Final: Electroretinography Flashcards
What does the electroretinograph measure?
Measures the change in potential of the eye when the retina is stimulated with a flash of light
What is the electroretinograph (ERG) used for?
It is used primarily to diagnose retinal degeneration.
Where are the electrodes placed on an ERG?
One on the cornea and one on the skin next to the eye
What are fast oscillations generated by?
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.
What are fast oscillations very sensitive to in normal subjects?
Changes in blood glucose levels
What is a fast oscillation (FO)?
rapid decrease in the standing potential of the eye that occurs about 45 seconds to 1 minute after the onset of light.
What is a slow oscillation (SO)?
slow increase in the standing potential of the eye that peaks about 12 minutes after the onset of light.
What are researchers and clinicians referring to when they talk about the ERG?
Usually refer to the changes that happen within the first few seconds of a flash of light.
What are the most important components of an ERG?
The a and b waves in the beginning of the reading.
What is the PI ERG component according to Granit?
A slow, “cornea-positive” response, was first to disappear.
What is the P I ERG component according to Granit?
A slow, “cornea-positive” response, was first to disappear.
What is the P II ERG component according to Granit?
an earlier “cornea-positive response, disappeared second.
What is the P III ERG component according to Granit?
the “cornea-negative” response that remains when P I and P II are extinguished. (With further anesthesia this also disappears.)
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 _______.
mGluR6; ON; hyperpolarize; glutamate
What are the 4 main types of ERG electrodes?
1) Burian-Allen Electrode
2) JET Electrode
3) Gold Foil Electrode
4) DTL Fiber Electrode
What electrode is typically used for clinical purposes?
Burian-Allen electrode
Skin ERG is _____ accurate than corneal ERG.
less
What is the standard procedure for a dark adapted ERG?
- 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.
As light level of flash increases, the standard ERG response is __________.
larger
Describe the graph of a standard ERG. (x-axis, y-axis, a wave, b wave, c wave)
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
What are 3 measurements of interest on an ERG?
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
When we evaluate an ERG, what two parameters do we look at? What do we want to know when viewing the graph.
Amplitude and implicit time.
We want to know time between when the stimulus flashed and when the A-wave started to form.
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.
False; typically a patient that is dark-adapted would have a higher response.
Describe the term dual retina and what it has to do with ERG.
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.
