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ASCRS ♦ ASOA Symposium & Congress
Technicians & Nurses Program
May 6-10, 2016 – New Orleans
4/13/2016
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Basic Visual Electrophysiology in Ophthalmic Practice
An Introduction for Physicians, Ophthalmic Assistants and Technicians
Instructor: April Anderson, COA Disclosure: Clinical Application Specialist, Diopsys, Inc. Faculty: Joanne L. Yawn, COT William E. Sponsel, MD Course Level: Basic
Course Description:
1. Electroretinogram 2. Visual Evoked Potential
“ERG” measures retinal function.
“VEP” measures the function of the entire visual pathway to the visual cortex in the brain.
This lecture is an introduction to commonly used Visual Electrophysiology (EP) tests:
Visual Electrophysiology provides information about visual function that no
other tests provide.
Quantifies - measures the strength and speed of visual signal
Objective test – not based on patient cognitive response
More in-depth, comparative data for physician’s medical decision
Objective: To answer common questions Visual Electrophysiology (EP)
1. WHAT is Visual Electrophysiology (EP)? 2. WHO uses it? 3. WHICH test is used? 4. WHY is it needed? 5. WHEN is it needed? 6. HOW to perform EP?
What is Visual Electrophysiology?
Visual electrophysiology measures the electrical signals in the visual pathway.
1. Electrodes are placed on the head
2. Then they are connected to wires
3. The wires are connected to an amplifier
4. The amplifier is connect to a Computer that analyzes the visual signal.
Basic Technology
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How does visual electrophysiology work?
ERG and VEP use different stimuli to “Evoke” a response
Light 1. Luminance (how bright) 2. Flash or Flicker (speed of
change)
Patterns 1. Different size 2. Different contrast 3. Different Speeds (e.g. pattern reversal)
• Transient (slower) • Steady State (faster stimulus) • On-Off (on off)
Flash Stimulation
Light/Flash Stimulus Example Using mini-ganzfeld, the full Field ERG (ffERG) stimulates primarily Cones
Light Stimuli (Flash or Flicker) Can penetrate mild to moderate opacities to determine
retinal (ERG) and optic nerve function (VEP) function
Ganzfeld
Pattern Stimuli varies for ERG and VEP
1. Patterns/Speed
2. Line size (acuity) with different “Spatial Frequencies”
3. Contrasts
Speed of Stimulus (how fast the stimulus appears or reverses)
Speed of Flash Pattern reversal On-off
https://youtu.be/xEd1h_lz4rA
Spatial Frequencies (how many checks in an area)
16 X 16 64 X 64 32 X 32
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Contrast Variations High Contrast Stimulates Parvo Cells of Retina for Central Vision and Acuity
Low Contrast Stimulates Magno Cells of Retina for early detection of field loss
Example: ERG Pattern stimulates retinal ganglion cells
Pattern Stimulus
pERG measures how well the cells are functioning prior to cell death
as documented by OCT
OCT measures Retinal Nerve Fiber Layer (RNFL) structure after cell death
WHO uses Visual Electrophysiology?
A. Ophthalmologists Adjunctive
Alternative
B. Optometrists Supplemental
Confirm or Differentiate More in-depth analysis Alternative testing/patient limitations
C. Neurologists
Subclinical
Equivocal Location Progression
Core Ophthalmic Knowledge
Accepted for same Clinical Indications as Psychophysical Procedures
AAO Basic Clinical Science Course – Glaucoma 2015-2016
“…pattern electroretinogram, may improve the ophthalmologist’s ability to recognize early glaucomatous visual function loss in patients considered to be glaucoma suspects because of a suspicious optic disc appearance …”
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Accepted in Optometric Clinical Practice Guidelines as Supplemental Testing
https://www.aoa.org/documents/CPG-1.pdf https://www.aoa.org/documents/CPG-14.pdf
Subclinical – “reveal subclinical involvement of a sensory system (“silent” lesions),
particularly when demyelination is suggested by symptoms and/or signs in another area of the central nervous system”
Equivocal – “demonstrate abnormal sensory system conduction, when the history
and/or neurological examination is equivocal”
Location – “help define the anatomic distribution and give some insight into
pathophysiology of a disease process”
Progression – “monitor changes in a patient’s neurological status.”
P Walsh, N Kane, S Butler. The clinical role of evoked potentials. J Neurol Neurosurg Psychiatry 2005;76:ii16-ii22 doi:10.1136/jnnp.2005.068130
Required in Vision Care for the same reasons it’s used in Neurology
Glaucoma
Maculopathies Inherited retinopathies
Drug toxicities
To Differentiate ophthalmic from
other causes:
Neurological Infectious Vascular
Endocrine Neoplastic
Autoimmune Trauma
Toxic
WHICH test is needed?
VEP
ERG
Clarify, locate, quantify, monitor retinal function:
OR For vision
disorders that affect the optic
nerve or pathway (amblyopia)
International Society of Clinical Electrophysiology of Vision VISUAL ELECTRODIAGNOSTICS: A Guide To Procedures
Defines clinical use of Electrophysiology
Standards, Recommendations and Guidelines (ISCEV)
Confirmation of Neurological or Ophthalmological Disease Unexplained Visual Loss Pediatric Neurology Opacities in Media Monitoring Health - Toxicity Detection of the Disease or Carrier States of Inherited Visual Disorders Quantitative Assessment of Visual Disease Assessment of Retinal and Optic Nerve Function Following Trauma Infants with questionable vision
http://www.iscev.org/standards/proceduresguide.html
International Society of Electrophysiology for Vision (ISCEV) Standards, Recommendations and Guidelines VISUAL ELECTRODIAGNOSTICS
Test Selection simplified for Physician’s Order
ERG with Light/Flash
International Society of Electrophysiology for Vision (ISCEV) Standards, Recommendations and Guidelines VISUAL ELECTRODIAGNOSTICS
Test Selection simplified for Physician’s Order
ERG with Pattern
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International Society of Electrophysiology for Vision (ISCEV) Standards, Recommendations and Guidelines VISUAL ELECTRODIAGNOSTICS
Test Selection simplified for Physician’s Order
Flash VEP or Flash ERG
International Society of Electrophysiology for Vision (ISCEV) Standards, Recommendations and Guidelines VISUAL ELECTRODIAGNOSTICS
Test Selection simplified for Physician’s Order
VEP Pattern
International Society of Electrophysiology for Vision (ISCEV) Standards, Recommendations and Guidelines VISUAL ELECTRODIAGNOSTICS
Test Selection simplified for Physician’s Order
Special VEP
WHY is EP needed?
Structural Tests (SCODI)
Functional Tests (Psychophysical Acuity, Field, Contrast)
Irreversible loss
VS.
Functional changes can precede structural loss and field loss
Function is an Important Component for Medical Decisions
Objective more reliable than subjective
Already Damaged
Earlier Intervention to prevent visual loss
When does the doctor require measures of function?
Source: AAO Preferred Practice Patterns
Three Categories of Patients seen in Ophthalmic Practice 1. No Risk 2. At Risk 3. Established disorder
a. Other conditions that require intervention
All patients require some measure of function
Category I - Table 1: No Risk Factors
Category II - Table 2: Patients with Risk Factors
Diabetes 1,2, Pregnant, Glaucoma
Category III - Table 3: Conditions that require Intervention/Asymptomatic Ocular Disease
Glaucoma
Diabetic Retinopathy
AMD
Cataract w/ or w/o Ocular
Category III(Other): Conditions that
Require Intervention
Ophthalmic abnormalities
Vision Rehab
Amblyopia (Pediatrics)
Acuity Field
Pin hole
no
Source: AAO Preferred Practice Patterns
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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
EP Alternative Testing Circumstances
Alternative Function Test (to acuity, field or contrast)
Other Functional Test Limitations:
High false positive (other) test result Unreliable (other) test result
Patient Limitations: (special needs)
Unable to cooperate or understand other procedures Physical limitations Cognitive limitations Preverbal (pediatrics)
Excessive High False Positives Low Test Reliability
It’s important to get reliable measures of function for diagnosis and treatment
Alternative Function Test Alternative Function Test
https://www.google.com/search?q=images+difficult+eye+exam&espv=2&biw=1280&bih=919&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwikzom7u6_LAhUmtYMKHZH_A2sQsAQITQ#imgrc=DoUo6BLPtRmAuM%3A
Cognitive, language and special needs
(Subclinical, asymptomatic conditions that are below the surface of clinical detection )
Adjunctive (for more in-depth assessment)
Equivocal Diagnoses:
• Confirm or rule out differential diagnoses • Patient complaints inconsistent with other test results • Other test results questionable or borderline • Multiple risks factors for subclinical/asymptomatic disorder
Location:
• VEP for optic nerve or retrobulbar dysfunction • ERG to isolate dysfunction, ERG used after abnormal VEP
Progression:
• To quantify level of severity or progression • To track for changes in condition or treatment efficacy
EP Adjunctive Testing Circumstances Equivocal Diagnosis
Retinal Concern
Retrobulbar concern (optic nerve to visual cortex)
Patient w/ Cataract and Retinal Concern
Flash VEP
Flash Flicker ERG
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Locate the area of dysfunction for treatment or referral
pERG is performed Abnormal VEP prompts an pERG
Abnormal VEP pERG is normal
Dysfunction is retrobulbar
pERG is performed Abnormal VEP prompts an pERG
Abnormal VEP pERG is Abnormal
Isolated dysfunction to the retina
Isolate the dysfunction in the Retina with pERG
pERG is performed
pERG is Abnormal
pERG shows Retinal function is changing
Retina concern only (e.g. glaucoma suspect)
Objective measure of function Earlier detection Monitor progression Treatment Efficacy
Technician alerts physician when patient is unable to produce reliable results on psychophysical tests • pERG for glaucoma suspects • Flicker ffERG for maculopathies • pVEP for amblyopia
Physician Clinical Testing Protocols
Physician considers EP for subclinical concerns • Questionable/borderline standard test findings • Multiple risk factors • Locate dysfunction for treatment or referral • Monitor for functional changes for treatment efficacy or plan change
(Refer to ISCEV Standards and Clinical Evidence for test selection)
a. Based on Medical Necessity (to improve structure or function)
b. Only known Contraindication – if history of seizures (Doctor’s decision if test result is more valuable to patient care than risk)
d. Physician documents test reason in chart/EMR and orders test
• Specify test and stimulus
When does the Physician order?
c. When ordering ERGs with intraocular ERG electrode placements, consider patient tolerance.
HOW are the tests performed? 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
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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
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
http://webvision.med.utah.edu/book/electrophysiology/the-electroretinogram-clinical-applications/
Performing the ERG test
• Electrodes are connected by wire to an amplifier and computer
• Test is run
• Computer analyzes patient response
• Report to doctor
• Similar to VEP
Reference Ground Active
VEP Electrode Placement Made Simple
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
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Different Electrophysiology Tests Produce Different Results
• The signal from the patient is generally measured in strength (microvolts) and speed (milliseconds).
• These measures product test results (wave forms).
• Wave forms will look different due to the area tested (retina or pathway) and the type of stimuli used (flash vs. pattern).
• Familiarize yourself with the Manufacturer Operation Manual for the desired, quality wave form.
Summary:
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.
Questions?
THANK YOU!
aanderson@diopsys.com