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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