ERG + VEP

Question 1

List the 5 layers of retinal neurons, from caudal to rostral (order of activity)

Answer 1

1) Photoreceptors (rods and cones)
2) Horizontal cells
3) Bipolar cells
4) Amacrine cells
5) Retinal ganglion cells

Question 2

• Photopic vision (daylight) is mediated by a)
• Scotopic vision (dim light) is medicated by b)

Answer 2

a) cones
b) rods

On mange des cones de crème glacée le jour

Question 3

Cones
- a) mediate ____ vision.
- b) ____cone(s) per ganglion cells
- c) ____Se, ____acuity
- d) respond best to ____ frequency flashes

Answer 3

a) photopic (daylight)
b) as few as 1
c) Low Se, High acuity
d) High f

Question 4

Rods
- a) mediate ____ vision.
- b) ____rod(s) per ganglion cells
- c) ____Se, ____acuity
- d) Respond best to ____ frequency flashes

Answer 4

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

Question 5

ERG (flash)

Name the 3 major components of the ERG waveforms

Answer 5

a-wave
b-wave
Photic negative response (PhNR)

Question 6

ffERG

What is a full field ERG (ffERG)

Answer 6

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

Question 7

ERG (flash)

Origin and morphology of a-wave, b-wave and PhNR

Answer 7

• 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

Question 8

ERG

Define amplitude vs implicit times of waveforms (a, b)

Answer 8

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

Question 9

Scotopic ERG

Answer 9

• 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

Question 10

Photopic ERG

Answer 10

• hemeralopia

???

Question 11

ERG (flicker)

Explain the flicker ERG principle

Answer 11

• 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

Question 12

ERG

What is the consensus for healthy vs retinal disease based on a and b wave analysis?

Answer 12

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

Question 13

ERG

Oscillatory potentials

Answer 13

• Small wavelets on the rising phase of b-wave
• Using high-intensity light stimulus
• (…)

more details slide 26-27

Question 14

ERG

Pattern ERG

Answer 14

• Light stimulus = alternating checkerboard
• Evokes response from the ganglion cells
• Reflects inner retinal function

Rarely used in vet med

Question 15

ERG

Multifocal ERG

Answer 15

slide 32, not important

Question 16

VEP

Visual Epoked Potentials (VEP) - general principle? Use?

Answer 16

Electrodes on the occipital lobe record info received in the visual cortex following light stimulation.

Useful to detect post-retinal lesions in the visual pathway

Is a polyphasic waveform

Question 17

VEP

What are the two types of VEP ?

Answer 17

• Flash-stimulated VEP (FVEP)
• Pattern-stimulated VEP (PVEP) - checkerboard

Question 18

VEP

in PVEP, a reduced peak amplitude of P100 is indicative of..

Answer 18

Reduced acuity

Slide 42

Question 19

VEP

What are the 3 electrodes of VEP

Answer 19

• Recording: Occipital lobe (Oz), called inion
• Reference: forehead (Fz), called nasion
• Ground: Vertex (Cz) or ear lobe