Download Electrophysiology in Paediatrics What is Electrophysiology ? Visual

Electrophysiology in Paediatrics
What is Electrophysiology ?
What is it and Why is it used?
• Electrophysiology describes a range of
tests designed to record electrical activity
in response to ocular stimulation
• Investigate the function of the retina and
visual pathway
• Diagnostic tool
• Non-invasive and objective assessment
Stephanie Sendelbeck & Louise Brennan
Visual Electrodiagnosis
• Electroretinogram
• Visual Evoked
Potential
• Electrooculogram
Electroretinogram (ERG)
• Investigates rod and cone function, as
well as inner and outer retinal function
• Three methods:
– Full Field (ffERG)
– Pattern (PERG)
– Multifocal (mfERG)
Full Field ERG
• Most common method used in the Eye
Clinic
• Mass electrical response of widespread
retina to light stimulation
• Involves light stimulation of the retina via
the Ganzfeld bowl or Kubersfield hand held
light source
• Patient does not need to fixate on the light
source and can be asleep throughout
testing
Full Field ERG
• Suitable for diagnosing retinal
dystrophies such as
– Retinintis Pigmentosa
– Congenital Stationary Night
Blindness
– Cone Dystrophy
Equipment
•Abrasive Gel Skin Cleaner
•Alcohol Wipes
•Electrode Gel
•Electrode Cream
•Micropore Tape
•Eye Patch
Electrodes
SKIN
Useful on younger /
non-compliant
patients, results will
require amplification
(12% of CL
electrode response)
ERG JET
GOLD FOIL
More comfortable than
contact lens electrode
and less amplification
required compared to
skin (47%)
BURIAN-ALLEN
Contact lens electrode with built in lid
speculum. Has both negative and positive
reference built in. Requires lots of cooperation from patient and is difficult to fit
in children’s eyes. Provides the best results.
Contact lens electrode. Requires patient cooperation and difficult to use in children
without sedation. Result requires no
amplification.
This is our electrode of choice and is used in
older co-operative patients or patients under
general anaesthetic
Protocol
• Pupils dilated
• Patient, parent and orthoptist sit in dark
room for 20 minutes to adapt eyes to dark
to allow rod function. A dim red light only
is allowed
• Skin on the face is cleaned with
exfoliating gel and alcohol wipe
• Electrodes are attached. If ERG-Jet or
Gold Foil electrodes are used a topical
anaesthetic is instilled prior to insertion
Protocol
ISCEV Standards
• Patient is seated either at Ganzfeld bowl
(older patients) or comfortably in parents
arms (younger patients)
• Recording following ISCEV standards
begin
• Patient, parent and orthoptist sit in light
room for 10 minutes to adapt eyes to the
light
• Recording following ISCEV standards
continues
Electrode Placement
International Society for Clinical
Electrophysiology of vision
• Scotopic (rod response) dim flash -24dB
• Scotopic (mixed cone and rod response)
bright flash 0dB
• Photopic (cone response) bright flash
0dB
• Photopic Flicker bright flash 30HZ
Electrode Placement
Skin
Skin Electrode
placed
underneath the
eye (recording /
positive) and on
lateral canthus
(reference /
negative)
ERG-Jet / Gold
Foil placed on the
eye (recording /
positive) and skin
electrodes on
lateral canthus
(reference /
negative)
Ear Clip
Electrode
placed on
ear
(ground)
Contact Lens/Gold Foil
Results
Waveforms are analysed by:
• ‘a’ wave – initial negative trough
originating from photoreceptor layer
• ‘b’ wave – positive peak after a wave
originating from Muller cells and bipolar
cells
• Amplitude – measured from trough to
peak
• Implicit time – where the wave occurs
along the time base
The Retina
b wave
a Wave
b Wave
a wave
When is a GA necessary?
• Poor co-operation
• Developmental Delay
• Patient who is already having EUA or
other procedure under GA and has
been referred for ERG
• Only ffERG can be performed under
GA with handheld light source
• Pattern, Multifocal and VEP techniques
can not be performed under GA as
fixation is required
Pattern ERG
• Elicited to pattern stimulation, usually
checkerboard or gratings
• Much lower amplitude than flash ERG
• Fixation crucial
• Reflects activity in the ganglion cell
layer
• Helps to isolate macular function
Multifocal ERG
• Latest technology in ERG assessment
• Localised cone responses from the
central 20-30 degrees of the retina to
pattern stimulation
• Powerful clinical tool for detecting
local retinal abnormalities
• Multifocal ERG has just been obtained
by the clinic and further training is
being undertaken
Results
•Analysed by two
markers
•N35 – small initial
negative trough
occurring at 35ms
•P50 – positive peak
occurring at 45-60ms
Multifocal ERG
• Suitable patients include:
– Stargardt’s disease
– Plaquenil retinopathy
– Diabetic retinopathy
– Unexplained visual loss
– Macular dystrophy / Cone dystrophy
– Branch vein occlusion and central
retinal vein occlusion
Results
Visual Evoked Potential (VEP)
• Investigates visual pathway from retina to
cortex
VEP
• Useful in diagnosis of:
– Cortical Vision Impairment
– Delayed Visual Maturation
– Decreased Visual Acuity not
responding to treatment ie glasses or
occlusion
– Malingering / Functional Patient
– Early Onset Nystagmus
– Optic Nerve / Pathway lesions
• Pattern Reversal
– Full field stimulation most widely used
clinically as allows least variation in
waveform and timing
– Uses reversing checkerboard pattern
– Fixation is crucial
FIVE METHODS
• Flash VEP
– Useful in unco-operative patients, those
with nystagmus or functional loss
– Uses flashing light as stimulation
– 80 flashes of light are averaged for result
• Pattern Onset
– Useful to detect malingering and in
patients with nystagmus
– Uses checkerboard pattern which
flashes on and off
– Not as reliant on fixation as pattern
reversal
Electrodes
• Sweep
– Enables VA to be measured
– Uses sweeping gratings of varying sizes
• Multifocal
– Assesses if stimulation to specific visual
field locations elicit cortical activity
Most commonly used in the Eye Clinic
are the PATTERN REVERSAL and FLASH
methods
Electrode Placement
Gold Cap
Electrode
placed 2.5cm
above Inion
with electrode
cream
(recording /
positive)
Skin Electrode
placed on
forehead with
electrode gel
(reference /
negative)
Ear Clip
Electrode
placed on
earlobe with
electrode
gel (ground)
Protocol – FLASH VEP
• No dilation required
• Skin is cleaned with abrasive gel and
alcohol wipe
• Electrodes are attached
• One eye occluded
• Patient is seated at Ganzfeld bowl
(older) or comfortably in parents arms
(younger)
• Patient watches a flashing light
• 80 Flashes averaged
Protocol – PATTERN VEP
• No dilation required
• Glasses worn for testing
• Skin is cleaned with abrasive gel and
alcohol wipe
• Electrodes are attached
• One eye occluded
• Patient is seated at 1m from pattern monitor
• Patient watches a checkerboard pattern of
reversing checks
• Different check sizes assessed from large to
small
Results
Waveforms are analysed by:
• Latency – where the wave occurs
along the time base
• Amplitude – measured from trough to
peak
Pattern VER
Pattern Reversal
Oz
30
25
20
15
• P100 – positive peak at 100ms
10
1: (uV) OzR
• N75 – initial negative trough at 75ms
5
0
-5
-10
• N135 – negative trough at 135ms
-15
-20
8x8 100% Contrast Checks 2 Hz
-25
-30
0
50
100
150
milliseconds
200
250
Kurbisfeld VEP
Flash
Oz
50
25
1: (uV) OzR
• Occurs later on time base and is a
much slower response than pattern
reversal VEP
0
-25
-50
Scotopic 0 dB , White 2 Hz
0
What’
What’s involved in an
Electrophysiology Appointment?
• Referral from ophthalmologist
• Visual Acuity
• Colour vision
• Visual field
• ERG and / or VEP
• Fundus Photos
An Electrophysiology appointment can
take up to 2 hours
50
100
150
milliseconds
200
250
The Orthoptists Role….
Like in a lot of clinical areas that
orthoptist specialise in the 3 P’s are
necessary
Practice
Perseverance
Patience +++
Summary
• Electrophysiology is an important
diagnostic tool in paediatrics
• It is useful for diagnosing a range of
conditions including:
– Retinal Dystrophies
– Cortical Vision Impairment
– Functional Loss / Malingering
– Congenital Nystagmus
THANK YOU
•Results are always to be used in
conjunction with other tests and findings
•Useful in genetic conditions / counselling