ASCRS ♦ ASOA Symposium & Congress

Technicians & Nurses Program

May 6-10, 2016 – New Orleans

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SU-18 Use of Electroretinography (ERG )

and Visual Evoked Potential (VEP) in Ophthalmic Practice

May 9, 2016 3:30 pm

Room R08-R09

Instructor: April Anderson, COA Disclosure: Clinical Application Specialist, Diopsys, Inc. Faculty: Joanne L. Yawn, COT William E. Sponsel, MD Course Level: Intermediate

This lecture is an intermediate course for use of commonly used visual electrophysiology (EP) tests:

• Electroretinography (ERG) • Visual evoked potential (VEP)

Course Description: Objective:

• Learn different testing stimuli for different diseases (flash and pattern)

• Produce quality tests for physician

decision making

Summary From Basic Introduction of Visual Electrophysiology:

1. WHAT: Use of Visual Electrophysiology is accepted. 2. WHO: by Vision Specialists. 3. WHICH: Vision Specialists order and direct the performance of the most specific EP test, using ISCEV and current evidence as references. 4. WHY: because visual function is an important component for diagnosis and treatment. 5. WHEN: When patients or certain subclinical disorders require alternative or adjunctive testing. 6. HOW: EP is performed by ophthalmic technicians and assistants based on physician direction.

Visual Electrophysiology Purpose:

Measures the electrical signals in the visual pathway

• Quantifies (measures ) strength and speed of visual signal

• Objectively – (not based on patient cognitive response)

• For in-depth, comparative data for physician’s medical decision

• It provides information about visual function that

no other tests can provide

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http://www.aviva.co.uk/health-insurance/home-of-health/medical-centre/medical-encyclopedia/entry/test-visual-evoked-responses/

Basic Visual Electrophysiology Equipment

1. Electrodes are applied to the patient (no electricity goes to the patient)

2. Electrodes are connected to wires to a signal amplifier

4. The computer receives and analyzes the electrical response generated by the patient

3. The patient focuses on the stimulus screen

5. A report containing wave forms is generated by the computer for physician interpretation

Tests measure different areas in the

visual pathway 1. Electroretinogram

2. Visual Evoked Potential

“ERG” measures retinal function

“VEP” measures the function of the entire visual pathway to the visual cortex (brain)

Areas in the Visual Pathway

• RETINA

• OPTIC NERVE

• MIDLINE CHIASM

• PERICHIASMAL

• LATERAL GENICULATE

• OPTIC RADIATIONS

• OCCIPITAL LOBE

ERG

VEP

To differentiate and monitor ophthalmic from other causes:

Neurological Infectious Vascular Endocrine Neoplastic Autoimmune Trauma Toxic

WHICH test is needed?

VEP

OR for vision disorders that affect: Optic nerve or pathway

Glaucoma Maculopathies Inherited retinopathies Drug toxicities

WHICH test is needed?

ERG

Clarify, locate, quantify, monitor retinal function:

WHEN is Supplemental EP needed? (under what circumstances))

Alternative (in place of) E.g. when standard tests are equivocal or cannot be performed by patient

Adjunctive (in addition to ) E.g. when standard test recommendations do not provide the level of information for diagnosis and treatment, (for more in-depth analysis)

Supplemental (in addition to)

or

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Adjunctive (in addition to):

Adjunctive (for more in-depth assessment)

Equivocal Diagnoses:

c Confirm or rule out differential diagnoses

c Patient complaints inconsistent with other test results

c Other test results questionable or borderline

c Multiple risks factors for subclinical/asymptomatic disorder

Location:

c VEP for optic nerve or retrobulbar dysfunction

c ERG to isolate dysfunction, ERG used after abnormal VEP

Progression:

c To quantitate level of severity or progression

c To track treatment efficacy for changes to care plan

Questionable, inconsistent, atypical, greater risk

Where is the dysfunction?

Measure at a deeper level for earlier treatment

Example: Adjunctive test for

Concomitant Disorders: Flicker Flash ERG for Cataract

When dilated ophthalmoscopy can’t get behind opacity

Test helps confirm retinal dysfunction vs. visual obstruction from cataract

Flicker flash permeates the opacity

Example: Adjunctive for Equivocal

Diagnostic inconsistencies

Complaints, test results not adding

up

Objective function evaluation

Provides comparative data for

decision making

pERG is performed Abnormal VEP prompts an pERG

Example: Adjunctive to Locate Questionable Dysfunction and Comorbidities

Abnormal VEP pERG is normal

Dysfunction is retrobulbar

pERG is Abnormal

Isolated dysfunction to the retina

Example: Adjunctive/Monitor Dysfunction

Monitor Vascular (Diabetic) or Macular (Retinal) Dysfunction

Non-compliant Diabetic

Better or Worse Alter treatment

Alternative: (For subclinical, below the surface of clinical

detection, in place of)

Alternative Function Test (to acuity, field or contrast)

Other Functional Test Limitations:

c High false positive (other) test result

c Unreliable (other) test result

Patient Limitations:

c Unable to coop. or understand other procedures

c Physical limitations

c Cognitive limitations

c Preverbal (pediatrics)

c Unable to communicate

When psychophysical acuity, field or contrast testing is questionable

Stroke, paralysis, learning disabled, preverbal, language barriers

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Example: Alternative for Visual Field Pattern ERG for Glaucoma Suspect with Low Test

Reliability on Visual Field Test

Example: Alternative for Acuity VEP as an alternative for Acuity Testing (Amblyopia)

Physician Developed Testing Protocols

• Questionable findings

• Multiple risk factors

• Locate dysfunction

• Monitor for functional changes for treatment

Physician

• Unable to perform or unreliable function, e.g.

• pERG for glaucoma suspects

• Flicker ffERG for maculopathies

• pVEP for amblyopia

Technician

1. Based on Medical Necessity

• to improve structure or function

2. Only known Contraindication • if history of seizures • Doctor’s decision if test result is more valuable to patient

care than risk)

3. When ordering ERGs with intraocular ERG electrode placements, consider patient tolerance. 4. Physician documents test reason in chart/EMR and orders test.

• Specify test and stimulus

For Physician Consideration and Order:

FLASH

Selection of Stimuli for ERG or VEP

Retinal Dystrophies Vascular/Diabetes Opacities Traumas Questionable Vision or Vision Loss Albinism Toxicities Nutritional Eye Diseases

http://www.iscev.org/standards/proceduresguide.html

Light (Flash) Stimuli Evoke Responses from Different Areas in the Retina

Selection of stimuli evoke a response from different areas in the retina: 1. Different levels of brightness

or luminance, 2. Speed or presentation of the

flash or flicker 3. Dark and light adaptation

http://www.iscev.org/standards/pdfs/ISCEV-VEP-Standard-2016draft%202015-12-17.pdf http://webvision.med.utah.edu/book/electrophysiology/the-

electroretinogram-clinical-applications/

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ERG and VEP Light (Flash) Stimulus Source

http://www.iscev.org/standards/pdfs/ISCEV-ERG-Standard-2014draft-v4.7.pdf

Ganzfeld Mini-Ganzfeld

PATTERNS

Patterns Stimulate the Ganglion Cells of the Retina

Vascular/Diabetes Opacities Traumas Retrobulbar Neuritis Questionable Vision or Vision Loss Albinism Toxicities Nutritional Eye Diseases Glaucoma Suspected Intracranial Lesions

http://www.iscev.org/standards/proceduresguide.html

3. Contrasts

Pattern Stimuli varies for ERG and VEP

1. Patterns/Speed

2. Check size (acuity) with different “Spatial Frequencies”

64 X 64 16 X 16

High Contrast Stimulates Parvo Cells of Retina for Central Vision

and Acuity (>80%)

Low Contrast Stimulates

Magno Cells of Retina for early detection of

field loss

Checkerboard Bars

14m

Example: Difference between Function and Structure

(to see how well they are functioning, strong or weak)

OCT measures Retinal Nerve Fiber Layer (RNFL) structure after cell death

pERG measures dysfunction earlier than observable structural change

Pattern Stimulus

The Technician’s Role

a. Device preparation • Follow physician instructions and manufacturer operator

manual • Enter patient information • Set up for correct test settings (fixed protocol vs. physician

specific directions for test type, OD/OS, stimuli)

b. Patient preparation • Best Corrected Visual Acuity (BCVA) • Not dilated • Place patient at recommended distance from computer

screen • Explain to patient test measures electrical current from

their visual pathway (No electricity goes to the patient) • Direct patient to focus on center of screen, ok to blink, eye

lubrication prn

The Technician’s Role (continued)

c. Electrode Application • Different placements for different test, VEP vs.

ERG • Cleanse area • Apply conductive paste • Apply electrodes • Check for good signal (conductivity/impedance)

d. Confirm prescribed stimuli • OD-OS-OU • Time • Pattern • Size • Contrast

e. Run test for a reliable result • Monitor patient for focus • Minimize interferences or artifacts (bad results from e.g.

excessive blinking, poor connection, microwave, etc.) • Finalize test report (print or export to EMR) for physician

review

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The Technician’s Role in the Standard ERG

Electrode (Sensor) Placement Ground

Reference Active

• Test one eye at a time using same protocol

• Occluded eye becomes reference

• Test the other eye

Different ERG Electrodes (Sensors)

Based on Manufacturer Recommendations Consider patient tolerance for invasive electrodes

Transcutaneous Corneal or DTL

Performing the ERG Test Flow

• Electrodes are connected by wire to an amplifier and

computer

• Test is run

• Computer analyzes patient response

• Report to doctor

Transient (Slower) Pattern ERG produces the N35-P50-N95 Complex

Source: http://www.iscev.org/standards/pdfs/ISCEV-PERG-Standard-2013.pdf

• At low temporal frequencies (\6 reversals per second (rps)…”

• Amplitude – measured on Vertical Axis between N35 and P50 (usually at 2.0 and 8.0 uV)

• Time – “Peak Time or Implicit time” measured from N35 to P50 (about 45-60ms) on Horizontal Axis

Faster Stimulus pERG (Steady-state) creates different wave form

• Means faster pattern reversal stimulus - “At higher temporal

frequencies, that is, above 10 rps (5

Hz), the successive waveforms overlap and a ‘‘steady-state’’

PERG is evoked.”

• Receptive to early glaucoma

Steady-state pERG Example

AFTER Normal Functioning Ganglion Cell

BEFORE Ganglion Cell Under Stress (OHT)

Abnormal pERG showed RGC dysfunction in early glaucoma

After lowering IOP, normal RGC function was restored

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Flash Flicker ERG

http://webvision.med.utah.edu/book/electrophysiology/the-electroretinogram-clinical-applications/

• Use light to get behind opacities (cataracts)

• Manage concomitant retinal dysfunction

• Set the right expectation for patient surgical outcome

Reference Ground Active

Now VEP Sensor Placement Made Simple

Testing one eye at a time

Visual Evoked Potential (VEP) Example

Visual – patient observes a visual stimulus Evoked – generates electrical energy at the retina Potential – measure the electrical activity in the visual cortex.

Performing the Test

Objectively measures the function of the entire vision system

“Transient” (speed of reversing pattern) is slower than Steady-state

VEP

• Stimulation at a relatively low rate (up to 4/s) will

produce “transient” VEP

• Faster pattern reversal is called Steady-state VEP

and produces a different

wave form

Guideline 9B: Guidelines on Visual Evoked Potentials1 RECOMMENDED STANDARDS FOR VISUAL EVOKED POTENTIALS https://www.acns.org/pdf/guidelines/Guideline-9B.pdf

For Physician Interpretation: Pattern Transient VEP (used most frequently) records the

N75-P100-N135 Complex

• N75-P100-N135 Complex • N75: Negative Pulse

around 75ms

• P100: Positive pulse

around 100ms

• N135: Negative pulse

around 135ms

ISCEV standard for clinical visual evoked potentials (2009 update)

Transient Pattern VEP Example

• Compare normal wave form to abnormal wave form

• Compare function of OD vs. OS.

Normal Abnormal

OD

OS

VS.

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How to read the wave form Amplitude (strength)is measured between

N75 and P100

• Y or Vertical Axis

• Measured in microvolts (μv)

• Delta measurement from N75 to P100

o NOT FROM ZERO

• Typical conditions that may cause a decreased amplitude

(E.G. refractive error, cataracts, corneal opacities, obstructions (ptosis)

Transient Pattern VEP Latency (Time, Speed) results are always compared to

P100, where the peak occurs in relation to the horizontal axis

• X or Horizontal Axis

• Shows where the P100 falls in time

• Measured in milliseconds (ms)

• Typical Conditions that may cause a delay in latency

o E.g. Optic Neuritis, Amblyopia, Traumatic Brain Injuries, Glaucoma, etc.

Pattern VEP Report Example for Amblyopia

• Used to detect differences in amplitude (strength) and latency (speed of the visual signal) in each eye

• OS signal is weaker and slower than OD • Repeat test after occlusion therapy for treatment efficacy

Amplitude Latency

OD

OS

OD

OS

OS OS

P100 Delay

Transient Pattern VEP Multiple

Sclerosis Example

Actual timing is delayed

Expected P100 timing

• Test based on patient history, chief complaint and other test results

• Evaluate both eyes for comparison

• Minor amplitude difference

• Latency abnormalities consistent with optic nerve dysfunction

• Refer to neurologist • Compare VEP test result

to subsequent VEP testing to monitor efficacy of treatment or worsening condition.

Summary:

• ERG for concerns of the

• Adjunctive – for subclinical disorders (below the surface), equivocal

• Stimulus varies by

• Consult your Operators Manual for desired

Optic Nerve to the Brain

Retina

“in addition to”

“in place of”

Flash or Pattern

Test and Stimuli

wave forms and electrodes

• Patient setup is the key

• VEP for concerns of the

• Alternative – when patients can’t perform reliably on standard tests

• Test results (wave forms) vary by

Questions?

THANK YOU!

April Anderson

(859) 806-1800