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.