Electrophysiology in Paediatrics What is it and Why is it used? What is Electrophysiology? Electroretinogram (ERG) Visual Electrodiagnosis

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Margaret Wood
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1 Electrophysiology in Paediatrics What is it and Why is it used? What is Electrophysiology? 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

2 Equipment Abrasive Gel Skin Cleaner Alcohol Wipes Electrode Gel Electrode Cream Micropore Tape Eye Patch SKIN Electrodes 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%) 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 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. 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

3 Protocol 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 ISCEV Standards 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 Electrode Placement Skin Contact Lens/Gold Foil 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)

4 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

5 The Retina b wave a Wave b Wave a wave

6 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 Results Analysed by two markers N35 small initial negative trough occurring at 35ms P50 positive peak occurring at 45-60ms Multifocal ERG Latest technology in ERG assessment Localised cone responses from the central 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 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

7 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 Flash VEP FIVE METHODS 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 Reversal Full field stimulation most widely used clinically as allows least variation in waveform and timing Uses reversing checkerboard pattern Fixation is crucial 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

8 Sweep Enables VA to be measured Uses sweeping gratings of varying sizes Electrodes 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 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) Electrode Placement 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

9 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 P100 positive peak at 100ms 10 1: (uv) OzR N75 initial negative trough at 75ms N135 negative trough at 135ms x8 100% Contrast Checks 2 Hz milliseconds

10 Flash 50 Oz Kurbisfeld VEP Occurs later on time base and is a much slower response than pattern reversal VEP 1: (uv) OzR Scotopic 0 db, White 2 Hz milliseconds 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

11 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

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