Torsional optokinetic nystagmus: normal response characteristics

Abstract

Background/aims: Few studies have investigated normal response characteristics of torsional optokinetic nystagmus (tOKN). The authors have investigated the effect of stimulus velocity and central/peripheral stimulation on tOKN. Methods: Torsional OKN was elicited using a sinusoidal grating rotating at velocities of 3˚/s to 1000˚/s in clockwise and anticlockwise directions. To investigate the effect of central stimulation, stimulus size was varied from 2.86˚to 50.8˚. An artificial scotoma placed over a 50.8˚stimulus was varied from 2.86˚to 43.2˚to investigate peripheral stimulation. Eight subjects participated in each experiment and torsional eye movements were recorded using video-oculography. The mean slow phase velocity (MSPV) and gain were calculated. Results: The maximum gain occurred in response to 8˚/s stimulation. The MSPV increased up to a stimulus velocity of 200˚/s achieving a maximum of 3˚/s in both directions. MSPV was linearly correlated with the log of stimulus velocity. The smallest field size, rotating at 40˚/s, evoked 10% of the gain elicited by the largest display. When the most peripheral stimulus was used, the gain was maintained at 50% of the gain evoked when the full display was used. Conclusions: A wide range of stimulus velocities can elicit tOKN and peripheral field stimulation contributes significantly to its response.

The initial torsional Ocular Following Response (tOFR) in humans: A response to the total motion energy in the stimulus?

“…We concentrated on the special case in which the monitor was positioned so that the axis of this rotation passed midway between the two eyes and the observer’s gaze was directed at the center of the display. This meant that, although the visual rotation was defined with respect to the head, each eye saw rotation about its optic axis, and many studies have shown that this induces torsional tracking of the two eyes in the direction of the seen rotation, often termed cycloversion (Cheung & Howard, 1991; Cheung, Money & Howard, 1995; Collewijn, van der Steen, Ferman & Jansen, 1985; Farooq, Gottlob, Benskin & Proudlock, 2008; Farooq, Proudlock & Gottlob, 2004; Houben, Goumans & van der Steen, 2006; Howard, Sun & Shen, 1994; Howard & Templeton, 1964; Ibbotson, Price, Das, Hietanen & Mustari, 2005; Kertesz & Jones, 1969; Lopez, Borel, Magnan & Lacour, 2005; Morrow & Sharpe, 1993; Seidman, Leigh & Thomas, 1992; Suzuki, Shinmei, Nara & Ifukube, 2000; Thilo, Probst, Bronstein, Ito & Gresty, 1999; van Rijn, van der Steen & Collewijn, 1992; 1994a; 1994b; Wade, Swanston, Howard, Ono & Shen, 1991; Washio, Suzuki, Sawa & Ohtsuka, 2005; Zupan & Merfeld, 2003). …”

“…When such roll-axis visual rotation is prolonged, the pattern of torsional eye movements resembles classical optokinetic nystagmus, with periods of smooth tracking interrupted by resetting saccades (e.g., Cheung & Howard, 1991; Cheung et al, 1995; Collewijn et al, 1985; Farooq et al, 2004; Howard et al, 1994; Ibbotson et al, 2005). Horizontal and vertical optokinetic nystagmus (hOKN and vOKN)—for which the adequate stimuli are also generally defined with respect to the head and involve visual rotations about the yaw and pitch axes, respectively—show a gradual buildup over time and—after the visual stimulus is extinguished—an appreciable afternystagmus (OKAN), two features that have been attributed to a central velocity-storage mechanism (Cohen, Matsuo & Raphan, 1977).…”

The Effect of Aging on Torsional Optokinetic Nystagmus

“…1 Stimulus velocities of 40°/s and 400°/s were considered suitable for use because these had previously elicited a good response that was easily differentiated from the normally occurring noise in the recording. 1 However, it is possible that tOKN responses are closer to threshold than horizontal and vertical OKN responses, making them more sensitive to aging. Another possibility is that tOKN responses are present in the elderly but fall below the level of system noise.…”

A new motor synergy that serves the needs of oculomotor and eye lid systems while keeping the downtime of vision minimal

“…One of these reflexes is the torsional optokinetic nystagmus (tOKN) (Farooq et al, 2004). It consists of a slow phase in which the eyes pursue the rotation of the visual stimulus in order to reduce the slip of its retinal image, followed by a torsional fast phase in the opposite direction.…”