I'm an Consultant Optometrist and I have to share my knowledge about how to measure electrophysiological vision of human eye.

1. OCULAR
ELECTRODIAGNOSTICS
Bimal Kumar Thakur
Consultant Optometrist

2. Introduction
 ERG Electroretinogram
 PERG Pattern ERG
 FERG Focal ERG
 EOG Electrooculogram
 VEP / VECP Visual evoked Potentials
 mfERG / mfVEP Multifocal ERG/ VEP

3. Full field electroretinography

4.  Is the record of diffuse electrical response
 Generated by neural and nonneuronal retinal cells
 Electrical potential generated to flashes of light
 Recorded from the cornea - contact lens electrodes
 Mass response
 Quantifies outer retinal function objectively

5. Ganzfeld Bowl

6. Electrode placement for ffERG

7. Burien Allen Electrodes Gold foil electrode
DTL Electrode
Jet Electrode
Electrodes for ERG recordings

8. ERG Components
 a-wave: negative component - photoreceptors.
 b-wave: positive deflection - Muller and bipolar cells
 c-wave: positive deflection following the b-wave – basal
portion of the RPE.
 Oscillatory Potentials (O.P.): Positive wavelets on the
ascending limb of the b-wave -amacrine cells
 ERP (Early Receptor Potential) :cone photopigments

9. Retinal origins of ERG

10. Clinical Protocol
 Pupil dilation
 25 minutes dark adaptation
 Electrodes
• Burian Allen Electrode
• Jet electrode
• DTL electrode
 Ground electrode attached to the ear lobe
 Recordings as per ISCEV standards

11. ISCEV Standards- ffERG
Recordings
 Single Flash Rod Response
 Maximal (rod-cone) Response
 Oscillatory Potentials
10 minutes light adaptation to blue background
of 30cd/m2
 Single Flash Cone Response
 30 Hz Flicker Response

12. 1. Single Flash Rod Response
b-wave IT
b wave amplitude
•b wave implicit times (in ms)
•b wave amplitudes (in microvolts)
•Rod Photoreceptor contribution
baseline

13. 2. Maximal (rod-cone) Response
baseline
b-wave IT
a-wave IT
b-wave AMP
a-wave AMP
a-wave Implicit time and
Amplitude
b-wave Implicit time and
Amplitude
a-wave – photoreceptors
b-wave- bipolar and muller
cells
b/a ratio – signal transmission
from photoreceptors to bipolar
cells

14. OP1
OP 2
OP 3
OP 4
b-wave IT
a-wave IT
a-wave AMP
b-wave AMP
3. Oscillatory Potentials
4 positive peaks
Contributors – Amacrine cells
4. Single Flash Cone Response
a-wave Implicit time and
Amplitude
b-wave Implicit time and
Amplitude
baseline
baseline

15. 5. 30 Hz Flicker response
b-wave Implicit time and
Amplitude
b-wave IT
b-wave AMP
baseline

16. ROD RESPONSE RODS
RODS + CONES
STANDARD COMBINED RESPONSE
OSCILLATORY POTENTIALS
CONES
SINGLE FLASH CONE RESPONSE
30 Hz FLICKER CONES
amacrine
Scotopic Responses
Photopic Responses
ffERG responses

17. Clinical applications
 Retinitis Pigmentosa
 Juvenile retinoschisis
 Coat's disease
 CRVO and CRAO
 Myotonic dystrophy
 Congenital stationary night blindness
 Oguchi's disease
 Lipopigment storage diseases (Batten's disease)
 Gyrate atrophy
 LCA
 Ocular siderosis

18. Indications for ERG
 Aid to diagnosis in patients suspected of having stationary or progressive
inherited retinal degenerations
• to rule out clinically unaffected family members
• to evaluate possible female carriers of x-linked disease
 To assess patients with retinal toxicity due to metallosis (siderosis)
 Retinotoxic or neurotoxic medications
• chloroquine, Hydroxychloroquine, ethambutol, phenothiazine
• Desferrioxamine, Tamoxifen
 To identify eyes that are likely to develop neovascularization in diseases such as
CRVO and DR
 Documenting therapeutic effects of surgery or medication

19. Limitations
 Ganzfeld ERG requires approximately 20% or more of the
retina to be dysfunctional – abnormal ERG
 < 20% of the retina is affected with a diseased state - ERGs are
normal.
 Legally blind person with macular degeneration, enlarged blind
spot or other central scotomas will have normal global ERGs

20. Multifocal electroretinogram

21.  Developed by Prof. Sutter and Tran (1992).
 Simultaneous recording of focal retinal responses in a brief
period of the time
 Offers direct, objective and topographical mapping of central
36-40º of retinal function.
 mfERG responses are cone driven responses
 The health of the fovea, Para fovea and near peripheral photopic
retina can be evaluated.

22.  Difference between full field ERG and mfERG
• Method of stimulation
• Recovery of the ERG response
 Scaled hexagonal array stimulus- stimulate individual retinal
areas
 Commonly used 103 hexagonal array
 Each hexagon flickers between 2 binary states ie., black &
white
 Controlled by predetermined pseudorandom binary m-sequence

23.  Hexagonal stimulus to compensate for local differences in
cone density
 Standard protocol- central hexagons smaller than peripheral
 Scaled to produce local retinal responses of equal amplitude
 Frame changes for every 13.33msecs (a frame rate of 75 Hz)
 CRT device to deliver multifocal stimulus

24. 103 hexagonal stimulus array

25. CRT Monitor

26. 1.6 °
1.6°- 6°
6°-11.4°
11.4°-18.2°
18.2°-26.2°
26.2°-35°
•Waveforms grouping according to different retinal eccentricities
•Subtends 35° horizontally and 31° vertically – viewing distance 53cm
•The responses obtained from six zones

27. Multiplot
Trace Array

28. mfERG Components
 N1 – First negative trough
 P1- First positive Peak
 Origins
• Cone Photoreceptors
• Dominated by on and off bipolar cells
N1- IT
P1-IT
P1- AMP
N1-AMP

29.  Degenerative photoreceptor disease
• Larger delay in implicit times
 Local lesions damaging INL
• Larger reduction in amplitudes
 Damage to NFL or GCL
• No reduction or delay

30. Clinical applications
 To distinguish retinal diseases from optic nerve disease
 Details extent of lesion
 Sensitive indicator for retinal drug toxicity
 Post-operative management following V-R surgery
 Assess sub-clinical retinal changes in DR

31. Stargardt’s disease
Fullfield ERG

32. Multifocal ERG –
Trace array

33. Multiplot

34. Fullfield ERG
Retinitis Pigmentosa

35. Multifocal ERG –
Trace array

36. MultiPlot

37. Fullfield ERG
Cone Dystrophy

38. Multifocal ERG –
Trace array

39. Multiplot

40. Electrooculogram

41.  Measure of RPE function.
 Measure of the constant standing potential of
approximately 6mV that exists between the cornea
and the back of the eye
 Interaction between the RPE and Photoreceptors
 Recorded during successive periods of dark and light
adaptation

42. Electrode placement for EOG

43. 16-20 sweeps per minute
30 degree lateral eye movements

44. Arden’s Ratio = Light peak x 100
Dark trough
5 minutes
8-12m 6-9m

45. Arden’s ratio
 > 1.85- Normal
 1.65-1.80- marginally subnormal
 <1.65-distinctly subnormal

47. Applications
 Best Vitelliform macular dystrophy
 Butterfly pattern dystrophy Acute zonal occult outer
retinopathy
 Punctate inner choroidopathy
 Multifocal choroiditis
 White dot syndrome

48. Visually Evoked Potentials (VEP)

49.  Signal generated by visual cortex in response to visual
stimulation
 Electrodes – scalp
 Main signal – occipital region of cortex
• Predominantly macular function
 Central 2* of visual field
• Contributes 65% of VEP responses

50. VEP stimuli
 Flash/ pattern / color/ motion
 Flash and pattern stimuli
 Flash VEP – Ganzfeld stimulator
 Pattern VEP – CRT monitor

51. Electrode placement
 Based bony landmarks
 Proportion of size of head
 Active electrode – scalp over visual
cortex
 Reference electrode – midline
 Ground electrode – forehead
 Impedance ≤ 5kΩ

53. FLASH VEP - PARAMETERS
P2 LATENCY – 125ms
P2 AMP - >10µV

54. Indications
 Uncooperative or unconscious patients
 Media opacities
 With penetrating wounds to the globe
 Selection and timing of vitreous surgeries

55. PATTERN VEP - PARAMETERS
P1 LATENCY – 100-110ms
P1 AMP - >5µV

56. Indications
 Optic neuritis
 Multiple sclerosis
 Compressive optic neuropathy
 Unexplained visual loss
 Amblyopia
 Malingering
 Traumatic brain injury
 Pre-surgical evaluation
 Measuring visual acuity in non-responsive subjects

57.  Multifocal VEP:
• Objective assessment of visual field
• Multiple areas stimulated
independently and simultaneously
• Accurate in testing local defects in
visual field
• Glaucoma
• Optic nerve disorders