ASCRS ♦ ASOA Symposium & Congress

Technicians & Nurses Program

May 6-10, 2016 – New Orleans

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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