ELECTROOCULOGRAM (EOG) - Basics

Electrooculography is a technique for measuring the corneo-retinal standing potential that exists between the front and the back of the human eye. The resulting signal is called the electrooculogram. Primary applications are in the ophthalmological diagnosis and in recording eye movements

1. BASICS OF BIOMEDICAL
ELECTROOCULOGRAM
(EOG)
Prepared by Atheena Pandian

2. What You Will
Learn Today
TOPICS TO DISCUSS
EOG
Principle
Procedure
Observation
Ophthalmological Diagnosis
Measurement
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3. ELECTROOCULOGRAPHY 
(EOG)
It is a technique for measuring
the corneo-retinal standing
potential that exists between
the front and the back of the
human eye.

4. Principle
The eye acts as a dipole in which the anterior pole is
positive and the posterior pole is negative

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

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.

5. To measure eye movement, pairs of
electrodes are typically placed either
above and below the eye or to the left
and right of the eye.
PROCEDURE

6. The patient is asked to switch eye position
repeatedly between two points (alternating
looking from center to the left and from center to
the right). Since these positions are constant, a
change in the recorded potential originates from
a change in the resting potential.
PROCEDURE

7. OBSERVATIONS
If the eye moves from center position toward
one of the two electrodes, this electrode "sees"
the positive side of the retina and the opposite
electrode "sees" the negative side of the retina.

Consequently, a potential difference occurs
between the electrodes.

8. OPHTHALMOLOGICAL
DIAGNOSIS
The EOG is used to assess the function of the pigment
epithelium

During dark adaptation, resting potential decreases
slightly and reaches a minimum ("dark trough") after
several minutes.

When light is switched on, a substantial increase of the
resting potential occurs ("light peak"), which drops off
after a few minutes when the retina adapts to the light.

9. The ratio of the voltages
(i.e. light peak divided by dark
trough) is known as the Arden
ratio. In practice, the
measurement is similar to eye
movement recordings
MEASUREMENT

10. GOOD LUCK