Unit 3 - Electrophysiology Flashcards
When are electrophysiology tests indicated?
- Abnormal fundus
- Symptoms incompatible with signs
- Abnormal eye movements
- FH of genetic disease
Monitoring assessment of treatment
Outcome/safety data in clinical trials
What electrodes are used for retinal testing?
Corneal electrode as active
Surface electrode on outer canthus as reference
What test do you use to examine the photoreceptors and inner nuclear layer?
Full field ERG
What 5 tests make up the full field ERG protocol?
Dark adapted for 20 mins then:
1. DA0.01 flash: b wave only relates to rods
2. DA 3.0 flash: combined response of rods and cones but mainly rods.
3. DA 10.0 flash
Light adapted for 10 mins
4. 30HZ flicker: pure cone response
5. Single flash: gives a and b wave
Where does the a wave on a full field ERG come from?
Photoreceptors
Where does the b wave on an ERG come from ?
Bipolar cells
What tests are used congenital stationary night blindness?
On-Off full field ERG. b wave is produced from both on biopolar cells and off bipolar cells.
What test can be used to look at macula and retinal ganglion cell function?
Pattern ERG
What test does this come from? Where does the P50 and N95 signals come from?
Pattern ERG
P50 = 70% retinal ganglion cells from macula cones
N95 = retinal ganglion cells
Where does the EOG come from?
RPE
What test can be used to differentiate between Best’s disease and adult vitelliform disease?
EOG - light peak is reduced with Bestrophin gene involvement.
What is this and where does it come from?
VEP from optic nerve and chiasm
When would you use a three channel VEP rather than a single one?
Albinism (looking intracranial misrouting)
Chiasmal and retrochiasmal dysfunction
In a VEP what is measured in terms of the P100?
Timing and amplitude
When would the P100 wave be delayed in a VEP
MS,
