ERG + VEP Flashcards
List the 5 layers of retinal neurons, from caudal to rostral (order of activity)
1) Photoreceptors (rods and cones)
2) Horizontal cells
3) Bipolar cells
4) Amacrine cells
5) Retinal ganglion cells
- Photopic vision (daylight) is mediated by a)
- Scotopic vision (dim light) is medicated by b)
a) cones
b) rods
On mange des cones de crème glacée le jour
Cones
- a) mediate ____ vision.
- b) ____cone(s) per ganglion cells
- c) ____Se, ____acuity
- d) respond best to ____ frequency flashes
a) photopic (daylight)
b) as few as 1
c) Low Se, High acuity
d) High f
Rods
- a) mediate ____ vision.
- b) ____rod(s) per ganglion cells
- c) ____Se, ____acuity
- d) Respond best to ____ frequency flashes
a) Scotopic (dim light)
b) hundreds
c) high Se, Low acuity
d) low f
Note: rods and cones are DEPOLARIZED in the dark (release glutamate) due
ERG (flash)
Name the 3 major components of the ERG waveforms
a-wave
b-wave
Photic negative response (PhNR)
ffERG
What is a full field ERG (ffERG)
Summed response of the entire retina following uniform stimulation by a Ganzfeld bowl.
a mass response of the retina that has contributions from several retinal sources, summed throughout the retina. This is useful in diseases that have widespread retinal dysfunction
ERG (flash)
Origin and morphology of a-wave, b-wave and PhNR
- a-wave: Photoreceptors (mainly cones) - 1st downward (-, small) deflection
- b-wave: Bipolar neurons - 1st upward (+, large) deflection
- PhNR: Retinal ganglion neurons - 2nd downward (-, small) deflection
Slide 16
ERG
Define amplitude vs implicit times of waveforms (a, b)
amplitude:
a- wave: height from baseline to trough of a-wave
b-wave: height from trough of a-wave to peak of b-wave
implicit time: delay from flash delivery to trough of a-wave and peak of b-wave
Scotopic ERG
- The light stimulus is dim (low intensity), delivered q4 min for 20 minutes (time for dark adaptation)
- Targets rod activity.
- Useful to diagnose nyctalopia, SARD, PRA, cataracts, optic neuritis
PRA=progressive retinal atrophy
Photopic ERG
- hemeralopia
???
ERG (flicker)
Explain the flicker ERG principle
- Flash stimulus delivered at short intervals (~30 Hz)
- Retina does not have time to return to baseline electrical potentials
- ERG composed of b-waves only
- Progressive derease in response amplitude as flicker frequency increases, until the responses fuse
- Cones fuse at a higher frequency (35-75 Hz) than rods (10 Hz).
Slide 20
ERG
What is the consensus for healthy vs retinal disease based on a and b wave analysis?
Sum of A+B amplitudes =
< 100 mV = retinal disease
> 100 mV = no retinal disease
note: no ref values for a and b waves in vet med
ERG
Oscillatory potentials
- Small wavelets on the rising phase of b-wave
- Using high-intensity light stimulus
- (…)
more details slide 26-27
ERG
Pattern ERG
- Light stimulus = alternating checkerboard
- Evokes response from the ganglion cells
- Reflects inner retinal function
Rarely used in vet med
ERG
Multifocal ERG
slide 32, not important
