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Perception Block 12 > Visual And Ocular Electrodiagnosis > Flashcards

Visual And Ocular Electrodiagnosis Flashcards

1
Q

What are electrodiagnostics for

A
  • 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
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2
Q

Larger potentials you can measure in the human body

A

Electrooculogram

6miliVolts

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3
Q

ERG potential

A

Larger potential but less than EOG and ECG

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4
Q

What kind of potentials do pERG, VEP, and mfERG

A

VERY small

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5
Q

Voltage of eye

A

10-30mV from front to back of the eye

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6
Q

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

A

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

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7
Q

The voltage measured in the EOG

A

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

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8
Q

Early form of visual recording

A

EOG

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9
Q

Which is more common EOG or VEP/ERG

A

VEP/ERG

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10
Q

Measuring the EOG

A
  • 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
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11
Q

Arden ratio

A

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

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12
Q

What is considered a good Arden ratio

A

1.65-1.80

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13
Q

Reason the ganzfeld is bigger than the FOV

A

To adapt the rest of the retina

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14
Q

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

A

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
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15
Q

Diseases in which the EOG can be abnormal

A 
Bests 
Stargardt 
Pattern dystrophies
RP
Rod/cone dystrophies
Oguchi disease 
Fundus albipunctatus 
Choroidemia 
Gyrate atrophy
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16
Q

How the ERG works

A
  • 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
17
Q

A wave in ERG

A

Arises from the photoreceptors

18
Q

B wave in ERG

A

Arises from bipolar layer and the depolarization of the mueller cells

19
Q

Oscillatory potentials in ERG

A

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

20
Q

C wave for ERG

A

RPE

21
Q

Mueller cells

A

Glial cells

Absorb the depolarization of the neurons

22
Q

Full field ERG

A
  • 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
23
Q

Full field ERG depends on stimulus conditions

A

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

24
Q

Normal sequence of ERG stimuli

A

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

25
Q

FfERG in RP

A

Not much activity

26
Q

Scotopic ERG

A
  • 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)
27
Q

When going from 30hz-60hz

A

Actually goes down, instead of going up like you think

-this is the flicker fusion frequency cut off

28
Q

Recap of ffERG

A

-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

29
Q

FfERG importance

A

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

Perception Block 12 (6 decks)

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