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Learn · Connect · Succeed
JCAHPO Regional Meetings
2017
4/27/2017
1
CL/MED-15 Use of Electroretinography (ERG ) and
Visual Evoked Potential (VEP) in Ophthalmic Practice
May 8, 2017 10:30 amRoom 502A
Instructor: April Anderson, CCOA
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
4/27/2017
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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:
NeurologicalInfectiousVascularEndocrineNeoplasticAutoimmuneTraumaToxic
WHICH test is needed?
VEP
OR for vision disorders that affect:
Optic nerve or pathway
GlaucomaMaculopathiesInherited retinopathiesDrug 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 cannotbe 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 confirmretinal dysfunction vs. visual obstructionfrom cataract
Flicker flash permeatesthe opacity
Example: Adjunctive for Equivocal Diagnostic inconsistencies
Complaints, test results not adding
up
Objective function evaluation
Provides comparative data for
decision making
pERG is performedAbnormal 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
cUnreliable (other) test result
Patient Limitations:
c Unable to coop. or understand other procedures
cPhysical limitations
cCognitive 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 AcuityVEP 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 DystrophiesVascular/DiabetesOpacitiesTraumasQuestionable Vision or Vision LossAlbinismToxicitiesNutritional 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/
4/27/2017
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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/DiabetesOpacitiesTraumasRetrobulbar NeuritisQuestionable Vision or Vision LossAlbinismToxicitiesNutritional Eye DiseasesGlaucomaSuspected 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 6416 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
4/27/2017
6
The Technician’s Role in the Standard ERG
Electrode (Sensor) Placement Ground
ReferenceActive
• Test one eye at a timeusing same protocol
• Occluded eye becomesreference
• Test the other eye
Different ERG Electrodes (Sensors)
Based on Manufacturer RecommendationsConsider 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
BEFOREGanglion Cell Under Stress (OHT)
Abnormal pERG showed RGC dysfunction in early glaucoma
After lowering IOP, normal RGC function was restored
4/27/2017
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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 stimulusEvoked – generates electrical energy at the retinaPotential – 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 formAmplitude (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 VEPLatency (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
OSOS
P100Delay
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