The document discusses various electrophysiological tests used in ophthalmology, including electroretinogram (ERG), electro-oculogram (EOG), and visual evoked potential (VEP), describing their types, waveforms, and clinical indications. It highlights the significance of these tests in diagnosing retinal and optic nerve conditions, along with the physiological factors that can affect their results. Additionally, the document details the methodology for performing these tests, typical abnormalities observed, and their relevance in differentiating between ischemic and non-ischemic retinal diseases.

1. ELECTRO
PHYSIOLOGICAL
TESTS
Moderator : Dr Rajesh R Nayak
Presenter : Dr Sriraj Alapati

2. INTRODUCTION
 ERG : NSR
• Photoreceptors – rods & cones (a-wave)
• Inner Retina – bipolar, muller (b-wave)
 EOG : RPE
VEP : Optic nerve to visual cortex

3. Measures the change in resting potential of the eye induced by a
flash of light, resulting in a biphasic waveform which is recorded
using electrodes.
Electrophysiological test of NSR (photoreceptors & bipolar cells)
A. ELECTRORETINOGRAM (ERG)
TYPES
• Multifocal ERG

4. 1ST
order : Bipolar cells
2nd
order : Ganglion cells
3rd
order : LGB
PHYSIOLOGY

5. Description RODS CONES
Number 120 M 6 M
Location Mid periphery (bony spicules in RP) Fovea
Types 1 3 (L, M; S) : 2nd
CN#; retina, macula#
Pigment Rhodopsin Phorphyropsin (proton): red (XLR) 555nm
Iodopsin (deutron): green (XLR) 530nm
Cyanopsin (triton): blue (Chr 7) 426nm
LGB (3rd
order) Ventral Magnocellular (WHERE) 1
Affected in glaucoma
Dorsal Parvocellular (WHAT) 8
Light conditions Dim light (Night vision) : scotopic Bright light (Day vision) : photopic
Type of vision Black and white (Achromatic) Color vision (chromatic)
Functions Peripheral vision
Gross vision, stereopsis
Contrast & motion sense
Central vision
Fine vision, stereopsis
Abnormality Nyctalopia Dyschromatopsia, Hemeralopia

7. Electrodes:
• Ground - forehead
• Reference – outer canthus
• Active - cornea contact, conjunctival
HOW TO PERFORM?

8. WAVE FORMS

9. A wave B wave
Negative (hyperpolarization) Positive (depolarization)
Outer retina (Photoreceptors) – rods & cones Inner retina (INL) – bipolar ON, muller
Choroidal pathology ? (20 short PCA) Retinal pathology ? (CRA)
Rod a wave (scotopic) – broad
Cone a wave (photopic) – sharp
B1 – rod cone (scotopic) : slow rising, broad peak
B2 – cone (photopic) : rapid rising, sharp peak

10. C wave:
Small positive
RPE
D wave:
Positive, photopic
Bipolar OFF
OP’s (oscillatory potentials):
Amacrine
Flicker response:
Cone driven

11. Scotopic/DA 0.01 - rods (b wave)
Scotopic/DA 3.0 - mixed
Scotopic/DA 10.0 – mixed, strong
Scotopic/DA 3.0 OP’s - amacrine
Photopic/LA 3.0 - mixed
Photopic/LA 3.0 flicker - cones
1. Full Field (Ff ERG)

13. Indications

14. NEGATIVE ERG
Reduced b wave or b/a ratio
Negative b, a waves
• RP
• CRVO, CRAO
• CSNB
• Cone dystrophy
• HCQ
EXTINGUISHED ERG
Absent b, a waves
• Advanced RP
• OIS
• Leber's congenital amaurosis
• Retinal aplasia
• RD
• Choroideremia

15. Reduced cone responses in
cone dystrophy
Reduced scotopic rod &
combined responses in early RP

16. Retina has dual Blood Supply
1. Outer 4 Retinal layers (Photoreceptors) : PCA
'a' wave lost in choroidal #
2. Inner 6 Retinal layers (INL) : CRA
'b' wave lost in retinal #
INNER RETINAL ISCHAEMIA
I. b/a ratio or b wave amplitude reduced
II. OP’s absent (DA 3.0 OP – amacrine)
III. Flicker implicit time prolonged (LA 3.0 flicker – cones)
IV. Interocular difference
ERG In Vascular Retinopathies
USES :
1. Non ischemic Vs
Ischemic CRVO
2. CRAO Vs OIS
3. NPDR Vs PDR

17. Non ischemic Vs Ischemic CRVO

18. ERG > FFA ? in CRVO:
1.Non-Invasive
2.Detects Inner retinal ischaemia
3.Not limited by the wide field
4.Not limited by media opacity
5.Not limited by Retinal hg’s / Oedema
6.Not limited by Systemic co-morbidities
• RAPD
• ERG
• RAPD + ERG (most reliable 97%)
• HFA (VF)
• FFA (RETINAL CAPILLARIES obliterated - non perfusion)
• Fundus could mislead (splashed tomato sauce appearance)

19. • Ophthalmic artery occlusion
• Mid periphery retinal hg’s, MA,
dilated veins, NVE, NVG
• Suspect in U/L DR changes
• Do carotid artery doppler
• Extinguished ERG (a, b absent)
OIS

20. CRAO
• Retinal whitening, Cherry red spot,
attenuated arteries, dilated veins,
cattle truckling of veins.
• Do carotid artery doppler
• Negative ERG (a, b negative)

21. NPDR Vs PDR

22. 2. Multifocal (Mf ERG)
Only cones (LA)
Mathematical extraction
Topographic mapping
Pupillary dilation
Refractive correction
103 hexagonal units
Kernel responses
Central fixation dots & circles
Mf ERG don’t replace Ff ERG
USES : HCQ, desferoxamine toxicity
CSCR, RP, stargardts

24. > 5 mg/kg/day
Cv abnormal
Fundus : bulls eye maculopathy
HFA 10-2 : paracentral scotomas
OCT : disruption of parafoveal EZ
FAF : parafoveal hyperAF
Abnormal Mf.ERG
HCQ

25. 3. Pattern (P ERG)
P50 - macular photoreceptors
N95 - GCL

26. Physiological -
• Age : newborns have immature ERG
• Gender : females have higher amplitude b waves
• Refraction : myopes have lesser amplitude b waves
• Diurnal Variation : daylight have lesser amplitude rod b waves
• Pupillary size : small pupil have lesser amplitude waves
• Media clarity : VH have unrecordable ERG
• Uveal pigment : albinism have higher amplitude waves
• Dark adaptation
• Medications : alcohol, GA, steroids
Technical - electrodes, stimulus parameters, filters, amplifiers
Variations In ERG

27. B. ELECTRO-OCULOGRAM (EOG)
Standing potential of eye : Difference in electrical
potential between anterior & posterior part of the eye
Electrophysiological test of RPE
• Dilated pupils
• Electrodes
• Ganzfeld dome

28. 1. Saccades 10s of each min
2. Wave form
3. Dt (dark trough) : 15 mins
4. Lp (light peak) : 15 mins
5. Ardens ratio Lp/Dt
Components of EOG

29.  Normal > 1.80
 Subnormal 1.65 to 1.80
 Abnormal < 1.65
Ardens ratio :
light peak (Lp)/dark trough (Dt)

30. 1. Good saccades
2. Sine wave
3. No dark trough
4. No light peak
5. Abn Arden ratio

31. V/A - Normal

32. Fundus ERG EOG
AD Best vitelliform (V/A – N) Macula Normal Abnormal
AR Bestrophinopathy Vascular arcades Abnormal Abnormal
AD vitreoretinochoroidopathy Vitreous Abnormal Abnormal

33. C. VISUAL EVOKED POTENTIAL (VEP)
Electrical signal generated at visual cortex in response
to visual stimulation.
Electrophysiological test from Optic nerve to visual
Cortex (Central VF).
Electrodes :
• Occipital lobe (Oz, active/positive)
• Forehead (Fz, reference/negative)
• Earlobe/vertex/mastoid
(ground/neutral)

34. Types
Waveforms

35. Optic neuritis - Multiple sclerosis
AION
Optic atrophy
Toxic neuropathy
TON
Pattern Reversal VEP
(optic neuropathy)
Visual function of babies
Non-responsive subjects
Unexplained visual loss
Flash VEP
Amblyopia
Malingering
Nystagmus
Pattern on/off VEP
Indications

36. VEP Amplitude Latency/Implicit time
AION Reduced Normal
Optic neuritis Reduced Increased/Delayed
TON Reduced Increased/Delayed
Optic atrophy Absent No signal
Toxic neuropathy Normal Increased P100
Pattern reversal
VEP

37. THANK YOU