ERG/EOG Flashcards
What are the waves on ERG
a wave - response of photoreceptors
b wave - response of inner retinal elements - Muller, bipolar cells
What ERG change in CRAO
Decreased b wave amplitude
What is flicker response for?
Measuring cone responses as rods are unable to cycle quickly enough
What frequency of flicker-flash to isolate cone function
25Hz minimum
Rods can respond with rates up to 20Hz
Only cones at higher frequency with maximum of 70Hz
What does a normal ERG but sub-normal (reduced) light rise on EOG indicate
Best vitelliform dystrophy (AD)
ERG change if communication disrupted between photoreceptor and bipolar cells
B-wave selectively disrupted producing negative or inverted ERG
What are causes of negative ERG
(Inversion)
Congenital stationary night blindness
X-linked retinoschisis
CRAO
XRCC
What is the Pulfrich phenomenon
Delayed conduction in the demyelinated optic nerve (optic neuririts) and occurs where oscillating objects viewed binocularly moving in one plane appear to have a 3D movement
Delayed implicit time in VEP correlates to Pulfrich phenomenon
In dark adapted patient blue flash generates ERG with
Rod iput only
(below cone threshold in dark adapted state)
ERG a b c waves
a - photoreceptor
b - bipolar
c - RPE
What can be used as measure of VA in VEP
P100 amplitude
When checked pattern is reduced to a degree where it cannot be resolved, the cortical response subsides
