it is a advanced technology that one can easily go through by eye ball movement .it is useful for the handicapped. and which Electro-oculography is used to record eye movements during electronystagmographic testing. It is based on the corneoretinal potential (difference in electrical charge between the cornea and the retina), with the long axis of the eye acting as a dipole. Movements of the eye relative to the surface electrodes placed around the eye produce an electrical signal that corresponds to eye position. Recordings of eye movement are accurate to about 0.5 degree, but it is still less sensitive than visual inspection, which can perceive movements of about 0.1 degree.2 Therefore, visual inspection with Frenzel lenses is sometimes still necessary to document nystagmus of low amplitude. Another limitation of electro-oculography is that torsional eye movements cannot be monitored. Again, visual inspection with Frenzel lenses is sometimes necessary to document torsional nystagmus.2
Fortunately, new techniques have been developed to provide greater accuracy and breadth for oculomotor testing. The most clinically useful technique that has been developed is the infrared video electronystagmographic system. Here, the patient wears goggles that illuminate the eyes with infrared light (invisible to the patient), allowing a small video camera to pick up and project an image of the eyes onto a monitor. This can also assess eye movement in horizontal, vertical, and torsional directions and is more accurate than electro-oculography.EOG records corneoretinal (relative positivity at the cornea and a relative negativity at the retina) potential difference. Any eye movement changes the orientation of the dipole and it is the movement of the dipole that is recorded by the EOG. Gold cup or silver-silver chloride electrodes can be used to monitor the EOG. A typical electrode placement is 1 centimeter superior and lateral to the outer canthus of one eye with a second electrode placed one cm inferior and lateral to the outer canthus of the opposite eye. Both these electrodes are then connected to a single reference electrode, either the same ear or the mastoid process of the temporal bone. Therefore, right outer canthus (ROC) and left outer canthus (LOC) electrodes are referred to as either A1 or A2. In this arrangement, conjugate eye movements produce out-of-phase deflections in the two channels whereas the EEG slow activities contaminating the eye electrodes are in-phase. Both conjugate horizontal and vertical eye movements are detected by this placement scheme. The sensitivity and filter settings for EOG are similar to those used for EEG.
Several varieties of eye movements are recorded during routine PSG: waking eye movements (WEMs), slow eye movements (SEMs), and REMs. During wakefulness both eye blinks and saccadic eye movements produce WEMs. During stage I sleep, SEMs are recorded consistently in the horizontal axis. SEMs generally disappear in the deep
2. • It is a techniquefor 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.
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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.
4. • 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.
6. 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
8. 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
12. ELECTRODES:
• Ag-AgCl Electrode:
• It is atype 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
15. • 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
17. 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.
