ELECTROOCULOGRAPHY

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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

…contdPlacement of electrodes

Horizontal

Vertical

Reference

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.

THANK YOU