electro oculography
TRANSCRIPT
ELECTRO OCULOGRAPHY
.
• It is a technique for measuring
the resting and action potential of
the retina.
• 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.
PRINCIPLEThe 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 negative-trending change
in the recorded potential difference.
2.Right gaze: the Cornea approaches the
electrode near the inner Canthus of the left
eye, resulting in a positive - trending
change in the recorded potential difference.
• The 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
anterior pole
EOG Detection
• Four to five electrodes are required.
• 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
Placement of electrodes
• Horizontal
• Vertical
• Reference
EOG Signals• HEOG Signals: Obtained from horizontal eye movements
• Eye movement: from center to left: +ve voltage spike from center to right:-ve
voltage spike
• VEOG Signals: Obtained from vertical eye movements
• Eye movement: from center to top: +ve voltage spike from center to bottom: -ve voltage
spike
• Blink Signals: Obtained due to blinking of eyes
• Voluntary Blink Signals
• Involuntary Blink Signals
Block diagram
GRAPH
ELECTRODES :• 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.
• 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
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
• 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 microprocessor
• A wireless module
ADVANTAGES
• Range
• Linearity
• 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.