Eye Torsion Research Articles

Static cervico-ocular reflex in healthy humans

Background Dynamic cervico- (COR) and vestibulo-ocular reflex (VOR) contribute to stabilise visual images in the retina. The gain in dynamic COR is small in healthy individuals but increases in patients with vestibular dysfunction. Conversely, static COR has not been directly observed in healthy individuals. Objectives To elucidate the presence of static COR and quantify it in normal individuals in the roll plane. Methods Eleven healthy participants were included in the study. Eye torsions were measured using video oculography to evaluate the static COR induced by lateral neck flexion during a head-upright-with-body-tilt position at 15°, 30°, and 45°. The ocular counterroll (OCR) was compared during whole-body and head tilts to assess the influence of static COR on OCR. Results Static COR was significantly observed as eye torsion in the direction opposite to the body tilt. The head tilt OCR was significantly smaller than the whole-body tilt OCR to the right side but not to the left side. Conclusion Static COR exists in healthy individuals and tends to show higher amplitude as neck flexion stimulation increases.

Real-time correction of image rotation with adaptive optics scanning light ophthalmoscopy.

Fixational eye motion includes typical translation and torsion. In the registration of images from adaptive optics scanning light ophthalmoscopy (AOSLO), image rotation due to eye torsion and/or head rotation is often ignored because (a) the amount of rotation is trivial compared to translation within a short duration of imaging or recording time and (b) computational cost increases substantially when the registration algorithm involves simultaneous detection of rotation and translation. However, it becomes critically important under cases such as long exposure, functional measurements, and precise motion tracking. We developed a fast method to detect and correct rotation from AOSLO images, together with the detection of strip-level motion translation. The computational cost for rotation detection and correction alone is about 5 ms/frame (512×512 pixels) on an nVidia GTX960M GPU. Image quality is compared with and without rotation correction from 10 healthy human subjects and 8 diseased eyes with a total of 180 videos. The results show that residual image motions between the reference images and the registered images with rotation correction are a fraction of those without rotation correction, and the ratio is 0.74-0.89 at the image center and 0.37-0.51 at the four corners of the images.

Ocular counter-roll is less affected in experienced versus novice space crew after long-duration spaceflight

Otoliths are the primary gravity sensors of the vestibular system and are responsible for the ocular counter-roll (OCR). This compensatory eye torsion ensures gaze stabilization and is sensitive to a head roll with respect to gravity and the Gravito-Inertial Acceleration vector during, e.g., centrifugation. To measure the effect of prolonged spaceflight on the otoliths, we quantified the OCR induced by off-axis centrifugation in a group of 27 cosmonauts in an upright position before and after their 6-month space mission to the International Space Station. We observed a significant decrease in OCR early postflight, larger for first-time compared to experienced flyers. We also found a significantly larger torsion for the inner eye, the eye closest to the rotation axis. Our results suggest that experienced cosmonauts have acquired the ability to adapt faster after G-transitions. These data provide a scientific basis for sending experienced cosmonauts on challenging missions that include multiple g-level transitions.

Non-invasive recognition of eye torsion through optical imaging of the iris pattern in ocular proton therapy

The introduction of non-invasive imaging techniques such as MRI imaging for treatment planning and optical eye tracking for in-room eye localization would obviate the requirement of clips implantation for many patients undergoing ocular proton therapy. This study specifically addresses the issue of torsional eye movement detection during patient positioning. Non-invasive detection of eye torsion is performed by measuring the iris pattern rotations using a beams eye view optical camera. When handling images of patients to be treated using proton therapy, a number of additional challenges are encountered, such as changing eye position, pupil dilatation and illumination. A method is proposed to address these extra challenges while also compensating for the effect of cornea distortion in eye torsion computation. The accuracy of the proposed algorithm was evaluated against corresponding measurement of eye torsion using the clips configuration measured on x-ray images. This study involves twenty patients who received ocular proton therapy at Paul Scherrer Institute and it is covered by ethical approval (EKNZ 2019-01987).

A Robust Method of Eye Torsion Measurement for Medical Applications

The detection of eye torsion is an important element for diagnosis of balance disorders, although it is rarely available in existing eye tracking systems. A novel method is proposed in this paper to provide robust measurement of torsional eye movements. A numerical approach is presented to estimate the iris boundary only according to the gaze direction, so the segmentation of the iris is more robust against occlusions and ambiguities. The perspective distortion of the iris pattern at eccentric eye positions is also corrected, benefiting from the transformation relation that is established for the iris estimation. The angle of the eye torsion is next measured on the unrolled iris patterns via a TM (Template Matching) technique. The principle of the proposed method is validated and its robustness in practice is assessed. A very low mean FPR (False Positive Rate) is reported (i.e., 3.3%) in a gaze test when testing on five participants with very different eye morphologies. The present method always gave correct measurement on the iris patterns with simulated eye torsions and rarely provided mistaken detections in the absence of eye torsion in practical conditions. Therefore, it shows a good potential to be further applied in medical applications.

V1 neurons encode the perceptual compensation of false torsion arising from Listing’s law

We try to deploy the retinal fovea to optimally scrutinize an object of interest by directing our eyes to it. The horizontal and vertical components of eye positions acquired by goal-directed saccades are determined by the object's location. However, the eccentric eye positions also involve a torsional component, which according to Donder's law is fully determined by the two-dimensional (2D) eye position acquired. According to von Helmholtz, knowledge of the amount of torsion provided by Listing's law, an extension of Donder's law, alleviates the perceptual interpretation of the image tilt that changes with 2D eye position, a view supported by psychophysical experiments he pioneered. We address the question of where and how Listing's law is implemented in the visual system and we show that neurons in monkey area V1 use knowledge of eye torsion to compensate the image tilt associated with specific eye positions as set by Listing's law.

Laboratory examinations for the vestibular system.

In the last decades, researchers suggested that clinical assessment of labyrinthine function in detail became easy thanks to video head impulse tests (VHITs), vestibular evoked myogenic potential test (VEMP) and video-oculography (VOG). It has been argued that they can replace electronystagmography, the caloric and rotatory chair tests. This review addresses the latest evaluations of these tests and the opportunities they offer, but also the limitations in clinical practice. The VHIT and suppression head impulse test (SHIMP) are under ideal circumstances able to accurately identify deficits of the VOR in 3D. However, in a relevant part of the patient population, pupil tracking is inaccurate, video-goggles slip and VOR quantification is problematic. The dissociation between the VHIT and caloric test suggests that these tests are complementary. A new 3D-VOG technique claims to quantify eye torsion better than before, opening multiple diagnostic possibilities. VEMPs remain difficult to standardize. Variability in normal cervical vestibular-evoked myogenic potential amplitude is large. VEMPs become smaller or absent with age, raising questions of whether there is a lower normal limit at all. Recent research shows that the labyrinth is directly stimulated in the MRI offering new opportunities for diagnostics and research. In clinical practice, the VHIT, SHIMP, VEMP and new 3D-VOG techniques improve diagnostic power. Unfortunately, technical issues or variability prevent reliable quantitative evaluation in a part of the regular patient population. The traditional caloric and rotatory chair test can still be considered as valuable complementary tests.

The somatogravic illusion during centrifugation: sex differences

Maintaining orientation in an environment with non-Earth gravity (1 g) is critical for an astronaut's operational performance. Such environments present a number of complexities for balance and motion. For example, when an astronaut tilts due to ascending or descending an inclined plane on the moon, the gravity vector will be tilted correctly, but the magnitude will be different from on earth. If this results in a mis-perceived tilt, then that may lead to postural and perceptual errors, such as mis-perceiving the orientation of oneself or the ground plane and corresponding errors in task judgment.

Attentional modulation of eye torsion responses.

Eye movements generally have both reflexive and voluntary aspects, but torsional eye movements are usually thought of as a reflexive response to image rotation around the line of sight (torsional OKN) or to head roll (torsional VOR). In this study we asked whether torsional responses could be modulated by attention in a case where two stimuli rotated independently, and whether attention would influence the latency of responses. The display consisted of rear-projected radial pinwheel gratings, with an inner annulus segment extending from the center to 22 degrees eccentricity, and an outer annulus segment extending from 22 degrees out to 45 degrees eccentricity. The two segments rotated around the center in independent random walks, stepping randomly 4 degrees clockwise or counterclockwise at 60 Hz. Subjects were asked to attend to one or the other while keeping fixation steady at the center of the display. To encourage attention on one or the other segment of the display, subjects were asked to move a joystick in synchrony with the back and forth rotations of one part of the image while ignoring the other. Eye torsion was recorded with the scleral search coil technique, sampled at 500 Hz. All four subjects showed roughly 50% stronger torsion responses to the attended compared to unattended segments. Latency varied from 100 to 150 msec across subjects and was unchanged by attention. These findings suggest that attention can influence eye movement responses that are not typically under voluntary control.

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

The purpose of blinks is to keep the eyes hydrated and to protect them. Blinks are rarely noticed by the subject as blink-induced alterations of visual input are blanked out without jeopardizing the perception of visual continuity, features blinks share with saccades. Although not perceived, the blink-induced disconnection from the visual environment leads to a loss of information. Therefore there is critical need to minimize it. Here we demonstrate evidence for a new type of eye movement serving a distinct oculomotor demand, namely the resetting of eye torsion, likewise inevitably causing a loss of visual information. By integrating this eye movement into blinks, the inevitable down times of vision associated with each of the two behaviors are synchronized and the overall downtime minimized.

Psychophysical observation of head tilt vestibulo-ocular reflex

Purpose: The vestibulo-ocular reflex eye movements can be observed psychophysically. When we roll, pitch, or yaw our head, we perceive the movements of texture due to the reflex. The eye torsion reflex by head tilt is of most interest, since it cannot be voluntarily controlled and manifest the clear reflexes. Methods: Under the “world” conditions, the stimulus was fixed to the environment. Under the “head” conditions, the stimulus was presented by a head mounted display. The images had simple textures such as some horizontal lines depicted with low contrast grays or equiluminant colors. The lines and the background alternated with their colors, flickering at 10–20 Hz. The normal subjects tilted his head as observing the image. Results: Under the “world” conditions, with the clockwise tilt from left to right lateral in 0.5 second, the subjects first perceived the salient clockwise rotation of the texture then perceived the rather slow counterclockwise rotation that soon died away. When the head was tilted slowly such as in 2 seconds from one lateral to the other, the subjects perceived the consecutive rotations of the texture and observed no counter rotation. The images in the head mounted display gave the opposite directional motion perceptions. The clockwise tilt caused first the counterclockwise and then the clockwise rotations. Though, the motions were rather less salient under the “head” conditions, they were qualitatively similar to that of the “world” except the directions. Discussions: The motion under the “world” would be derived from the retinal slip of the image caused by the head tilt and the slightly delayed compensating reflex eye torsion followed by the eye returning to the primary orientation. Under the “head” conditions the retinal slips were caused only by the reflex torsions. The slips were in the opposite directions to that of the “world”. These slips were consistent to the observations.

Perception of tilt and ocular torsion of vestibular patients during eccentric rotation

Four patients following unilateral vestibular loss and four patients complaining of otolith-dependent vertigo were tested during eccentric yaw rotation generating 1 x g centripetal acceleration directed along the interaural axis. Perception of body tilt in roll and in pitch was recorded in darkness using a somatosensory plate that the subjects maintained parallel to the perceived horizon. Ocular torsion was recorded by a video camera. Unilateral vestibular-defective patients underestimated the magnitude of the roll tilt and had a smaller torsion when the centrifugal force was towards the operated ear compared to the intact ear and healthy subjects. Patients with otolithic-dependent vertigo overestimated the magnitude of roll tilt in both directions of eccentric rotation relative to healthy subjects, and their ocular torsion was smaller than in healthy subjects. Eccentric rotation is a promising tool for the evaluation of vestibular dysfunction in patients. Eye torsion and perception of tilt during this stimulation are objective and subjective measurements, which could be used to determine alterations in spatial processing in the CNS.

Reacción ocular de inclinación en infarto talámico

Ocular tilt reaction (OTR) includes skew deviation, eye torsion and head tilt. It is usually accompanied by a tilt in the subjective visual vertical. OTR seems to reflect an otolithic dysfunction. This case report shows an OTR of central origin as a result of simultaneous paramedial thalamic and mesencephalon rostral infarcts.

Ocular tilt reaction in thalamic infarct

Ocular tilt reaction (OTR) includes skew deviation, eye torsion, and head tilt. It is usually accompanied by a tilt in the subjective visual vertical. OTR seems to reflect an otolithic dysfunction. This case report shows an OTR of central origin as a result of simultaneous paramedial thalamic and mesencephalon rostral infarcts.

On the relation between ocular torsion and visual perception of line orientation

A recent study by Poljac et al. [Poljac, E., Lankheet, M. J. M., & van den Berg, A. (2005). Perceptual compensation for eye torsion. Vision Research, 45(4), 485–496] concluded that there was complete perceptual compensation for ocular torsion, although they did not directly measure ocular torsion. Using a similar eccentric-gaze paradigm to induce changes in torsion, which were directly measured, we found inconsistent torsional eye movements at eccentric fixation, and also failed to detect a significant relationship between ocular torsion and the perception of line orientation. We then used a stimulus known to induce large changes in ocular torsion: on-centre yaw rotation. This stimulus induced a consistent change in the torsional position of the eye which positively correlated to subjects’ visual perception of horizontal.

The Effect of Acute Superior Oblique Palsy on Torsional Optokinetic Nystagmus in Monkeys

To investigate the effects of acquired superior oblique palsy (SOP) and corrective strabismus surgery on torsional optokinetic nystagmus (tOKN) in monkeys. The trochlear nerve was severed intracranially in two rhesus monkeys (M1 and M2). For each monkey, more than 4 months after the SOP, the ipsilateral inferior oblique muscle was denervated and extirpated. For M2, 4 months later, the contralateral inferior rectus muscle was recessed by 2 mm. tOKN was elicited during monocular viewing of a rotating stimulus that was rear projected onto a screen 43.5 cm in front of the animal. Angular rotation of the stimulus about the center was 40 deg/s clockwise or counterclockwise. The main findings after trochlear nerve sectioning were (1) the amplitude and peak velocity of torsional quick and slow phases of the paretic eye was less than that in the normal eye for both intorsion and extorsion, and (2) the vertical motion of the paretic eye increased during both torsional slow and quick phases. After corrective inferior oblique surgery, both of these effects were even greater. Acquired SOP and corrective inferior oblique-weakening surgery create characteristic patterns of change in tOKN that reflect alterations in the dynamic properties of the extraocular muscles involved in eye torsion. tOKN also provides information complementary to that provided by the traditional Bielschowsky head-tilt test and potentially can help distinguish among different causes of vertical ocular misalignment.

Analyzing head roll and eye torsion by means of offline image processing

Ocular torsion is a key problem in the understanding of many visual perceptual effects. However, since it is difficult to record, its integration with other sensorimotor signals is still poorly understood. Unfortunately, eyetracker systems are generally not dedicated to the monitoring of eye torsion. In addition, the classical methods used with video-based systems present some limits in the accuracy of torsion calculation. These limits are especially related to the detection of pupil center and the effects of pupil size changes. This article aims at (1) proposing a solution to analyze ocular torsion together with head roll using EyeLink II or similar equipment, (2) reviewing and adapting classical polar cross-correlation methods in order to improve the accuracy of torsion measurement, (3) providing a lower-cost method compared with the existing ones. Video sequences issued from the EyeLink II host computer monitor were recorded by means of a second computer equipped with a video acquisition card and converted into image sequences. Images were analyzed with algorithms of pupil center detection (median-based algorithm), torsion analysis (adapted polar cross-correlation method which takes into account pupil size variations) and marker tracking (head roll analysis). This method was tested on virtual eye images. Results are discussed with respect to other algorithms found in the literature.

Dynamic pitch rotation affects eye torsion

Conclusion. Most of the subjects studied had eye torsion responses to pitch, although the direction of torsion varied between subjects. Opposite responses may be the result of individual variation in anatomical or physiological vector orientations of hair cells in the anterior or posterior utricle or in the saccule. Objective. This study aimed to determine whether systematic changes in eye torsion occur when subjects are rotated in forward and backward pitch. Materials and methods. Twenty-one normal subjects were seated in a dual axis human rotator, positioned so that the interaural axis was aligned with the axis of pitch rotation. Fixation LED suppressed vertical or horizontal eye movement. Recordings were carried out in darkness apart from the fixation LED, using a three-dimensional eye tracker based on CMOS image sensors. Subjects were twice tilted from upright to 90° occiput down, then forward to 45° face down. Results. Most subjects had eye torsion changes in response to pitch, with mean amplitudes of approximately 2° to 90° backward tilt and 1° to 45° forward tilt. Ten subjects had clockwise torsion to backward pitch and counterclockwise to forward pitch; six subjects had the opposite responses. Statistical testing of the distributions of the regression slopes between these two groups were significant (p<0.001). Five subjects had unclear responses.

Kinematics of Vertical Saccades during the Yaw Vestibulo-ocular Reflex in Humans

Listing's law (LL) constrains the rotational axes of saccades and pursuit eye movements to Listing's plane (LP). In the velocity domain, LL is ordinarily equivalent to a tilt in the ocular velocity axis equal to half the change in eye position, giving a tilt angle ratio (TAR) of 0.5. This study was undertaken to investigate vertical saccade behavior after the yaw vestibulo-ocular reflex (VOR) had driven eye torsion out of LP, an initial condition causing the position and velocity domain formulations of LL to differ. Binocular eye and head motions were recorded with magnetic search coils in eight humans. With the head immobile, LP was determined for each eye, and mean TAR was 0.50 +/- 0.07 (mean +/- SD) for horizontal and 0.45 +/- 0.11 for vertical saccades. The VOR was evoked by transient, whole-body yaw at 2800 deg/s2 peak acceleration, capable of evoking large, uninterrupted VOR slow phases. Before rotation, subjects viewed a target at eye level, 20 degrees up, or 20 degrees down. In two thirds of the trials, the target moved upward or downward at systematically varying times, triggering a vertical saccade during the horizontal VOR slow phase. Because the head rotation axis was generally misaligned with LP, the eye averaged 3.6 degrees out of LP at vertical saccade onset. During the saccade, eye position continued to depart LP by an average 0.8 degrees. The horizontal TAR at saccade onset was 0.29 +/- 0.07. At peak saccade velocity 35 +/- 3 ms later, the vertical TAR was 0.45 +/- 0.07, statistically similar to that of head fixed saccades. Saccades did not return to LP. Although they did not observe the position domain formulation of LL, vertical saccades, during the VOR, observed the half-angle velocity domain formulation of LL.

Perceptual compensation for eye torsion

To correctly perceive visual directions relative to the head, one needs to compensate for the eye’s orientation in the head. In this study we focus on compensation for the eye’s torsion regarding objects that contain the line of sight and objects that do not pass through the fixation point. Subjects judged the location of flashed probe points relative to their binocular plane of regard, the mid-sagittal or the transverse plane of the head, while fixating straight ahead, right upward, or right downward at 30 cm distance, to evoke eye torsion according to Listing’s law. In addition, we investigated the effects of head-tilt and monocular versus binocular viewing. Flashed probe points were correctly localized in the plane of regard irrespective of eccentric viewing, head-tilt, and monocular or binocular vision in nearly all subjects and conditions. Thus, eye torsion that varied by ±9° across these different conditions was in general compensated for. However, the position of probes relative to the midsagittal or the transverse plane, both true head-fixed planes, was misjudged. We conclude that judgment of the orientation of the plane of regard, a plane that contains the line of sight, is veridical, indicating accurate compensation for actual eye torsion. However, when judgment has to be made of a head-fixed plane that is offset with respect to the line of sight, eye torsion that accompanies that eye orientation appears not to be taken into account correctly.