2. ELECTRORETINOGRAM
• Holmgren in 1865 first demonstrated that an
alteration in electrical potential occurred
when light fell on retina.
• In 1877. Dewar recorded light evoked
electrical response, ERG, from humans for
the first time.
• In 1941, Riggs introduced the contact lens
electrode in humans
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3. INTRODUCTION
• Electrodes placed on cornea
• Retina stimulated
• Resultant wave recorded
and analyzed
• Helps study eye, systemic
diseases
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4. ELECTRORETINOGRAPHY
• ERG is a recording of changes in resting potential
in the retina when stimulated with a brief flash of
light.
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5. ERG CONSIST OF
• Electrodes for recording of the resting Potential
• Light stimulating device to deliver standardized flash
of light
• Differential amplifier
Glaucoma
High pressure
Aqueous humor
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6. ELECTRODES
• Three electrodes required
1. Active electrode
Corneal
-Burian Allen (Bipolar)
-Jet electrode (Unipolar)
Non corneal electrode
-DTL fiber electrode (Dawson-Trick-Litzkow)
-Gold foil electrode
-LVP Zari electrode
2. Ground electrode- on patients earlobe
3. Reference or inactive electrode -on patient forehead
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9. LIGHT STIMULATION FOR ERG
• Several methods of stimulating the eye.
• Some laboratories use a strobe lamp that is
mobile and can be easily placed in front of a
person whether sitting or reclining.
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10. GANZFELD
• ERG is recorded using
Ganzfeld which is
integrating sphere
used to deliver stimuli
• Patients over 5 years
of age
• Provides graded
intensity of flash
stimulation, diffuse
background & fixation
lights
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11. • The Grass xenon-
arc photo stimulator
can also be used
for delivering
stimuli.
GRASS XENON-ARC PHOTO STIMULATOR
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12. PROCEDURE
There are many ways of recording ERGs from
patients.
Some laboratories record the light adapted state
first and others dark-adapt first.
Dark adapt the Eye for 30-45min
Anesthetize subjects cornea (paracaine)
Dilate iris (tropicamide; phenylephrine)
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13. RECORDING OF ERG
Attach electrodes:
• Forehead (negative-Reference electrode)
• Corneal (positive-Burian Allen)
• -using non viscous coupler (CMC)
• Behind Ear (Ground electrode)
Patient is made to sit in front of Ganzfeld
Stimualtor
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14. The light stimulus consist of flashes of light of
about 5 ms so that each flash is considerably
shorter than integration time of any photo
receptor
A Standard Flash (SF) strength is defined as one
that produces a stimulus strength of 1.5 – 4.5
candela second per meter square[cd.s/m²]
STIMULUS OF LIGHT
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15. • The a-wave, sometimes called the “late receptor potential“, is
the first negative wave which reflects the general
physiological health of the photoreceptors (rods & cones) in
the outer retina.
• The b-wave is a large +ve wave, reflects the health of the
inner layers of the retina, including the ON-bipolar cells and
the Müller cells
• C-wave: pigment epithelial layer.
• D-wave: off-bipolar cells retina.
ERG
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16. MEASUREMENT OF ERG COMPONENT
• Two principal measures of the ERG waveform are
taken
• : 1) The AMPLITUDE
• a-wave amplitude-from the baseline to the negative
trough of the a-wave,
• b-wave amplitude measured from the trough of the a-
wave to the following peak of the b-wave.
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17. 2) THE TIME (t)
• Latency-time interval between onset of
stimulus and beginning of a wave response
normally its 2ms
• Implicit time-time from the onset of the light
stimulus until the maximum a-wave and b-
wave response.<1/4th of second
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18. TYPES OF ERG
Depending of
the stimulus
zone
• Full field ERG
• Focal ERG
Depending on the
type stimulus
• Single flash ERG
• Flicker Fusion
ERG
• Red flash ERG
• Blue filter ERG
• Pattern ERG
Depending on the
state of retinal
adaptation
• Scotopic ERG
• Mesopic ERG
• Photopic ERG
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19. STANDARDS FOR PERFORMING ERG
Dark adapted, bright (white) flash response
• Generates Max a-wave, b-wave, also
generates OPs :
Dark adapted, dim (blue) flash response
• Isolated rod-driven response
Light adapted, bright flash
• Isolated cone-driven response
30 Hz Flicker
• Another method of isolating cone responses.
ScotopicERG
Photopic ERG
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20. 600
400
200
0
-200
r(µV)
0.30.20.10.0
• It is also called as maximal combined response
• It consist of sharp negative a-wave & a much larger,
rapidly rising b-wave which comes to base line very
slowly
• A standard white flash is used. Difference between
two flash is at least 10 sec (to remove effect of bleach)
DARK ADAPTED, BRIGHT (WHITE) FLASH
RESPONSE (SCOTOPIC)
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21. DARK ADAPTED, DIM (BLUE)
FLASH RESPONSE (SCOTOPIC)
• To isolate signal of Rod system, a dim white flash of (2.5 log
unit below SF)
• A blue stimulus is equally effective
• It is also called as isolated Rod response, has almost no a-
wave , slowly rising & broad b-wave
• b-wave is a post receptor phenomenon i.e inner retinal cell
response driven by only Rod photoreceptor
• With increasing stimulus intensity, amplitude of a wave start
increasing
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22. LIGHT ADAPTED, BRIGHT FLASH
(PHOTOPIC)
• A small a wave & rapidly rising b wave that
rapidly return to baseline
• Better localization of cone fucntions
• Produce due to hyperpolarisation of bipolar
cells & cone photoreceptors
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24. OSCILLATORY POTENTIALS (OPS)
• Oscillatory potentials are small but high frequency
oscillations on ascending limb of b wave of maximal
combined response
• Generated by amacrine cells in middle & inner
retinal cell layer
600
400
200
0
-200
r(µV)
0.30.20.10.0
time (s)
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25. • Other wavelets are removed by resetting of
filters
• Usual setting of filter is at between 0.3Hz to
75 Hz
• To refine OPs filter is set between 75 to 300
Hz to get these high frequency wavelets
-20
0
20
r(µV)
0.120.100.080.060.040.020.00-0.02-0.04
t ime (s)
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26. OSCILLATORY POTENTIALS ARE DELAYED
IN DIABETES
• Reflects retinal ischaemia also seen in CRAO
• Useful in juvenile diabetics >5ys to determine the risk of
proliferative DR.
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27. FLICKER ERG
• Uses the difference in the speed of the rod (slow)
and cone (fast) responses to isolate rod- and cone-
driven function in the retina
FLICKER CONE RESPONSE
• Under photopic condition repetitive stimuli (10 to 30 Hz)
given
• Rods are suppressed & incapable of responding
• Amplitude is measured from trough to crest of each
response which decreases as the flicker increases.
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28. ERG TO 5 SEC OF FLICKER
Three separate stimuli, each with a different frequency
Faster flicker smaller response.DR.ARVIND JAIN 28
29. • A 30 Hz response is sensitive measure of cone
dysfunction, but generated at inner retinal level
• Response is affected in inner retinal ischemic
states
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30. MULTIFOCAL ERG
• This technique is developed by Bearse & Sutter
• The response is recorded from many regions of
retina
• Response is recorded to a scaled hexagonal
reversal stimulus in photopic condition
• It allows assessment of focal retinal function
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34. PATTERN ELECTRORETINOGRAM
(PERG)
• The pattern electroretinogram (PERG) assesses the
retinal response to a structured non-luminance stimulus
such as a reversing black and white checkerboard.
• It provides useful information in the distinction between
optic nerve disease and macular disease in patients with
poor central visual acuity
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36. • CLINICAL USES
• Assessing Visual loss of
unknown etiology
• Diffrentiating visual loss
due to macular
photoreceptor & macular
inner retinal cells
• Monitor drug toxicity
• Assessing glacumatous
damage of retina
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37. LIMITATIONS OF PERG
• Amplitude is very small & require highly
sophisticated equipments
• Not reliable in hazy media
• More Pt. cooperation is required
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38. WHY OBTAIN AN ERG?
• To evaluate retinal function in the obscured fundus.
• To confirm a clinical diagnosis of retinal dysfunction
or specific disease
• To evaluate progression of retinal disease or toxicity
• to facilitate estimation of prognosis (siblings of
patients with inherited degenerations)
• To confirm retinal dysfunction when findings do not
match ocular complaints
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39. • Diagnosis of Retinitis Pigmentosa
• Scotopic (dark-adapted
condition, rod driven) and
photopic (light-adapted, cone
driven) b-wave amplitudes -
these provide the first index of
disease severity and help
differentiate rod-cone from cone-
rod disease.
• Scotopic b-waves reduced by
50% or more - this indicates
progressive disease rather than
a variant of “stationary” disease.
• Early cone system disease - this
frequently reduces the
amplitudes of 30Hz flicker
before photopic b-wave
responses to single flashes.
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40. • Delayed flicker implicit time (from flash to response
peak) - this is a highly sensitive measure of abnormality
and implicit times may be prolonged even with normal
flicker amplitude
• Photopic oscillatory potentials (high-frequency wavelets
of small amplitude that originate in the proximal retina) -
these are generally reduced earlier or to a greater
degree than the photopic, single-flash b-wave, and
oscillatory potentials may be reduced in retinal vascular
diseases.
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41. CONE ROD DYSTROPPY
• the ERGs of a patient with
a cone dystrophy exhibit
good rod b-waves that are
just slower. However, the
early “cone” portion of the
scotopic red flash ERG is
missing.
• The scotopic bright white
ERG is fairly normal in
appearance but with slow
implicit times.
• The 30 Hz flicker and
photopic white ERGs
dependent upon cones are
very poor. DR.ARVIND JAIN 41
42. ERGs in retinal vascular disease.
Vascular occlusions such as central retinal artery thrombosis
produce a characteristic avascular appearance to select areas
of the fundus and an ERG with no b-wave . Ophthalmic artery
occlusions usually result in unrecordable ERGs
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43. • There are many other Less common Retinal
Dystrophy in which ERG is helpful in making
Diagnosis
• Also very useful in estimation of retinal function in
eyes with Opaque media
• Determining Prognosis
• Melanoma associated Retinopathy
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44. Few disorders result in a completely extinguished ERG.
They include the following:
• 1) Leber’s congenital amaurosis
• 2) Severe retinitis pigmentosa
• 3) Retinal aplasia
• 4) Total detachment of retina
• 5) Ophthalmic artery occlusion
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46. • Also useful in monitoring Drug Toxicity of
certain other drugs as
-hydroxychloroquine
-chloroquine
-Thioridazone
Detection of carrier stage (eg. X linked RP, blue
cone monochoromatism)
Retinal Detachment
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47. LIMITATIONS
1. Diurnal variation in rod ERG, so serial measurement
is required
2. Number of artifact can be produced because of -
muscular tension
-blink reflex
-improper electrode placement
3. Age & high refractive error can effect results
4. Flash ERG is affected in only widespread retinal
dysfunction
5. Photophobia, Claustrophobia & Pt.s cooperation
may vary results
6. Disorders involving ganglion cells(tay sach’s ds)
Optic nerve disease, striate cortex – no ERG changes
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