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Visual Sensation and Perception > Final: Electroretinography > Flashcards

Final: Electroretinography Flashcards

1
Q

What does the electroretinograph measure?

A

Measures the change in potential of the eye when the retina is stimulated with a flash of light

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2
Q

What is the electroretinograph (ERG) used for?

A

It is used primarily to diagnose retinal degeneration.

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3
Q

Where are the electrodes placed on an ERG?

A

One on the cornea and one on the skin next to the eye

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4
Q

What are fast oscillations generated by?

A

They are generated by a light induced decrease in chloride ion concentration within the RPE and the accompanying hyperpolarization of
the basal membrane of the RPE.

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5
Q

What are fast oscillations very sensitive to in normal subjects?

A

Changes in blood glucose levels

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6
Q

What is a fast oscillation (FO)?

A

rapid decrease in the standing potential of the eye that occurs about 45 seconds to 1 minute after the onset of light.

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7
Q

What is a slow oscillation (SO)?

A

slow increase in the standing potential of the eye that peaks about 12 minutes after the onset of light.

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8
Q

What are researchers and clinicians referring to when they talk about the ERG?

A

Usually refer to the changes that happen within the first few seconds of a flash of light.

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9
Q

What are the most important components of an ERG?

A

The a and b waves in the beginning of the reading.

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10
Q

What is the PI ERG component according to Granit?

A

A slow, “cornea-positive” response, was first to disappear.

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10
Q

What is the P I ERG component according to Granit?

A

A slow, “cornea-positive” response, was first to disappear.

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11
Q

What is the P II ERG component according to Granit?

A

an earlier “cornea-positive response, disappeared second.

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12
Q

What is the P III ERG component according to Granit?

A

the “cornea-negative” response that remains when P I and P II are extinguished. (With further anesthesia this also disappears.)

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13
Q

In the mature retina APB binds with ______ receptors expressed by ___ cone bipolar and rod bipolar cells, which _________ these retinal interneurons and blocks their release of _______.

A

mGluR6; ON; hyperpolarize; glutamate

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14
Q

What are the 4 main types of ERG electrodes?

A

1) Burian-Allen Electrode
2) JET Electrode
3) Gold Foil Electrode
4) DTL Fiber Electrode

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15
Q

What electrode is typically used for clinical purposes?

A

Burian-Allen electrode

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16
Q

Skin ERG is _____ accurate than corneal ERG.

A

less

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17
Q

What is the standard procedure for a dark adapted ERG?

A
  • Dark adapt 35-40 min
  • Anesthetize subjects cornea (proparacaine)
  • Dilate pupil (tropicamide & phenylephrine)
  • Attach electrodes
  • Retina illuminated with different wavelengths, intensities, and rates of flashed light stimuli.
  • The electric responses are obtained by the electrode and then analyzed by computer.
  • If light-adapted responses are to be obtained, these are done after the dark-adapted responses.
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18
Q

As light level of flash increases, the standard ERG response is __________.

A

larger

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19
Q

Describe the graph of a standard ERG. (x-axis, y-axis, a wave, b wave, c wave)

A

X-axis: time in seconds
Y-axis: Retinal response in microvolts

A-wave:

  • negative-going (cornea-negative)
  • rods & cones ‘receptor potential’’
  • light-induced photoreceptor activity (i.e., change in dark current)

B-wave:
positive-going;
largest component of diffuse flash ERG;’
ON Bipolar cells, with some Müller cell contribution

C-wave:

  • positive-going; slower
  • 2 sub-components: smaller negative, neural retina larger positive, RPE
  • Caused by light-evoked decrease in [K+} in subretinal space
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20
Q

What are 3 measurements of interest on an ERG?

A

1) Amplitude (in microvolts) - height of wave reflects magnitude of the voltage change
2) Implicit Time (in milliseconds) - time between onset of the flash and the peak of the wave.
3) Latency - The time between stimulus onset and beginning of a-wave

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21
Q

When we evaluate an ERG, what two parameters do we look at? What do we want to know when viewing the graph.

A

Amplitude and implicit time.

We want to know time between when the stimulus flashed and when the A-wave started to form.

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22
Q

True or false:
The ERG response for a light-adapted patient is going the be higher than what it would be if the patient was dark-adapted.

A

False; typically a patient that is dark-adapted would have a higher response.

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23
Q

Describe the term dual retina and what it has to do with ERG.

A

Dual retina means that we have 2 types of photoreceptors that activate after the stimulus is present. Since we have more rods, the rod component will contribute more the graph than the cone component.

24
Q

What are 4 types of ERGs?

A

1) Diffuse flash
2) Focal (fERG)
3) Multifocal (mfERG)
4) Pattern (PERG)

25
Q

What type of ERG is the standard ERG? Describe it.

A

Diffuse Flash:

  • Can be applied to a dark- or light-adapted eye
  • “standard” (white)
  • works for scotopic
  • works for photopic system, usually flicker
  • scotopic balanced
26
Q

What is the type of ERG that you can direct the light on an exact location on the retina?

A

Focal (fERG)

27
Q

If you ran an ERG for scotopic systems, is the patient dark or light adapted? What kind of flash would you present?

A

Patient would be dark adapted.

Flash should be single, dim, and blue.

28
Q

If you ran an ERG for photopic systems, is the patient dark or light adapted? What kind of flash would you present?

A

Light adapted function
Single, red flash
high frequency filter

29
Q

Why would you use a high frequency filter for an ERG test for photopic systems?

A

Rods can not recover quickly enough to produce a response so most of the response is due to the cones.

30
Q

Even though cone density is greatest
 at the fovea, ____ of the cones are located OUTSIDE of the FOVEA.

A

90%

31
Q

What is the ratio of rods to cones?

A

13 to 1

32
Q

What wave is missing during a scotopic ERG?

A

A-wave is missing.

33
Q

Is the b-wave larger or smaller during a scotopic ERG?

A

B-wave has a smaller amplitude.

34
Q

What can scotopic balancing be used for?

A

To characterize diseases that have a predilection for either rods or cones.

35
Q

The stimuli are said to be scotopically balanced if….

A

If a long-wavelength (red) light produces an ERG with the same amplitude as does a short-wavelength (blue) light in a dark-adapted conditions

36
Q

What is the importance of using scotopically balanced flashes? Give an example.

A

It can show irregularities between the responses of the two flashes. If they don’t have equal amplitudes, something may be wrong.

Example: If the red flash produces a response lower than the blue, it may represent a problem with the patients cones.

37
Q

What are the testing parameters for the Standard ERG?

A

Dark adapted subject
Single, Bright, White Flash (5 ms)
Mixture of photopic (cone) and scotopic (rod) response components

38
Q

What are the 6 standard ERG components?

A

1) Early Receptor Potential (ERP) – before a-wave
Photoreceptors (outer segments)

2) a-wave:
Photoreceptors
Separate waves for photopic & scotopic conditions.

3) Oscillatory Potentials (OPs)
Ascending limb of b-waves when generated with a bright flash.
IPL / (Amacrine Cells?)

4) b-wave
Bipolar & Müller cell origin
Separate ones for photopic & scotopic conditions.

5) Afterpotential
On descending limb of b-wave, where ERG goes below baseline voltage.

6) c-wave:
Retinal Pigment Epithelium (RPE)

39
Q

The a and b waves have ____ temporal frequency.

A

low

40
Q

If we filter out the a and b waves, it reveals the _____________.

A

oscillatory potentials

41
Q

How many major oscillatory potentials are there?

A

Up to 3 major oscillatory potentials followed by smaller ones

42
Q

What kind of filter is applied to the ERG? (high pass, low pass, or band pass)

A

High-pass

43
Q

Where are the “wavelets: coming from in the graph?

A

interplexiform layer (possibly amacrine cells)

44
Q

What may the patient have when their oscillatory potentials are irregular?

A

May have diabetic retinopathy, hypertensive retinopathy, central retinal artery and vein 
 occlusions.

45
Q

Oscillatory potentials are very sensitive to _______, so their attenuation in an
ERG in which the a and b waves are normal can be used as an
 indication of mild _______ in the _________.

A

ischemia; ischemia; inner retina

46
Q

What is the origin of oscillatory potential?

A

Origin is unknown

47
Q

What photoreceptors do we isolate when using flicker ERG?

A

Cones

48
Q

How do we record the Scotopic Threshold Response (STR)? What part of the retina do scientists believe this tests?

A
  • Fully Dark-Adapted Eye
  • Very Dim (Near-Threshold), Full-Field Flash
  • May test the proximal/inner retina from the Muller cells and amacrine cells.
49
Q

What clinical value does Scotopic Threshold Response show?

A

Can be shown to be affected with people who have juvenile X-Linked retinoschisis and early diabetic retinopathy

50
Q

What is focal ERG mostly used for?

A

Most often used for macular disorders but can be applied to any small area of the retina 
(~10 deg. diameter)

51
Q

How does a Multifocal ERG work?

A

It produces many stimuli across sections of the retina which causes those sections to produce their own response. Those values can be mapped out on a 3D graph.

52
Q

Describe pattern ERG.

A

Use JET, gold foil, or DTL fiber electrode
-Need clear optical path

Pattern (contrast) reversal stimulus
Response Origin
-Inner retina: mainly ganglion cells

53
Q

What is the clinical use for pattern ERG?

A

There are abnormal PERG in…
glaucoma
CRA occlusion
optic nerve trauma

54
Q

What component of the retina is the c-wave associated with?

A

Retinal pigment epithelium

55
Q

What component of the retina is the a-wave associated with?

A

Rods and cones

56
Q

What component of the retina is the b-wave associated with?

A

Muller cells

ON bipolar cells

57
Q

What component of the retina is the d-wave associated with?

A

OFF bipolar cells

58
Q

What component of the retina is the oscillatory potentials associated with?

A

amacrine cells

Visual Sensation and Perception (19 decks)

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