Abstract
Infantile nystagmus (IN) describes a regular, repetitive movement of the eyes. A characteristic feature of each cycle of the IN eye movement waveform is a period in which the eyes are moving at minimal velocity. This so-called “foveation” period has long been considered the basis for the best vision in individuals with IN. In recent years, the technology for measuring eye movements has improved considerably, but there remains the challenge of calibrating the direction of gaze in tracking systems when the eyes are continuously moving. Identifying portions of the nystagmus waveform suitable for calibration typically involves time-consuming manual selection of the foveation periods from the eye trace. Without an accurate calibration, the exact parameters of the waveform cannot be determined. In this study, we present an automated method for segmenting IN waveforms with the purpose of determining the foveation positions to be used for calibration of an eye tracker. On average, the “point of regard” was found to be within 0.21° of that determined by hand-marking by an expert observer. This method enables rapid clinical quantification of waveforms and the possibility of gaze-contingent research paradigms being performed with this patient group.
Highlights
Infantile nystagmus (IN) describes a regular, repetitive movement of the eyes
Retinal imaging demonstrates that foveation periods usually coincide with the times at which the fovea is directed toward the object of regard (Felius et al, 2011), suggesting that foveations play an important role in visual perception in IN
The Bpoint of regard^—that is, the gaze location to be used for calibration—is the median gaze position from each of the samples selected by that method
Summary
Infantile nystagmus (IN) describes a regular, repetitive movement of the eyes. A characteristic feature of each cycle of the IN eye movement waveform is a period in which the eyes are moving at minimal velocity. We present an automated method for segmenting IN waveforms with the purpose of determining the foveation positions to be used for calibration of an eye tracker. The regular cycles of most adult IN waveforms contain periods during which the eye velocity (change in gaze angle over time) is significantly lower. These are known as Bfoveation^ periods, and their duration, velocity, and position variability across individuals are correlated with the underlying visual acuity (VA) deficit (Abadi & Worfolk, 1989; Bedell, White, & Abplanalp, 1989; Cesarelli, Bifulco, Loffredo, & Bracale, 2000). It is usually preferable to calibrate prior to starting a recording session, since this allows for live output of eye position coordinates (in degrees), as well as facilitating human–computer interaction and gazecontingent stimulus presentation
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