catch-up saccades during horizontal smooth pursuit eye movement

Old age affects gaze and postural coordination

Visual tracking of the surrounding environment is an important daily task, often executed simultaneously with the regulation of upright balance. Visual and postural coordination may be affected by aging which is associated with a decline in sensory and motor functions. The aim of the present study was to assess the effects of aging on the control of saccadic and smooth pursuit eye movements when standing on a moving surface. Nineteen young and 12 elderly subjects tracked a visual target presented as unpredictable smooth pursuit or saccadic displacements. Subjects were instructed to maintain gaze on target during quiet stance with or without yaw surface rotations. Elderly subjects followed both saccadic and pursuit targets with less accuracy than young subjects. Moreover, elderly subjects responded with longer time lags during saccadic target shifts and executed more catch-up saccades during smooth pursuits than younger subjects. Standing on a moving surface induced larger target-gaze errors. Catch-up saccades during pursuit occurred more frequently during surface perturbations. Our results suggest that visual tracking abilities decline with age and that postural challenge affects accuracy but not timing of gaze responses. Such declines observed with aging may result from multiple but minor sensory and motor deficits.

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.

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.

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.