Video-oculography System Research Articles

Saccadic eye movements in children: a developmental study

To our knowledge, there are no studies exploring the development of voluntary and reflexive saccades in children using different types of paradigms to investigate horizontal saccades. In the present study, we examined the development of horizontal saccades in children aged 6-15 years. Binocular eye movements were recorded using an infrared video-oculography system (mobileEBT(®), e(ye)BRAIN) in seventy-two children (aged 6-15). Several paradigms were used to stimulate reflexive and voluntary horizontal saccades: gap, step and overlap paradigms. Horizontal anti-saccades were also examined. In all paradigms, the latency of saccades decreased with the age of children and it did not depend on the direction of the saccades (left/right); the error rate in the anti-saccade task decreased with age; the gain of horizontal saccades improved with age; the peak velocity of horizontal saccades was stable throughout childhood. We conclude that saccadic performances are influenced by age and cortical circuits responsible for the preparation of reflexive or voluntary saccades are completed at 12 years old. These data could be used as reference values for further studies dealing with pathologic development.

Study of Polynomial Mapping Functions in Video-Oculography Eye Trackers

Gaze-tracking data have been used successfully in the design of new input devices and as an observational technique in usability studies. Polynomial-based Video-Oculography (VOG) systems are one of the most attractive gaze estimation methods thanks to their simplicity and ease of implementation. Although the functionality of these systems is generally acceptable, there has been no thorough comparative study to date of how the mapping equations affect the final system response. After developing a taxonomic classification of calibration functions, we examined over 400,000 models and evaluated the validity of several conventional assumptions. Our rigorous experimental procedure enabled us to optimize the calibration process for a real VOG gaze-tracking system and halve the calibration time while avoiding a detrimental effect on the accuracy or tolerance to head movement. Finally, a geometry-based method is implemented and tested. The results and performance is compared with those obtained by the general purpose expressions.

A Pupil Location Method for WIFI-based Video-oculography System

Video-oculography (VOG) is one of eye movement measurement methods. A key problem of VOG is to accurately estimate the pupil center. Then a pupil location method based on morphology and Canny algorithm was proposed for a WIFI-based VOG system which was developed our latest work. Moreover, a healthy volunteer was introduced to do sinusoidal tracking test to evaluate the pupil location method. Experimental results showed that the method could well trace eye movement and meet the anticipated results with stimulation.

Signal Analysis of Three-dimensional Nystagmus for Otoneurological Investigations

Three-dimensional signal analysis can be applied to eye movements called nystagmus in order to study otoneurological patients suffering from vertigo and other balance problems. We developed an analysis and modeling algorithm for three-dimensional nystagmus measured by a video-oculography system. We were also interested in verifying an otoneurological hands-on convention called Ewald's first law in a strict physiological sense in vestibular patients. We recorded nystagmus from 42 patients all suffering from vertigo or dizziness. The underlying pathology was unilateral in 39 patients, bilateral in one patient, and central in two patients. Video-oculography was used to record three-dimensional nystagmus to separately produce horizontal, vertical, and torsional signals for each eye. On the basis of signal analysis techniques and straightforward vector calculus, we were able to recognize slow phases of nystagmus to compute their angular velocities to estimate from which part of the inner ear the disorder originated. We found that for all 42 patients the plane of one of the two horizontal semicircular canals was the closest. We were able to quantitatively estimate the influence of different semicircular canals, and, despite the pathology, horizontal canals seemed to be predominant in driving the nystagmus. The signal analysis and modeling algorithm developed is effective in studying otoneurological problems registered with nystagmus and opens new insights in three-dimensional nystagmography. Our results strongly support Ewald's first law.

Impulsive Testing of Semicircular‐Canal Function Using Video‐oculography

The head impulse test (HIT) is a safe, quick way of assessing horizontal semicircular-canal function in patients with peripheral vestibular loss. At the bedside, the clinician identifies "overt" catch-up saccades back to the target after brisk passive head rotation as an indirect sign of canal paresis. However, saccades during head rotation ("covert" saccades) may not be detectable by the naked eye, and so lead to incorrect diagnosis. Up to now, the scleral search coil technique has been the standard for HIT measurement, but that technique is not practical for routine diagnostic use. A new lightweight, nonslip, high-speed video-oculography system (vHIT) that measures eye velocity during horizontal head impulses has been developed. This system is easy to use in a clinical setting, provides an objective measure of the vestibulo-ocular reflex (VOR), and detects both overt and covert catch-up saccades in patients with vestibular loss.

Drift of Visually Induced Optostatic Torsion

Purpose: Compensatory ocular torsion has been found in response to static tilted visual stimuli. The purpose was to investigate if visually induced ocular torsion is maintained during continuous stimulation and to reinvestigate the effect of stimuli tilt angle. Methods: Eye movements were recorded in 19 healthy individuals using a 3-D video oculography system. One visual stimulus was used in the tests, a photographic image of a city scene with spatial clues relevant for body posture. The scenes were tilted counterclockwise around a central pivot point from 0 to 15 degrees (test A), from 0 to 30 degrees (test B), and from 0 to 45 degrees (test C). Each tilted stimulus position was held static for 4 min, 40 sec. Results: A compensatory torsional response was found in all subjects and test conditions. No significant difference was found between the different stimuli tilt angles. The torsional response was not maintained but drifted back towards the reference position. Conclusions: Visually induced ocular torsion in response to a static tilted scene is not maintained, but drifts back towards the initial reference position. Higher cognitive functions such as imagination and attention certainly have an influence on the outcome.

Minimization of influence by the drooping eyelid in extracting pupil center for eye tracking systems

Precise pupil center detection is an important factor for gaze tracking in video-oculography (VOG) systems. Existing methods perform well to extract the features when the area of pupil in eye image is clear, whereas, interferences, such as eyelashes, corneal reflection etc., will lead to a low success rate. One main reason is the closure of eyelids. In this paper, a systemic 3D transformation algorithm is proposed to accurately ascertain the pupil center, in spite of the complicating factors mentioned above. Experiments show the good performance of our method. And the pupil center could be extracted accurately, even though only 25% of the pupil is visible.

The effect of alcohol ingestion on ocular counterrolling

Nineteen normal subjects underwent two naso-occipital rotations to 90 degrees right and left ear down in our standard ocular counterrolling (OCR) protocol. Both eyes were videotaped. Following two rotations, subjects drank 90 ml vodka in 180 ml orange juice; and in about 20 min, when blood alcohol levels reached 0.04-0.09%, the protocol was repeated. An SMI videooculography system provided measurements. Results showed that amplitude of OCR was significantly decreased after alcohol ingestion; smoothness was significantly increased after alcohol, similar to alcohol's effect on essential tremor. Although disconjugacy was not significantly different in the two conditions when the entire trials were examined, the latter portions of the post-alcohol trials did show significant disconjugacy, similar to earlier findings in vestibular-defective patients whose OCR deficits were apparent only in the final segments of the rotation trials. We postulate the results are due to alcohol's action on cerebellar GABAergic Purkinje cells projecting to vestibular nuclei.

眼球運動三次元回転軸解析の臨床応用

We developed a new video-oculography (VOG) system that can facilitate analysis of the axis angle, rotation vector or quaternions of eye movements. The axis angle, rotation vector, and quaternions measure a single rotation from a chosen reference position to the current eye position. Using the axis angle, rotation vector, or quaternions, we can calculate the axis around which the eye rotates and the angular velocity around the axis. In this review, we show how we utilize the analysis of eye rotational axis and eye velocity around the axis in clinical applications. By calculating the axis of positional nystagmus in benign paroxysmal positional vertigo (BPPV) patients, we can identify the affected lesion in the semicircular canals. Posterior semicircular canal (PSCC) type of BPPV causes positional nystagmus in which the rotational axis is perpendicular to the plane of the PSCC or pure torsional axis. Horizontal semicircular canal (HSCC) type of BPPV (H-BPPV) causes positional nystagmus in which the rotational axis is perpendicular to the plane of the HSCC. A dramatic change in the eye angular velocity and time constant of nystagmus is seen at the transitional period when cupulolithiasis changes to canalolithiasis in a patient with H-BPPV. Anterior semicircular canal (ASCC) type of BPPV causes positional nystagmus in which the eye rotational axis is perpendicular to the plane of the ASCC. BPPV due to the simultaneous involvement of both horizontal and posterior semicircular canals has two rotational axes; first, it is perpendicular to the plane of the PSCC, then, it is perpendicular to the plane of the HSCC. By calculating the eye angular velocity around the axis, we can show that the gain of the vestibulo-ocular reflex around the eye rotational axis can be calculated both when HSCCs are mainly stimulated and when vertical semicircular canals are mainly stimulated.

Visual spatial clues enhance ocular torsion response during visual tilt

Ocular torsion in response to a static tilt of a visual stimulus has been, and still remains in doubt. Furthermore, the possible underlying mechanism is not well understood. The authors' hypothesize that if the torsional response is related to the vestibular otolith system, then a visual stimulus with spatial clues important for maintaining body posture will induce a larger torsional response as compared to a stimulus lacking spatial information. Eye movements were recorded objectively in 15 healthy individuals using a 3D video oculography system. Three visual stimuli were used. In two tests, an identical photographic image of a city scene with spatial clues relevant for body posture were used, with the only difference being a square periphery in one stimulus (test 1) and a circular periphery in the other (test 2). The third stimulus (test 3) consisted of yellow rectangles on a black background with no natural spatial information. The scenes were tilted in 15 degrees steps from 0 degrees to 45 degrees in CCW and CW direction, and each position were held static for 15 s. All visual scene tilts induced a compensatory torsional response, which increased with stimuli angle. The stimuli with spatial clues induced more torsion compared to the stimulus without spatial clues. No difference was found when analysing the peripheral contour effect or direction of stimulus tilt. The present results support the hypothesis of an origin in the otolith system for the torsional response found to a static tilted visual scene.

Ｖｉｄｅｏ‐ｏｃｕｌｏｇｒａｐｈｙ（ＶＯＧ）―眼球運動の三次元解析―

There are two methods for measurement of eye position in three dimensions. One is the scleral search coil technique and the other is video-oculography (VOG). Although the VOG system is not as accurate as the scleral search coil system in the ability of time and space resolution, it is suitable for clinical use. There are two types of VOG system: One for analysis using Fick coordinates, and the other for analysis using axis angle, rotation vector and quaternions. Fick coordinate analysis measures three consecutive rotations about the horizontal, vertical, and torsional eye-fixed axes. Axis angle, rotation vector and quaternions measure single axis rotation from a chosen reference position to the current eye position. The system for analyzing by Fick coordinates utilizes the movement of the center of the pupil in order to calculate horizontal and vertical eye movement. In order to calculate the torsional component, the system uses the movement of an iris freckle or iris pattern. The system for analyzing axis angle, rotation vector and quaternions reconstructs the three-dimensional coordinates of the center of the pupil and an iris freckle in space. From these movements in space, the system calculates axis angle, rotation vector and quarternions. In this review, such two type of VOG systems are introduced, and the advantages and disadvantages of both types are discussed.