Electrooculography
Encyclopedia
Electrooculography is a technique for measuring the resting potential
of the retina
. The resulting signal is called the electrooculogram. The main applications are in ophthalmological
diagnosis
and in recording eye movements. Unlike the electroretinogram
, the EOG does not represent the response to individual visual stimuli.
Eye movement measurements: Usually, pairs of electrodes are placed either above and below the eye or to the left and right of the eye. If the eye is moved from the center position towards one electrode, this electrode "sees" the positive side of the retina and the opposite electrode "sees" the negative side of the retina. Consequently, a potential difference occurs between the electrodes. Assuming that the resting potential is constant, the recorded potential is a measure for the eye position.
1. Left gaze: the cornea approaches the electrode near the outer canthus of the left eye, resulting in a positive-going change in the potential difference recorded from it.
2. Right gaze: the cornea approaches the electrode near the inner canthus of the left eye, resulting in a positive-going change in the potential difference recorded from it (A, an AC/DC amplifier).
, the resting potential decreases slightly and reaches a minimum ("dark trough") after several minutes. When the light is switched on, a substantial increase of the resting potential occurs ("light peak"), which drops off after a few minutes when the retina adapts to the light. The ratio of the voltages (i.e. light peak divided by dark trough) is known as the Arden ratio. In practice, the measurement is similar to the eye movement recordings (see above). The patient is asked to switch the eye position repeatedly between two points (usually to the left and right of the center). Since these positions are constant, a change in the recorded potential originates from a change in the resting potential.
and Jerome Chen, the visual effects supervisor in the movie Beowulf
, to enhance the performance capture by correctly animating the eye movements of the actors. The result was an improvement over the technique used for the film The Polar Express
.
Electrooculography was used in the Neural Impulse Actuator
, a product of the now defunct company OCZ Technology
. This device helps gamers to increase their playing speed.
Resting potential
The relatively static membrane potential of quiescent cells is called the resting membrane potential , as opposed to the specific dynamic electrochemical phenomena called action potential and graded membrane potential....
of the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
. The resulting signal is called the electrooculogram. The main applications are in ophthalmological
Ophthalmology
Ophthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems...
diagnosis
Diagnosis
Diagnosis is the identification of the nature and cause of anything. Diagnosis is used in many different disciplines with variations in the use of logics, analytics, and experience to determine the cause and effect relationships...
and in recording eye movements. Unlike the electroretinogram
Electroretinography
Electroretinography measures the electrical responses of various cell types in the retina, including the photoreceptors , inner retinal cells , and the ganglion cells. Electrodes are usually placed on the cornea and the skin near the eye, although it is possible to record the ERG from skin electrodes...
, the EOG does not represent the response to individual visual stimuli.
Eye movement measurements: Usually, pairs of electrodes are placed either above and below the eye or to the left and right of the eye. If the eye is moved from the center position towards one electrode, this electrode "sees" the positive side of the retina and the opposite electrode "sees" the negative side of the retina. Consequently, a potential difference occurs between the electrodes. Assuming that the resting potential is constant, the recorded potential is a measure for the eye position.
Principle
The eye acts as a dipole in which the anterior pole is positive and the posterior pole is negative.1. Left gaze: the cornea approaches the electrode near the outer canthus of the left eye, resulting in a positive-going change in the potential difference recorded from it.
2. Right gaze: the cornea approaches the electrode near the inner canthus of the left eye, resulting in a positive-going change in the potential difference recorded from it (A, an AC/DC amplifier).
Ophthalmological diagnosis
The EOG is used to assess the function of the pigment epithelium. During dark adaptationAdaptation (eye)
In ocular physiology, adaptation is the ability of the eye to adjust to various levels of darkness and light.-Efficacy:The human eye can function from very dark to very bright levels of light; its sensing capabilities reach across nine orders of magnitude. This means that the brightest and the...
, the resting potential decreases slightly and reaches a minimum ("dark trough") after several minutes. When the light is switched on, a substantial increase of the resting potential occurs ("light peak"), which drops off after a few minutes when the retina adapts to the light. The ratio of the voltages (i.e. light peak divided by dark trough) is known as the Arden ratio. In practice, the measurement is similar to the eye movement recordings (see above). The patient is asked to switch the eye position repeatedly between two points (usually to the left and right of the center). Since these positions are constant, a change in the recorded potential originates from a change in the resting potential.
Application in Entertainment
Electrooculography was used by Robert ZemeckisRobert Zemeckis
Robert Lee Zemeckis is an American film director, producer and screenwriter. Zemeckis first came to public attention in the 1980s as the director of the comedic time-travel Back to the Future film series, as well as the Academy Award-winning live-action/animation epic Who Framed Roger Rabbit ,...
and Jerome Chen, the visual effects supervisor in the movie Beowulf
Beowulf (2007 film)
Beowulf is a 2007 American animated fantasy film written by Neil Gaiman and Roger Avary inspired by the Old English epic poem of the same name. Directed by Robert Zemeckis, the film was created through a motion capture process similar to the technique he used in The Polar Express...
, to enhance the performance capture by correctly animating the eye movements of the actors. The result was an improvement over the technique used for the film The Polar Express
The Polar Express (film)
The Polar Express is a 2004 motion capture computer-animated film based on the children's book of the same title by Chris Van Allsburg. Written, produced, and directed by Robert Zemeckis, the human characters in the film were animated using live action performance capture technique, with the...
.
Electrooculography was used in the Neural Impulse Actuator
Neural Impulse Actuator
The Neural Impulse Actuator is a brain–computer interface device developed by OCZ Technology. BCI devices attempt to move away from the classic input devices like keyboard and mouse and instead read electrical activity from the head, preferably the EEG...
, a product of the now defunct company OCZ Technology
OCZ Technology
OCZ Technology is a manufacturer of computer hardware based in San Jose, California, USA. Since entering the memory market in 2002, OCZ has targeted its products primarily at the computer hardware enthusiast market, first producing performance DDR RAM, Video Cards, USB drives, and various Cooling...
. This device helps gamers to increase their playing speed.
See also
- International Society for Clinical Electrophysiology of VisionInternational Society for Clinical Electrophysiology of VisionThe International Society for Clinical Electrophysiology of Vision is an association that promotes research and applications of electrophysiological methods in clinical diagnosis of ophthalmological diseases...
- Optokinetic drumOptokinetic drumAn optokinetic drum is a rotating instrument to test vision in which individuals are seated facing the wall of the drum. The interior surface of the drum is normally striped; thus, as the drum rotates, the subject's eyes are subject to a moving visual field while the subject remains stationary. ...
- Orthoptist
- NystagmusNystagmusNystagmus is a condition of involuntary eye movement, acquired in infancy or later in life, that may result in reduced or limited vision.There are two key forms of Nystagmus: pathological and physiological, with variations within each type. Nystagmus may be caused by congenital disorders,...