Simplifying ERG and EOG....... A topic seldom touched by ophthalmologists due to its apparent complexity !!

1. ELECTRORETINOGRAPHY
(ERG)
&
ELECTROOCULOGRAPHY
(EOG)
Dr Sumeet Agrawal
Vitreo-Retina Fellow
Narayana Nethralaya
Bangalore

2. OVERVIEW
• INTRODUCTION
• HISTORY
• RELEVANT ANATOMY AND
PHYSIOLOGY
• INDICATIONS
• PERFORMING THE TESTS
• INTERPRETATION
• EXAMPLES
• CLINICAL SCENARIOS
• PEARLS AND PITFALLS

3. ELECTRORETINOGRAPH
Y

4. INTRODUCTION
• Electrophysiological test
• Functional status of retina
• Potential change that is related to light-induced
electrical activity within the retina
• Full field ERG is a mass response of the retina
to light stimulus

5. HISTORY
1865 : First known recording of an ERG (amphibian retina) Swedish
physiologist Alarik Frithiof
1877 : Holmgren, James Dewar of Scotland (humans)
1908 : Einthoven and Jolly separated the ERG response into three
components: a-wave, b-wave and c-wave
1941 : American psychologist Lorin Riggs introduced the contact-lens
electrode (clinical use)
1967 : Ragnar Granit Nobel Prize for Physiology and Medicine
(demonstrated the physiology of the receptor potential of each component
of the ERG)
1989 : ISCEV standards
1992 : Erich Sutter mfERG

6. ANATOMY AND PHYSIOLOGY
• Cones maximally
concentrated at the fovea
• But 90% cones located
outside the fovea
• Rods maximum at 15
degrees from fixation

7. • EYEBALL ACTS AS A DIPO

8. STEP 1
OPSIN ACTIVATION
STEP 2
OPSIN ACTIVATES TRANSDUCIN
WHICH ACTIVATES PDE
STEP 3
CYCLIC GMP DECLINES ;
GATED Na+ Channels CLOSE
STEP 4
RATE OF NEUROTRANSMITTER DECLINES

11. • a wave
• from photoreceptors

12.  b wave
 Bipolar cells and the Muller cells.
 Muller cells response extracellular K+
concentration
 K+ released from photorecptors
 Muller cell respond by changing its membrane
potential
 From either cone or rod receptors
 c wave
 Positive wave
 Reflects function of pigment epithelium in
response to rod signals only

14. PHOTOPIC NEGATIVE RESPONSE (PhNR)
• In flash erg Phnr is the negative wave
following the “b” wave
• Amplitude of phnr is measured from the
baseline to the trough of the negative
wave
• This wave is believed to originate from
the ganglion cell layer of the retina and
is earliest affected in glaucoma and
appears before visual field defects

16. TYPES OF ERG
• FULL FIELD ERG
• FOCAL ERG
• MULTIFOCAL ERG
• PATTERN ERG

17. ISCEV
International Society for Clinical Electrophysiology
of Vision
Standardised the protocols for performing
electrophysiological tests (1989)
Ensures uniformity and thus comparability between
labs

18. 1 Dark-adapted 0.01 ERG A rod-driven response of bipolar cells
2 Dark-adapted 3 ERG
Combined responses arising from photoreceptors
and bipolar cells of both the rod and cone systems;
rod dominated
3
Dark-adapted 3
oscillatory potentials
Responses primarily from amacrine cells
4 Dark- adapted 10 ERG
Combined response with enhanced a-waves
reflecting photoreceptor function
5 Light-adapted 3 ERG A cone-driven response of bipolar cells
6
Light- adapted 30 Hz
flicker ERG
A sensitive cone-pathway-driven response
ne L., et al. "ISCEV Standard for full-field clinical electroretinography (2015 update)." Documenta Ophthalmologica 13

19. McCulloch, Daphne
L., et al. "ISCEV
Standard for full-field
clinical
electroretinography
(2015 update)."
Documenta
Ophthalmologica
130.1 (2015): 1-12.

20. Clinical
Electrophysiology
. M Yoka, S Kei.
Retina (5th
edition) Stephen
J Ryan. Section
2, Chapter 8.
Page 202-25.

21. ne L., et al. "ISCEV Standard for full-field clinical electroretinography (2015 update)." Documenta Ophthalmologica 13

22. PERFORMING THE TESTS
• Dark room with non-reflecting walls
• Preparation of the patient
• Pupillary dilatation
• Pre-adaptation to light or dark
• 20 min dark adaptation
• 10 min light adaptation
• Pre-exposure to light
• FFA, Fundus photography should be
avoided
• Fixation
• Should not disturb dark adaptation
• Visible in light adapted state

24. ELECTRODES
GROUND ELECTRODE – FOREHEAD
REFERENCE ELECTRODE – OUTER CANTHUS
ACTIVE ELECTRODE -
Cornea (contact lens electrode) in
flash ERG
Conjunctival sac – used in pattern ERG

29. ELECTRODES

30. LIGHT STIMULUS FOR ERG
stimulus and background light should be homogeneous
and cover the entire retina
• Strobe lamp and LEDs - mobile and can be
easily placed in front of a person whether
sitting or reclining.

31. GANZFELD STIMULATION GLOBE
• The Ganzfeld allows the best control of
background illumination and stimulus flash
intensity.
• Large diameter (40cm) hemispheric dome
with a xenon stroboscopic light bulb placed at
the top of the dome.

33. DARK ADAPTED 0.01
ERG
• Minimum 20 min dark adaptation
• 0.010 photopic cd.s.m-2 ; 0.025 scotopic
cd.s.m-2
• Minimum 2 s interval between flashes
• Rod system response

34. DARK ADAPTED 3
ERG
• Directly following 0.01 ERG
• 3.0 photopic cd.s.m-2 and 7.5
scotopic cd.s.m-2
• Minimum interval 10s

35. DARK ADAPTED 10
ERG
• 10 photopic cd.s.m-2 and 25
scotopic cd.s.m-2
• Interval 20s
• Better defined a wave
• Enhanced oscillatory potentials
• Opaque media / immature retina

36. DARK ADAPTED 3
OSCILLATORY
POTENTIALS
• Filtering out 75 Hz or less from the
ERG waveform from dark adapted 3
ERG
• Taken from 2nd stimulus onwards

37. LIGHT ADAPTED 3
ERG
• 10 min light adaptation
• Back ground luminance : 30 photopic
cd.s.m-2 and 75 scotopic cd.s.m-2
• 3.0 cd.s.m-2 stimuli with 0.5 s interval

38. LIGHT ADAPTED 30 Hz
FLICKER ERG
• Same parameters as light
adapted 3 ERG
• 28 to 33 Hz
• Diascard initial few
responses

39. INTERPRETATION
• AMPLITUDE
• a-wave amplitude : baseline to the a-wave
trough;
• b-wave amplitude : a-wave trough to the b-
wave peak.
• TIME DELAY
• Implicit time (peak time) : onset of the stimulus
to the trough of the a-wave or the peak of the b-
wave

40. INTERPRETATION
• Each lab should have its own normal values
• Adjust for age

41. Clinical
Electrophysiology.
M Yoka, S Kei.
Retina (5th
edition) Stephen J
Ryan. Section 2,
Chapter 8. Page
202-25.

42. • a-wave;
• b-wave and
• Oscillatory potentials (OP)
• (b-wave usually larger than the a-wave)

43. • Oscillatory Potentials
• Reduced amplitude
• time delay
• Both
• implies early diabetic retinopathy, retinal circulatory
disturbances
ophysiology. M Yoka, S Kei. Retina (5th edition) Stephen J Ryan. Section 2, Chapter 8.

44. SUBNORMAL ERG
• Reduced amplitude (proportional
to area of functional retina)
• maintained ratio of a and b waves
• eg media opacities, following
PRP
Clinical Electrophysiology. M Yoka, S Kei. Retina
(5th edition) Stephen J Ryan. Section 2, Chapter
8. Page 202-25.

45. NEGATIVE ERG
• b-wave smaller than a-wave (b/a
ratio < 1)
• Diagnostic value
• Prognostic value
• Central Retinal Vein Occlusion
• Proliferative diabetic retinopathy
• Endophthalmitis

46. NEGATIVE ERG
• b
/
a
<
1
Normal a-wave amplitude
Subnormal a-wave amplitude
Second order neuron abnormality
Combined dysfunction of photoreceptor
and middle retinal layer
Photopic hill phenomenon

47. NEGATIVE ERG
• Congenital
• Complete type congenital stationary
night blindness (CSNB)
• Incomplete type CSNB
• X-linked juvenile retinoschisis (XLRS),
• Juvenileonset neuronal ceroid
lipofuscinosis
• Infantile Refsum disease

48. CONGENITAL STATIONARY NIGHT
BLINDNESS
• Complete and incomplete forms
• On and On-Off bipolar cell dysfunction

50. NEGATIVE ERG
• Acquired causes
• Autoimmune retinopathy
• Birdshot choroidopathy
• Ocular siderosis
• Quinine retinopathy

51. PROGNOSTIC VALUE OF NEGATIVE ERG
ophysiology. M Yoka, S Kei. Retina (5th edition) Stephen J Ryan. Section 2, Chapter 8.

52. ophysiology. M Yoka, S Kei. Retina (5th edition) Stephen J Ryan. Section 2, Chapter 8.

53. IRON INTRAOCULAR FOREIGN BODY
• 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.

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

56. EXTINCT ERG
• Advanced stage of rod– cone
dystrophy,
• Retinitis pigmentosa
• Gyrate atrophy
• Choroideremia
• Leber’s congenital amauorosis
• Autoimmune retinopathy
• Total retinal detachment
• Central retinal artery occlusion

57. ISOLATED CONE
DYSFUNCTIONS
• Rod monochromacy
• Complete form
• Incomplete form
• Selectively decreased photopic responses

58. ophysiology. M Yoka, S Kei. Retina (5th edition) Stephen J Ryan. Section 2, Chapter 8.

59. ROD RECEPTOR
DYSFUNCTION
• Oguchi disease
• Fundus albipunctatus

60. OGUCHI DISEASE
• Absent rod ERG
• Normal cone ERG
• Negative configuration of
combined response; normal
OP
• Photopic hill phenomenon
• Improvement after prolonged
dark adaptation

61. FUNDUS
ALBIPUNCTATUS
• Rod ERG absent after 30 min dark adaptation
• Normal after 3 hour dark adaptation
• Combined response : negative after 30 min, normal
after 3 hours

62. Clinical Electrophysiology. M Yoka, S Kei. Retina (5th edition) Stephen J Ryan.
Section 2, Chapter 8. Page 202-25.

63. ROD-CONE and CONE-ROD DYSTROPHIES

64. FACTORS AFFECTING ERG
 Physiological : Pupil, Age, Sex, Ref.
Error, Diurnal Variation, Dark
adaptation, anesthesia
 Instrumental : amplification, gain,
stimulus, electrodes
 Artifacts : Blinking, tearing, eye
movements, air bubbles under
electrode.

65. MULTIFOCAL ERG
• Limitation of Full Field ERG -
• Unless 20% or more of the retina is affected with a
diseased state the ERGs are usually normal
• Erich Sutter used binary m-sequences to extract
hundreds of focal ERGs from a single electrical
signal
• ERG activity in small areas of retina.

70. • Small scotomas can be
mapped and quantified.
• 61 or 103 focal ERG
responses can be
recorded from the
cone-driven retina.
• 20-30 degrees to each
side of the fovea

71. PATTERN ERG
• Measure of macular function and generalized bipolar
cell function.
• Checkerboard stimulus composed of white and black
squares
• Reduction of PERG amplitude reflect the reduced
activity of dysfunctional RGCs
• Inner retinal activity under light-adaptation.

72. • Principle :
• Net retinal illumination remains
constant. Only a redistribution of
the pattern of light and dark areas
is made

73. • 17” monitor from a distance of 1 meter and
stimulus field is 15 °. 150 stimuli for signal
averaging at a frequency of 1 pulse per second
are used.
• Central fixation is necessary.

74. • Should be used in combination with a traditional light-
adapted luminance ERG to have an index of outer
retina function
• Glaucoma, optic neuritis, ischemic optic neuropathy,
and mitochondrial optic neuropathy
• Can help differentiate Macular from Optic nerve
related pathologies

75. • 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

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

77. ELECTRO-OCULOGRAPHY

78. ELECTRO-OCULOGRAPHY
• Outer retina and retinal pigment epithelium
• Change in the electrical potential between the
cornea and the fundus
• successive periods of dark and light adaptation.
• Standing electrical potential between front and back,
sometimes called the corneo-fundal potential

79. • Mainly derived from the retinal pigment epithelium
(RPE), 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.

81. • 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.

82. • Calibration of the signal
• Gazing at consecutively at two different fixation
points located at known angle apart and recording
the concomitant EOGs .
• Skin electrodes on both sides of an eye the potential
can measure the potential by having the subject
move his or her eyes horizontally a set distance .

86. • 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.

87. Light
switched
off

88. • 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.

89. • Most common use : to confirm Best’s vitelliform
disease
• Clinical utility : Carriers ; end stage disease

91. THANK YOU