Lecture 10: Electrodiagnostic Testing: ERG & VEP

Question 1

what is a full field ERG? What are the 3 types of ERG

Answer 1

• mass response of the entire retina for rod or cone systems
• Photophic negative response (PhNR) - evaluates ganglion cell function
• Pattern ERG (pERG) - evaluates ganglion cell function
• Multifocal ERG (mfERG) - provides topographic mapping of central retina and function of cone system
• mass electrical repsonse of the retina to luminance stimulation

Question 2

What are the 2 main components of ERG?

Answer 2

• Scotopic (dark adapted response)
• Photopic (light adapted response)

Question 3

What is visual evoked potential (VEP)?

Answer 3

• function of primary visual pathway at cortical level
  
  • mfVEP

Question 4

What is EOG?

Answer 4

• electrooculogram - RPE function

Question 5

What are the 4 types of diopsy vision testing system and what do each of them assess for?

Answer 5

• ffERG - objectively evaluate cone & ganglion cell function
• mfERG - objectivley evaluating localized retinal function
• PERG - objectively evaluating ganglion cell function
• VEP - Protocols for objectively evaluating the function of the entire visual pathway

Question 6

Scotopic response: first positive b-wave noted is a pure __ response

Answer 6

ROD

(Scotopic response)

Question 7

Max response to first stimulation is most important in determining between ___ and ___ pathology

Answer 7

photoreceptors, inner layer pathology

(scotopic response)

Question 8

Negative a-wave assesses what?

Answer 8

photoreceptor function

Question 9

Postive b-wave assesses what?

Question 10

Photopic response: negative a-wave assesses what?

Answer 10

cone photoreceptors

Question 11

Scotopic response: Positive b-wave inner retinal function

Question 12

__ suppressed by flicker in photopic response

Answer 12

rods

Question 13

Negative a wave = ____ ; Negative b wave = _____ & _____

Answer 13

• photoreceptor response
• bipolar & mueller cells

Question 14

Oscillatory Potentials (OP)

Answer 14

• ​Inner retinal currents from amacrine cells
• Low amplitude wavelets superimposed on ascending B-wave

Question 15

What is PhNR? (Photopic negative response)

Answer 15

• slow negative component of B-wave of the CONE driven ffERG
• Originates from ganglion cell activity
• depends on intact RGC function

Question 16

Modest correlation between amplitude of PhNR & thickness of… ? (2)

Answer 16

• peripapillary RNFL
• Ganglion cell layer thickness within the macula

Question 17

Pattern ERG is generated by the ___ and shows ____.

Answer 17

macula; spatial frequency selectivity

Question 18

Pattern ERG - retinal response what stimulus?

Answer 18

structured stimulus - reversing black/white checkboard grating

Question 19

pattern ERG should always be read with ___ or __

Answer 19

ffERG or VEP

Question 20

Pattern ERG is affected by diseased confined to the __

Answer 20

macula

• will be normal in sever ROD-cone dystrophy with good central VA
• May diagnose diseases that affect only the macula

Question 21

___ is considered to be one of the best electrodiagnostic tolls for assessment of RGC function

Answer 21

PERG

Question 22

PERG provides a functional evaluation of the retina __ __ function and __ __ function.

Answer 22

macular cone; ganglion cell

Question 23

What are the 3 components of pattern ERG?

Answer 23

• Negative (N35)
• Positive (P50)
  
  • Some RGC component
• Negative (N95)
  
  • Large RGC component

Question 24

Which one is normal and which one is abnormal PERG?

Answer 24

Top normal

• there are glaucoma patients who have abnormal ERG
  
  • P95 amplitude reduction is most significant

Question 26

In monkeys with bilateral optic atrophy and loss of central RGCs (green trace), the PERG, particularly the \_\_ component, is substantially reduced while the full-field flash ERG remains normal.

Answer 26

N95

Question 27

What is mfERG

Answer 27

* Provides topographic mapping of the central retinal function for the cone system * Diameter of 40-50 degrees * Allows detection of focal changes in retinal function

Question 28

mfERG: Amplitude and implicit time of the \_\_component are most commonly used for analysis

Answer 28

P1

Question 29

**Pattern Visual Evoked Potential (pVEP)** waveform components include what? (3)

Answer 29

* N75 * P100 * Delay of latency of P100 indicates ON dysfunction involving axon (neuritis or demyelination) * Decrease in amplitude of P100 is usually due to atrophic changes * N135 * Changes to the pVEP allow clinicians to place defect at the optic nerve, but it is very general * We need more specifics for glaucoma... e.g. location within the optic nerve

Question 30

Complete the chart

Answer 30

Question 31

Drawback of electrodiagnostic testing

Answer 31

* Some tests are invasive (require electrodes on eye and eyelids) * Some tests are long (45 to 50 minutes) * Require consistent protocols and expert interpretation