Electrophysiology Flashcards
An ERG has 4 main waves. What are they, are they + or - and what do they indicate
- a wave = negative = photoreceptrs
- b wave = positive = ON bipolar cells/mueller cells
- c wave = positive = RPE and rod function
- d wave = ? = OFF bipolar cells
Oscillatory Potentials (OPs) are indicative of what type of activity in what location?
Amacrine cell active in IPL
Where are the 3 electrodes placed for an ERG?
- Cornea (active)
- Earlobe or Forehead (ground)
- Forehead or temple (reference)
If a patient has a delay in the B-wave and super-normal response, what disease could it be?
- Early Siderosis Bulbi
If a patient has a delay in the B-wave with subnormal response, this means what?
indicates large area of retina is not functioning
A subnormal b-wave is indicative of what diseases?
- Early RP
- Chloroquine & Quinine Toxicity
- Partial RD
- Systemic (Vit A def, hyperthyroidism, anemia)
What diseases are associated with complete absence of response?
- Advanced cases of RP
- Complete RD
- Leber’s
Abnormalities of the oscillatory potential (OPs) are due to what?
Ischemic retinopathy
This type of ERG is only impacted with widespread retinal involvement?
Full Field ERG
What type of ERG is best used if patient has poor scotopic threshold on dark adaptation testing?
Full Field ERG
This type of ERG is best used to detect damage in a localized area of the retina (central or peripheral).
Focal ERG
This type of ERG is best used for macular disease and helps distinguish POOR VA due to macular disease or ON disease.
Pattern ERG
What wave on the pattern ERG is the initial corneal positive response and represents macular function?
P50 wave
What wave is the immediate corneal negative response and represents ganglion cell function?
N95 wave
This ERG looks at the central 40 to 50 degrees of retina; evaluates macula function and areas of concern in central retina.
Multi-focal ERG
On a multi-focal ERG, we’ll see small amplitudes in what 2 people?
- Elderly
2. Highly myopic eye
On an EOG, the cornea is ______ and the retina is _____.
- cornea is positive
- retina is negative
What is the continuous resting potential of the retina measured by the EOG?
- 6mV
For the arden ration, what are the numbers for normal and abnormal? (light peak/dark trough)
- normal = 2.0>
- abnormal = <1.8
An EOG is great for diagnosing what disease?
- Vitteliform Dystrophy (Best’s disease)
What is the only test that measures visual cortical activity by determining the integrity of the visual pathway from the retina to visual cortex?
VEP: Visual Evoked Potential
The VEP reflects activity mainly from what degree of VF?
central 10 degrees
Where are the 3 electrodes placed for a VEP?
- Occipital region - active
- Top of forehead/earlobe - ground
- forehead/top of head - reference
Which VEP is used clinically and allows the brain to return to baseline in between flashes
Transient VEP - has low temporal frequency
Which VEP is used when poor VA, media opacities or poor fixation is present?
Flash VEP
Which VEP will be abnormal in an amblyopic patient?
Pattern VEP
What 2 VEPs will be abnormal in an MS patient?
Flash and Pattern VEP
Which two tests will be abnormal in a macular lesion?
- Multi-focal ERG
2. Pattern VEP
What two tests will be abnormal in a RP patient?
EOG and ERG
Which is longer: implicit time or latency?
Implicit time
When separating the waves, which wave is the smallest and occurs first?
photopic a wave (ap)
We are doing an ERG and light adapt the eye first. What type of response will you see?
Cone only response
In order to maximize the size of the photopic response of the ERG, what wavelength would you use?
550nm
When separating the waves, which wave is the largest?
Scotopic b wave (bs)
Why does the ERG represent mid-peripheral and peripheral retina more than central?
Looks at the distribution of PRs throughout the retina
The b wave amplitude is larger for who?
Women (slightly)
