Visual And Ocular Electrodiagnosis

Question 1

What are electrodiagnostics for

Answer 1

• confirm normal functional status
• testing infants and unresponsive patients
• monitor for development of drug toxicity
• detect a sub-clinical disease
• detect early functional loss ins a progressive disease
• detect carrier state disease
• discriminate level of deficit
• monitor progression/reolsution of condition

Question 2

Larger potentials you can measure in the human body

Answer 2

Electrooculogram

6miliVolts

Question 3

ERG potential

Answer 3

Larger potential but less than EOG and ECG

Question 4

What kind of potentials do pERG, VEP, and mfERG

Answer 4

VERY small

Question 5

Voltage of eye

Answer 5

10-30mV from front to back of the eye

Question 6

In an EOG, when the eye rotates between a set of electrodes

Answer 6

It’s like the rotation of a generator that produces a sinusoidal change in voltage that can be measured

Question 7

The voltage measured in the EOG

Answer 7

The voltage produced by the eye movement is though to emanate from the rod system but is abnormal primarily in RPE disease

Question 8

Early form of visual recording

Answer 8

EOG

Question 9

Which is more common EOG or VEP/ERG

Answer 9

VEP/ERG

Question 10

Measuring the EOG

Answer 10

• place two electrodes, one on either side of the eye
• patient moves the eyes on command usually inside of a ganzfeld under both dark adapted and light adapted conditions
• there is a lower dipole voltage under dark adapted vs light adapted conditions
• called the “light rise” of EOG
• the ratio between the light and dark adapted voltages is called the Arden ratio which is normal between 1.65-1.80

Question 11

Arden ratio

Answer 11

The ratio between the light and dark adapted voltages in an EOG

Question 12

What is considered a good Arden ratio

Answer 12

1.65-1.80

Question 13

Reason the ganzfeld is bigger than the FOV

Answer 13

To adapt the rest of the retina

Question 14

EOG in Best’s doses (autosomal dominant vitiliform maculopathy)

Answer 14

Will have a normal ERG but not a normal EOG.

• referred to as “fried egg” macular appearance
• do not get a light rise in light adaptation

Question 15

Diseases in which the EOG can be abnormal

Answer 15

Bests 
Stargardt 
Pattern dystrophies
RP
Rod/cone dystrophies
Oguchi disease 
Fundus albipunctatus 
Choroidemia 
Gyrate atrophy

Question 16

How the ERG works

Answer 16

• arises from a flash light stimulus that cases a dynamic change in the measured voltage (1Mv) from the eye
• unlike the standing potential of the EOG, the ERG helps discriminate the functionality of more layers than just the RPE

Question 17

A wave in ERG

Answer 17

Arises from the photoreceptors

Question 18

B wave in ERG

Answer 18

Arises from bipolar layer and the depolarization of the mueller cells

Question 19

Oscillatory potentials in ERG

Answer 19

Represent “ringing” in the neural transmission at the amacrine cell layer

Question 20

C wave for ERG

Answer 20

RPE

Question 21

Mueller cells

Answer 21

Glial cells

Absorb the depolarization of the neurons

Question 22

Full field ERG

Answer 22

• full field ERG technique produced a “robust” measure of retinal function because it seeks to maximally stimulate almost all photoreceptor simultaneously
• uses a ganzfeld to integrate responses over entire retina
• patients frequency dilated
• not as useful for maculopathies because of small area of retina affected
• better for wide area diseases

Question 23

Full field ERG depends on stimulus conditions

Answer 23

By controlling the stimulus parameters, and the patients state of adaption, the ffERG allows the clinical to see the responses of the rod vs cone system

Question 24

Normal sequence of ERG stimuli

Answer 24

Things get brighter and as they get brighter, things get faster

Question 25

FfERG in RP

Answer 25

Not much activity

Question 26

Scotopic ERG

Answer 26

- dark adapted state - ganzfeld - patient dilated - dim blue light stimulus limits response to rods only - dark adapted recording of dim red stimulus includes some cone as well as rod response - gradually increasing levels of white light give stronger and stronger ERGtraces - note that with increasing stimulus intensity, the a-wave, and b-wave amps increase and their peaks move to earlier time course (latency of implicit time)

Question 27

When going from 30hz-60hz

Answer 27

Actually goes down, instead of going up like you think | -this is the flicker fusion frequency cut off

Question 28

Recap of ffERG

Answer 28

-changing patient adaptation and stimulus parameters leads to differential ERG traces that give us the ability to tease apart the functionality of the various component cells in the retina

Question 29

FfERG importance

Answer 29

An integrated look at the entire function of the retina layers and therefore looks best at problems like RP that affect entire classes of cells - not ideal for focal lesions such as maculopathy - can be helpful in the differentiation of and progress monitoring of a wide variety of retina diseases and hereditary conditions