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Investigative Optometry and Case Studies > ERG > Flashcards

ERG Flashcards

not including pattern ERG lecture (61 cards)

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1
Q

What are the types of electrode?

A

Burial Allan CL
Gold foil
DTL
Skin

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2
Q

What is the Burial Allan CL electrode?

A

Scleral CL with a bipolar electrode

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3
Q

What are the advantages of the Burial Allan CL electrode?

A

Large, repeatable signal

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4
Q

What are the disadvantages of the Burial Allan CL electrode?

A

Impairs vision
Uncomfortable
Can use for max 30 mins at a time
Needs anaesthetic

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5
Q

What is a gold foil electrode?

A

J-shaped, tail sits in lower fornix

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6
Q

What are the disadvantages of the gold foil electrode?

A

Can fall out
Can cause reflex tearing and irritation
Smaller signal than CL electrode

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7
Q

What are the advantages of the gold foil electrode?

A

No anaesthetic needed
Vision not impaired

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8
Q

What is the DTL electrode?

A

7 strands of nylon with silver impregnated, inserted into lower fornix

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9
Q

What are the advantages of the DTL electrode?

A

Comfy
Vision not disrupted
No anaesthetic needed

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10
Q

What are the disadvantages of the DTL electrode?

A

Signal is smaller than CL electrode

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11
Q

What is a skin electrode?

A

‘Sticker’ placed on skin under lower lid

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12
Q

What are the advantages of a skin electrode?

A

Vision not disrupted
Comfy
No anaesthetic needed
Good for kids and babies

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13
Q

What are the disadvantages of a skin electrode?

A

Very small signal

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14
Q

What equipment is needed to perform an ERG?

A

Stimulus
Electrodes
Preamplifier
Main amplifier

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15
Q

What does the preamplifier do?

A

Boosts ERG signal
Protects px from electrocution as not on mains power

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16
Q

What does the amplifier do?

A

Amplifies signal
Filters, rejects and averages signal

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17
Q

What are the types of stimulation?

A

Full field
Focal
Pattern

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18
Q

What are the characteristics of full field stimulation?

A

Whole retina stimulated
Large signal
Unable to give focal result

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19
Q

What are the characteristics of focal stimulation?

A

4 different wavelengths can be shown
Duration and temporal frequency adjustable
Causes some scatter so secondary wave is created

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20
Q

What are the characteristics of pattern stimulation?

A

Checkerboard
Can be reversed or on/off sequence
No scatter created
RE must be corrected for accurate result

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21
Q

What is seen in the waveform when the stimulus is shown at short frequencies?

A

Typical waveform is seen

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22
Q

What is seen in the waveform when the stimulus is shown at long frequencies?

A

Steady state waveform: stages blur into each other
No retinal recovery seen
Seen at ~30hz
Detects cone activity

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23
Q

What is the protocol for undertaking an ERG?

A
  1. Explain to px
  2. Dilate pupils
  3. Clean skin
  4. Attach earth and reference electrode
  5. Attach DTL electrode
  6. Check electrode resistance
  7. Select stimulus
  8. Set up computer (filters etc)
  9. Test recording
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24
Q

List the ISCEV standards

A

Scotopic 0.01 ERG
Scotopic 3.0 ERG
Scotopic 10 ERG
Scotopic 3.0 OPs
Photopic 3.0 ERG
Photopic 3.0 Flicker

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25
What are the characteristics of the Scotopic 0.01 ERG?
Dark adapted for 20 mins Dim flash 2 second frequency between flashes Detects B-wave
26
What are the characteristics of the Scotopic 3.0 ERG?
Dark adapted Bright flash 10-second frequency between flashes Detects A-wave, B-wave and OPs
27
What are the characteristics of the Scotopic 10 ERG?
Dark adapted for 20 mins V bright flash 20-second frequency between flashes Detects increased A-wave and enhanced OPs
28
What are the characteristics of the Scotopic 3.0 OPs?
Recorded at same time as Scotopic 3.0 ERG Dark adapted for 20 mins Bright flash 10-second frequency between flashes Detects OPs on B-wave
29
What are the characteristics of the Photopic 3.0 ERG?
Light adapted for 10 mins Bright flash 0.5 second frequency between flashes Cone response Response is smaller than scotopic ERG
30
What are the characteristics of the Photopic 3.0 Flicker?
Light adapted for 10 mins Bright flash flickers at 30 hz Cone response Gives steady state response with a periodic waveform
31
What are the components of Granit's analysis?
PI PII PIII
32
What is PI?
Slow positive response Gives rise to C-wave
33
What is PII?
Moderately fast positive response with peak and plateau Gives rise to B-wave
34
What is PIII?
Fast and slow negative response Gives rise to A-wave
35
How can retinal origin be determined?
Current source density analysis Intracellular recordings Pharmacological testing
36
How does current source density analysis work?
Microelectrodes measure electrical flow
37
How do intracellular recordings work?
Specific cell type electrical activity is compared to the ERG
38
How does pharmacological testing work?
Drugs are used to block synapses, giving a reduced response from some cell types
39
What are the characteristics of the Early Receptor Potential (ERP)?
Only present when the stimulus is very bright and <1ms Biphasic: positive then negative Originates from PR OS
40
What are the characteristics of the A-wave?
Negative potential 15ms latency Corresponds to PIII in Granit's analysis Originates from PRs (discovered using CSDA and aspartate testing) Shows interaction between PRs and bipolars Higher threshold and saturation than B-wave
41
What are the characteristics of the B-wave?
Positive potential (sum of PIII and PII) Originates from ON-bipolars (eliminated by aspartate and APB)
42
What synapse does aspartate block?
PR to bipolar
43
What is the Muller cell hypothesis?
B-wave is generated by Muller cells due to K+ ions being pushed into extracellular space by ON-bipolars
44
What is the ON-bipolar hypothesis?
ON-bipolars directly resonsible for B-wave because B-wave isn't eliminated by Barium (blocks Muller cells)
45
What is the current theory about B-wave origin?
ON-bipolars directly or indirectly responsible, some input from PRs
46
What are the characteristics of the C-wave?
Positive potential 2-10 second latency Only seen in scotopic conditions with bright flash Originates from RPE - closure of cation channels in PR OS reduces extracellular K+ (destruction of RPE eliminates) Can't record in humans
47
What are the characteristics of the D-wave?
Originates from cone-OFF pathway (OFF-bipolars) Only seen in photopic conditions with bright and long stimulus
48
What are the characteristics of Oscillatory Potentials?
Only seen in mesopic conditions Wavelets on rising edge of B-wave Bandpass filter used for analyse (100-150hz) 20ms latency Separated by ~7ms Originates from IPL (amacrine and GC)
49
What can OPs help to assess?
Retinal Ischaemia - DR
50
What are the characteristics of the Scotopic Threshold Response (STR)?
Negative potential Dim flash in darkness Increases in size with brighter light Originates from amacrine/GCs
51
What are the characteristics of the Photopic Negative Response (PNR)?
Negative wave after B-wave Likely originates from GCs - reduced in glaucoma
52
What cells does the pattern ERG detect signals from?
RGCs PRs
53
What does the P50 show in the pattern ERG?
Light response from PRs (Retinal Illuminance Response/RIR) Outer retina responses to illuminance changes
54
What does the N95 show in the pattern ERG?
Pattern response from RGCs (Pattern specific response/PSR) Sum of all central RGC responses.
55
What is the ISCEV standard for pattern ERG?
DTL or gold foil electrode Skin electrodes must have a resistance of <5kOhms Checkerboard pattern must subtend 12-18 degrees of the retina Checks in the pattern must be 40 min of arc Contrast must be >80% Luminance must be 80cdsm-2 1-3hz reversal Bandwidth filter of 1-100hz must be used >100 sweeps must be done
56
Why is there a specific size that the checks in the pattern ERG must be?
To obtain the biggest response from the RGC cells. If it were bigger, the response would be smaller due to the lower spatial frequency.
57
What can the pattern ERG be used for clinically?
Assessment of central retinal function Can differentiate between outer retinal disease and glaucoma/ON damage
58
What is the difference on the pattern ERG between outer retinal disease and glaucoma/ON damage?
Outer retinal disease: P50 and N95 reduce by the same amount Glaucoma/ON damage: only N95 reduces (due to central damage only)
59
What is the size of the area assessed by the pattern ERG?
Less than 20 degrees
60
Which element of the pattern ERG is not visible on everyone?
N35
61
What is required for the pattern ERG and how is this achieved?
Clear image Achieved by using refractive correction, no dilation and not using a CL electrode

Investigative Optometry and Case Studies (4 decks)

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