Electroretinography measures the electrical responses of various cell types in the retina, including the photoreceptors, inner retinal cells, and the ganglion cells. Electrodes are placed on the surface of the cornea or on the skin beneath the eye to measure retinal responses.

1. ELECTRORETINOGRAPHY
(ERG)
Prepared by Atheena Pandian
BASICS OF BIOMEDICAL

2. Today's Coverage
Points We'll Discuss
What is ERG?
Photoreceptors
RODS and Cones
Measurements
Eye Response
Recordings
ERG Waves
Diagnose
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Basics of Biomedical

3. Electroretinography meas
ures the electrical
responses of various cell
types in the retina
What is ERG?
Basics of Biomedical

4. Photoreceptors
Photoreceptors are the cells in the retina that
respond to light. Their distinguishing feature
is the presence of large amounts of tightly
packed membrane that contains the
photopigment rhodopsin or a related
molecule.
Basics of Biomedical

5. RODS
Rods are responsible for vision at low light levels (scotopic
vision). They do not mediate color vision, and have a low
spatial acuity.
CONES
Cones are active at higher light levels (photopic vision), are
capable of color vision and are responsible for high spatial
acuity. The central fovea is populated exclusively by cones.
There are 3 types of cones which we will refer to as the
short-wavelength sensitive cones, the middle-wavelength
sensitive cones and the long-wavelength sensitive cones or
S-cone, M-cones, and L-cones for short.
There are two types of photoreceptors in
the human retina, rods and cones.

7. Electrodes are placed on
the surface of
the cornea (DTL
silver/nylon fiber string or
ERG Jet) or on the skin
beneath the eye (Sensor
Strips) to measure retinal
responses
Measurement
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8. Retinal pigment
epithelium (RPE)
responses are measured
with an EOG test with
skin-contact electrodes
placed near the canthi.
Measurement
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9. RECORDING
During a recording, the patient's eyes are
exposed to standardized stimuli and the
resulting signal is displayed showing the
time course of the signal's amplitude
(voltage)
Signals are very small, and typically are
measured in microvolts or nanovolts.
Basics of Biomedical

10. Basics of Biomedical
Eye Response
The ERG is composed of electrical potentials
contributed by different cell types within the
retina, and the stimulus conditions (flash or
pattern stimulus, whether a background light
is present, and the colors of the stimulus and
background) can elicit stronger response from
certain components.

11. Basics of Biomedical
Eye Response
If a dim flash ERG is performed on a dark-
adapted eye, the response is primarily from
the rod system. Flash ERGs performed on a
light adapted eye will reflect the activity of
the cone system.

12. ERG Wave
Sufficiently bright flashes will
elicit ERGs containing an a-wave
(initial negative deflection)
followed by a b-wave (positive
deflection).
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13. Retinitis pigmentosa and related
hereditary degenerations
Retinitis punctata albescens
Leber's congenital amaurosis
Choroideremia
Gyrate atrophy of the retina and
choroid
Goldman-Favre syndrome etc
the electroretinogram (ERG) is used for
the diagnosis of various retinal diseases.
Diagnose

14. GOOD LUCK
Basics of Biomedical