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Electrooculography
 

Electrooculography

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    Electrooculography Electrooculography Presentation Transcript

    • ELECTROOCULOGRAPHY .
    • INTRODUCTION  Eyes are our window to this large universe.  Advancements in the field of biomedical electronics and in the field of electronics and communication system have changed the perception of eye.  It is estimated 150, 00 severely disabled persons able to control only the muscles of their eyes without any problem.
    • HISTORY  Emil du Bois-Reymond (1848) observed that the cornea of the eye is electrically positive relative to the back of the eye.  Elwin Marg named the electrooculogram in 1951 and Geoffrey Arden in 1962 developed the first clinical application.
    • ELECTROOCULOGRAPHY  It is a technique for measuring the resting and action potential of the retina.  Four to five electrodes, and the amplifiers and filters are required  Usually, pairs of electrodes are placed either above and below the eye or to the left and right of the eye.
    • ANATOMY OF THE EYE
    • THE ELECTROOCULOGRAM  The ElectroOculoGram (EOG) is the electrical signal produced by the potential difference between the retina and the cornea of the eye.  This difference is due to the large presence of electrically active nerves in the retina compared to the front of the eye.  Eye movement will respectively generates voltage up to 16µV and 14µV per 1° in horizontal and vertical way.
    • EYE MOVEMENTS Four types of eye movements are  Saccades  Smooth pursuit movements  Vergence movements  Vestibulo-ocular movements
    • EOG Detection  Four to five electrodes are reqd.  The electrodes act as transducers.  Two electrodes are placed on the outer side of the eye.  Another pair above and below the eye  And a reference electrode
    • …contd  Placement of electrodes  Horizontal  Reference  Vertical
    • EOG Signals  HEOG Signals: Obtained from horizontal eye movements  Eye movement: from centre to left: +ve voltage spike from center to right:-ve voltage spike  VEOG Signals: Obtained from vertical eye movements  Eye movement: from centre to top: +ve voltage spike from centre to bottom: -ve voltage spike  Blink Signals: Obtained due to blinking of eyes  Voluntary Blink Signals  Involuntary Blink Signals
    • …contd
    • EOG Electrodes Characteristics required:  Stable electrode potential  Equal electrode potentials  Equal electrode resistances  Low electrode resistance
    • …contd  The two type of electrodes used are:  Ag-AgCl Electrode:  It is a type of reference electrode.  The electrode is a silver wire that is coated with a thin layer of silver chloride.  A porous plug on one end allows contact between the field environment with the silver chloride electrolyte.  They are inexpensive to manufacture, are simple construction and have stable potential.  Metal disk electrode:  They are generally made of high purity tin, silver, gold or even surgical steel  Application area is near the eye region  Diameter range is 4-10mm
    • EOG Signal Filtering and Acquisition System
    • APPLICATIONS  Electrooculographic guidance of a wheelchair using eye movements.  A portable wireless eye movement-controlled Human-Computer Interface for the Disabled.
    • Electrooculographic Guidance Of A Wheelchair Using Eye Movements
    • Eye Movement Controlled Human-Computer Interface  Human Computer Interface(HCI) is a device used by the disabled who have motor paralysis and have difficulty in conveying their intentions.  The only muscle they can control are the eye muscles.  It is a real time communication system based on EOG signal  It has four major parts  Five electrodes  A two channel amplifier  A laptop (or a microprocessor)  A ZigBee wireless module
    • ….contd
    • ADVANTAGES  Range  Linearity  Non-invasive  Obstacles in front of the eye  Cost  Eye closure is permissible  Real Time
    • DISADVANTAGES  One potential problem, depending upon the nature of the experiment would be for the subject to change the gaze by turning the head.  The potential difference between the retina and the cornea may vary with such factors as light adaptation, diurnal variations and the degree of alertness.
    • CONCLUSION  This technique has resulted in rapid advancements in the design of human computer interfaces for severely paralyzed patients, with the aid of this technology many disabled patients who are unable to speak or move their limbs can access many electronic devices such as fan, light etc only through the movement of their eyes.  There is no doubt that this technology will still expand and will have many other applications, and we can expect a future where just a gaze and blink of an eye can be used for control purposes.