Eye Movements

Abstract

A description of eye movements is presented in this chapter. In addition, models of the saccadic system and smooth pursuit system are also presented. Five different types of eye movements exist: saccades, smooth pursuit, vestibular ocular eye movements, optokinetic eye movements, and vergence eye movements. Saccades are a fast eye movement used to acquire a target by placing the image of the target on the fovea. Smooth pursuit is a slow eye movement used to track a target as it moves by keeping the target on the fovea. The vestibular ocular movement is used to keep the eyes on a target during brief head movements. The optokinetic eye movement is a combination of saccadic and slow eye movements that keeps a full‐field image stable on the retina during sustained head rotation. Each of these movements is a conjugate eye movement, that is, movements of both eyes together driven by a common neural source. A vergence movement is a nonconjugate eye movement allowing the eyes to track targets as they come closer or move farther away. The smooth pursuit system allows tracking of a slow‐moving target to maintain its position on the fovea. Models of the smooth pursuit have been developed using systems control theory, all involving a negative feedback control system that includes a time delay, controller, and plant in the forward loop with unity feedback. The oculomotor plant and saccade generator are the basic elements of the saccadic system. The oculomotor plant consists of three muscle pairs and the eyeball. The control of saccades is initiated by the superior colliculus (SC) and terminated by the cerebellar fastigial nucleus (FN), and involves a complex neural circuit in the mid brain. Both of these control models are for horizontal eye movements only.

An Affordable Method for Evaluation of Ataxic Disorders Based on Electrooculography

“…The typical EOG amplitude ranges from 0.05–3.5 mV in humans, but this varies with the environmental conditions and in cases of any eye disease [36]. The bandwidth is between dc and 50 Hz, but the frequencies of interest are in the range of 0.1–40 Hz [37].…”

“…The peak amplitude depends on the angular stroke of the saccade. Fixations are the state during which the gaze is focused on a specific location [32,33,34,37]. During fixations on an object in the environment, it is possible to discover micromovements of an involuntary nature (drifts and flicks) that have amplitude around 1°.…”

Development of a Computer Writing System Based on EOG

“…With the movement of the eyeball, an electric field is generated, which can then be measured. The EOG amplitude varies from 50 to 3500 µV and its frequency ranges from DC to 50 Hz [ 34 , 35 ]. However, an EOG signal is not deterministic.…”

A Simple Gaze Tracker for Computer Operation by the Disabled in Education

“…Such areas as visual perception, reading technique determination, instrument panel layout design and driving analysis have all benefi ted from eye movement recordings. Eye tracking has been implemented using a variety of technologies, ranging from a small coil affi xed to the eye ball (using electromagnetic (EM) induction) to optic devices (using cameras to record sequences of images of the iris) and complete image processing of the head of the person (ENDERLE, 2006). Another technique for eye tracking mostly used in clinical settings processes the electrical signal detected on the skin by the eyes: the electrooculogram EOG.…”

“…Although the linearity of the EOG with eye position has been established, little was done (ENDERLE, 2006, STIEFELHAGEN, 1997 to use it for purposes other than basic research or diagnostics. Our aim (GONZÁLEZ; GAR-CÍA; TULLI, 2005) was to record the eye position with a device that could be worn with minimal discomfort for a long time during the day.…”