ERG EOG

1.  Electroretinogram
 Electrooculogram
 Anuraag
Singh

2. ERG
 History
Holmgren in 1865 first demonstrated that
an alteration in electrical potential
occurred when light fell on retina.
 In1877. Dewar recorded light evoked
electrical response, ERG, from humans
for the first time.
In1941, Riggs introduced the contact lens
electrode in humans

3. ERG
 Full-field Electroretinogram (ERG) is a
mass electrical response of the retina to
photic stimulation.
 Basic method of recording is by
stimulating the eye with a bright light
source such as a flash produced by LEDs
or a strobe lamp.
 The flash of light elicits a biphasic
waveform recordable at the cornea.

4. Basic wave forms
 The two components that are most often
measured are the a- and b-waves.
 a-wave is the first large negative
component, followed by the b-wave which
is corneal positive and usually larger in
amplitude

5. Physiology of ERG
 “a” wave aka late receptor potential
 When light falls on photo receptors
 Hyperpolarisation
 Outer portion of photoreceptor becomes
positive
 Inner part becomes negative
 A wave shows downward deflection
 Reflects the potential of photoreceptors in outer

6. b wave
 b wave - Reflects the function of the inner
layers of the retina, including the ON
bipolar cells and the Muller cells.
 Muller cell is a glial cell ( has no synaptic
connection )
 It respond to potassium concentration in
extracellular space

7.  Light strikes a photoreceptor
 Potassium released from photorecptors
( amount dependent on Light Intensity )
 Muller cell respond by changing its
membrane potential
 b wave is dependent on the electrical
activity within photoreceptors
 Muller cells can provide a b wave from
eithyer cone or rod receptors

8. c Wave
 Positive wave
 Reflects function of pigment epithelium in
response to rod signals only
 d wave
 Reflects Off bipolar cells

10.  Ops - some wavelets that occur on the rising
phase of the b-wave known as oscillitatory
potentials (OPs).
 OPs are thought to reflect activity in amacrine
cells

11.  Two principal measures of the ERG
waveform are taken:
 1) The amplitude
 2) The time
Amplitude:-
 a wave- from the baseline to the negative
trough of the a-wave
 b-wave measured from the trough of the a-
wave to the following peak of the b-wave
Time:-
 (t)a from flash onset to the trough of the a-
wave (t)b from flash onset to the peak of the
b-wave
 These times, reflecting peak latency, are

13. ERG recording electrodes
 Pupils are dilated
 Different types of electrodes used
 Burian Speculum that hold the eye open
and have a contact lens with a wire ring
that “floats” on the cornea supported by a
small spring.
 Cotton wick electrodes
 Gold Mylar tape that can be inserted
between the lower lid and sclera/cornea.

17. Light stimulation for ERGs.
 Strobe lamp and LEDs - mobile and can be
easily placed in front of a person whether sitting
or reclining.
 Mobility of a strobe lamp or an array of LEDs is
a necessity in some situations such as at the
hospital bedside or in the operating room

18. Ganzfeld stimulation globe
 The Ganzfeld allows the best control of
background illumination and stimulus
flash intensity.

19. Rod and cones erg
 Implicit times and amplitudes vary
depending upon whether the eye is dark
adapted or not, and brightness and color
of the light stimulus.
 These parameters allow separation of rod
and cone activity in retina.
 Normally there are120 million rods in each
retina and about 6-7 million cones.
 The ERG following a white flash is
dominated by the mass response of the
rods( due to large number )

20. Rod and cone activity can be isolated
 Adaptation level
 Background illumination
 Rate of stimulation
 Color of the flash
 Flash intensity

21. Color stimulus
 Peak wavelength sensitivity for rods is around
510 nm and the peak sensitivity of cones as a
group is about 560 nm
 By using color filters such as the Kodak Blue
and Red Wratten series rods and cones can be
differentiated

22.  Rod and cone ERGs can also be isolated using
dim flash stimuli into photopic (cone)and
scotopic (rod) signals
 Dim red flashes stimulate both rod and cone
function producing a small photopic component
bx and larger rod b-wave.
 Rods are about three log units more sensitive
than cones.
 Cones recover faster than rods.

24. Rate of stimulus
 Rates (flicker) of stimulus presentation
also allows rod and cone contributions to
the ERG to be separated.
 Even under ideal conditions rods cannot
follow a flickering light up to 20 per
second whereas cones can easily follow
a 30 Hz flicker.
 This is the rate routinely used to test if a
retina has good cone physiology.

26. Types of ERG

27. Standard Full Field ERG
 ISCEV Standard ERG Protocol
 In 1989, the International Society for
Clinical Electrophysiology of Vision
(ISCEV) developed a protocol to
standardize ERG testing so test results
could be compared worldwide.
 The protocol consists of five separate
tests, each designed to evaluate different
areas or functions of the eye.

28. Dim Scotopic Flash ERG
 This is the first step in the International
Society for Clinical Electrophysiology of
Vision (ISCEV) standard ERG protocol.
 It is conducted with a -25 dB flash.
 In a dark-adapted eye, a dim flash tests
a response arising from the rods primarily
and associated glial cells.

29. Maximum Scotopic Flash
ERG This is the second step in the
International Society for Clinical
Electrophysiology of Vision (ISCEV)
standard ERG protocol.
 It is conducted with a 0 dB flash.
 In a dark-adapted eye, a moderate flash
tests a response from both the rods and
cones.

30. Oscillatory Potentials (OPs)
 This is the third step
 The oscillatory potentials are high-frequency
oscillations or wavelets seen on the leading-
edge of the b-wave.
 The oscillatory potentials measure of function of
the amacrine cells and become abnormal early
in retinal ischemia.

31. Photopic Flash ERG / Single
Flash
Cone Response This is the fourth step
 It is conducted with a 0 dB flash. In a
light-adapted eye, a moderate flash tests
a response arising from the cones

32. 30 Hz Flicker ERG
 This is the fifth step
 In a light-adapted eye, a flicker ERG tests
a response arising from the cones.
 The flicker ERG has also been shown to
be useful in patients with diabetic
retinopathy.

33. ERG in Retinitis pigmentosa

34.  The first two responses are scotopically matched
blue and red ERGs.
 The blue flash was dim enough that no a-wave can
be discerned in a normal patient leaving only the rod-
dominated slower b-wave.
 The red flash is bright enough that photopic
oscillations and bx component can be observed just
after the a-wave.
 Bright white flash in the dark produces the largest
amplitude ERG.
 The 30 Hz flicker illustrates the response of the
rapidly recovering cones.
 Photopic response is representative of a normal
response with the more sensitive rods bleached by
background illumination.
 Oscillatory potentials on the ascending b-wave are
seen in responses to moderate-high intensity white
flashes and in response to red, yellow, and green

35. Stationary rod dystrophies
 Congenital stationary night blindness
(CSNB) is found in several forms.
 Two types.
 Type 1 have an abnormal dim scotopic
ERGs but the bright flash ERG maintains
oscillatory potentials on the ascending
limb of the b-wave.
 Type 2 has a very abnormal dim scotopic
ERG and the bright flash scotopic ERG
has a large a-wave and no b-wave.
 Oscillatory potentials are also missing

37. The bright flash ERG b-wave is selectively attenuated
in:
 Juvenile retinoschisis
 Coat’s disease
 Central retinal vein occlusion and central retinal artery
occlusion
 Myotonic dystrophy
 Congenital stationary night blindness Type 2
 Oguchi’s disease
 Lipopigment storage diseases (Batten’s disease)
 Creutzfeldt-Jacob (CJD)

38. Disorders result in a completely extinguished
ERG
 Leber’s congenital amaurosis
 Severe retinitis pigmentosa
 Retinal aplasia
 Total detachment of retina
 Ophthalmic artery occlusion

39. ERG in cone dystrophies
 ERGs of a patient with a cone dystrophy
exhibit good rod b-waves that are just
slower.
 The early “cone” portion (bx) 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.

41. ERGs in retinal vascular disease
 Vascular occlusions –
avascular appearance to
select areas of the fundus
 ERG with no b-wave
 Ophthalmic artery
occlusions usually result
in unrecordable ERGs.

42. Foreign bodies and Trauma
 A small piece of stainless steel or plastic
outside the macula may have a minor
affect on the retina.
 A piece of copper or iron have deleterious
affects within a few weeks
 In general if b-wave amplitudes are
reduced 50% or greater compared to the
fellow eye, it is unlikely that the retinal
physiology will recover unless the foreign
body is removed.

44. Drug toxicities.
 Several drugs taken in high doses or for
long periods of time can cause retinal
degeneration with pigmentary changes.
 Thioridazine
 Chlorpromazine
 Vigabatrin
 Chloroquine
 Hydroxychloroquine
 The effects of toxic medications can be
detected and quantified using ERGs.

45.  The effects of toxic medications can be
detected and quantified using ERGs.
 Chloroquine retinopathy appears as a
characteristic “bullseye” maculopathy

46.  The better substitute for chloroquine,
Plaquenil, can also have macular effects
noticeable by multifocal
electroretinograms.
 Hydroxychloroquine (Plaquenil) is usually
less disruptive to the retina than
chloroquine, but ERG changes can still
occur.
 Vigabatrin, a pediatric seizure medication,
can be toxic to the retina.
 Attenuation of full-field ERG b-wave
amplitudes can detect toxicity.
 Often the first indication of toxicity is

47.  Cis-platinum used to treat brain tumors
sometimes reaches ophthalmic vascularization
and causes a reduction in ERG waveform in the
affected eye (OD in this case)


48. Steroid Retinopathy
 The fundus photo shows a cherry red
spot in the macula. The ERG response
was diminished in size particularly
following dim scotopic flashes

49. Talc retinopathy
 Seen in iv drug abusers
 Global ERG is attenuated

50. Multifocal erg
 Limitation of fferg - Unless 20% or more
of the retina is affected with a diseased
state the ERGs are usually normal.
 Erich Sutter adapted the mathematical
sequences called binary m-sequences
creating a program that can extract
hundreds of focal ERGs from a single
electrical signal.
 This system allows assessment of ERG
activity in small areas of retina.
 mferg allows assessment of ERG activity
in small areas of retina.

52.  With this method one can record mfERGs
from hundreds of retinal areas in a
several minutes

53. merg in macular degeneration

55.  Small scotomas in retina
can be mapped and degree
of retinal dysfunction
quantified.
 61 or 103 focal ERG
responses can be recorded
from the cone-driven retina.
 The tested area typically
spans 20-30 degrees to
each side of the fovea

56. Pattern erg
 The pattern ERG provides a useful
measure of macular function and
generalized bipolar cell function.
 The most common stimulus is a
checkerboard stimulus composed of
white and black squares
 PERG generation requires physiological
integrity of anatomically present RGCs
 Reduction of PERG amplitude reflect the
reduced activity of dysfunctional RGCs

57.  PERG reflects inner retina activity under
light-adaptation.
 The PERG should be used in
combination with a traditional light-
adapted luminance ERG to have an index
of outer retina function
 PERG represents an important tool to
monitor the onset and the progression of
RGC dysfunction in optic nerve disease.
 Example:-
 Glaucoma, optic neuritis, ischemic optic
neuropathy, and mitochondrial optic
neuropathy

59.  The normal pattern electroretinogram :
 N35- a small negative component with a
peak time occurring around 35 ms;
 P50- a prominent positive wave emerging
around 50 ms
 N95- a wide negative wave around 95 ms

61. perg in Macular diseases:-
 The P50 component was shown to be
altered in all patients with retinal and
macular diseases.
perg in Optic nerve disease:-
 N95 component was abnormal in 81% of
patients with diseases of the optic nerve.
The P50 component remain normal.

63. ELECTRO-OCULOGRAPHY
 Electrophysiological test of function of the
outer retina and retinal pigment epithelium
in which the change in the electrical
potential between the cornea and the
fundus is recorded during successive
periods of dark and light adaptation.
 The eye has a standing electrical potential
between front and back, sometimes called
the corneo-fundal potential

64.  The potential is mainly derived from the
retinal pigment epithelium (RPE), and it
changes in response to retinal illumination
 The potential decreases for 8–10 min in
darkness.
 Subsequent retinal illumination causes an
initial fall in the standing potential,
followed by a slow rise for 7–14 min (the
light response).
 These phenomena arise from ion
permeability changes across the basal
RPE membrane.

66.  The clinical electro-oculogram (EOG)
makes an indirect measurement of the
minimum amplitude of the standing
potential in the dark and then again at its
peak after the light rise.
 This is usually expressed as a ratio of
‘light peak to dark trough’ and referred to
as the Arden ratio.

67.  The calibration of the signal may be
achieved by having the patient look
consecutively at two different fixation
points located at known angle apart
and recording the concomitant EOGs .
 By attaching skin electrodes on both
sides of an eye the potential can be
measured by having the subject move
his or her eyes horizontally a set
distance .

72. Standard method
 After training the patient in the eye
movements, the lights are turned off.
 About every minute a sample of eye
movement is taken as the patient is
asked to look back and forth between the
two lights .
 After 15 minutes the lights are turned on
and the patient is again asked about once
a minute to move his or her eyes back
and forth for about 10 seconds.

74.  Typically the voltage becomes a little
smaller in the dark reaching its lowest
potential after about 8-12 minutes, the so-
called “dark trough”.
 When the lights are turned on the
potential rises, the light rise, reaching its
peak in about 10 minutes.
 When the size of the "light peak" is
compared to the "dark trough" the relative
size should be about 2:1 or greater .
 A light/dark ratio of less than about 1.7 is
considered abnormal.

75. Clinical uses of EOG
 Retinal diseases producing an abnormal
EOG will usually have an abnormal ERG
too which is the better test for analysis of
scotopic and photopic measures.
 A particularly good use for the EOG is in
following the affects of high dosage
treatment with antimalarials such as
chloroquine and plaquenil over the course
of treatment and before the ERG is
affected

76.  Most common use of the EOG nowadays
is to confirm Best’s vitelliform disease
 Vitelliform lesions represent the
accumulation of lipofuscin in the macular
area. Further effects of retinal pigment
epithelium (RPE) dysfunction include
accumulation of degenerated
photoreceptor outer segments in the
subretinal space.