Accuracy of eye position for saccades and smooth pursuit

Abstract

In this study, we address the question of whether a target is foveated during smooth pursuit. Specifically, we examine whether smooth pursuit eye movements land near the center-of-mass of the target, as is the case for saccades. To that end, we instructed eight untrained, healthy participants to follow moving targets, presented monocularly in a scanning laser ophthalmoscope. Stimuli moved either in a modified step-ramp (smooth pursuit), or made a single step (saccade), stepping 6° from the center. Targets were ring-shaped and either 0.6° or 1.7° in diameter. In an additional set of experiments, two participants collected more extensive data on smooth pursuit and saccades for a larger range of target sizes (0.6°, 1.7°, or 4.3°). During pursuit, eyes were rarely placed at target center, even when participants' fixational stability was taken into account. Furthermore, there was a clear tendency for distance from target center to increase with target size. This outcome was in contrast to saccades, where there was no effect of target size across participants. The difference in foveal placement between the two types of eye movements is consistent with their different purposes: closer inspection of the target for saccades versus maintenance of the target in the visual field for smooth pursuit.

Two-Dimensional Analysis of Smooth Pursuit Eye Movements Reveals Quantitative Deficits in Precision and Accuracy

“…A lower accuracy would suggest that the target was not being continuously foveated. Indeed, this would be consistent with the results of Shanidze et al,14 who found that small targets are not always foveated during pursuit. In typical observers, such eccentrically viewed targets have been shown to increase the variability of fixation eye movements,30 and may have had a similar impact on pursuit eye velocity.…”

“…Pursuit eye movements are likely to be no exception. For instance, in one of the few studies of the 2D nature of smooth pursuit, Shanidze et al14 sampled eye position as observers tracked a target that moved through the eight cardinal directions. The subsequent analyses quantified the proximity of eye position samples (60 Hz) to the pursuit target, and the results demonstrated that, for all pursuit directions, eye position varied not just along the target trajectory, but also orthogonal to it.…”

Image Stabilization in Central Vision Loss: The Horizontal Vestibulo-Ocular Reflex

“…Central vision loss results in deficits in visual functions such as acuity [4], contrast sensitivity [5], colour discrimination [6,7], insensitivity to flicker [8,9], delayed dark adaptation [10], shape perception [11], face recognition [12,13], stereopsis [14] and reading [15,16]. Patients adapt to the loss of central vision with the habitual use of an area of eccentric retina called the preferred retinal locus (PRL) as the new point of reference for the ocular motor system [17,18,19] Research on the ocular motor consequences of central vision loss has included fixation stability [20,21], saccades [22,23,24], smooth pursuit [25,26,27,28] and optokinetic nystagmus [29]. The vestibulo-ocular reflex (VOR) of patients with AMD and other low vision patients with various aetiologies has been explored along with other predictors of the functional success of telescopic spectacle use [30,31].…”

Automatic Measurements of Smooth Pursuit Eye Movements by Video-Oculography and Deep Learning-Based Object Detection

“…Strabismus is one of the eye movement disorders, and confirming of version eye movement, in which smooth pursuit eye movement (SPEM), 1-8 in nine directions is important to detect limitation of eye movement. 9-11 In most ophthalmology clinics, the examiner visually evaluates SPEM.…”