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.
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
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 (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.
Four types of eye movements are
Smooth pursuit movements
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
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
The two type of electrodes used are:
It is a type of reference electrode.
The electrode is a silver wire that is coated with a thin layer of
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
Application area is near the eye region
Diameter range is 4-10mm
EOG Signal Filtering and
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
Eye Movement Controlled
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
A two channel amplifier
A laptop (or a microprocessor)
A ZigBee wireless module
Obstacles in front of the eye
Eye closure is permissible
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.
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.