Notes on the Electroretinogram ERG response
• a-wave arises primarily from the photoreceptors.
• b-wave arises primarily from the bipolar and Müller cells.
• OPs ( Ocillatory Potentials) arise primarily from amacrine cells.
Different ERG Electroretinogram responses in common diseases :
1- reduced a- and b-waves
• Rod–cone dystrophies (including RP)
• Total retinal detachment
• Metallosis
• Drug toxicity (e.g. phenothiazines)
• Autoimmune retinopathy
• Cancer-associated retinopathy (CAR)
• Ophthalmic artery occlusion
2- normal a-wave, reduced scotopic b-wave
• CSNB
• X-linked retinoschisis (XlRS)
• CRAO or CRVO
• Myotonic dystrophy
• Oguchi’s disease
• Quinine toxicity
• Melanoma Associated Retinopathy (MAR)
3- Abnormal phototopic and normal scotopic ERGs
Achromatopsia
Cone dystrophy
4- Reduced OPs
• Diabetic patients, can correlate with an increased risk of developing severe proliferative diabetic
retinopathy (PDR)
• Drug toxicity
Notes on the Electroretinogram ERG response videos
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Notes on the Electroretinogram ERG response PowerPoint presentation :
ERG Electroretinogram
1. Dr,.Arvind Jain M ELECTRO-RETINOGRAPHY DR.ARVIND
2. ELECTRORETINOGRAM • Holmgren in 1865 first demonstrated that an alteration in electrical potential occurred when light fell on retina. • In 1877. Dewar recorded light evoked electrical response, ERG, from humans for the first time. • In 1941, Riggs introduced the contact lens electrode in humans DR.ARVIND
3. INTRODUCTION • Electrodes placed on cornea • Retina stimulated • Resultant wave recorded and analyzed • Helps study eye, systemic diseases DR.ARVIND
4. ELECTRORETINOGRAPHY • ERG is a recording of changes in resting potential in the retina when stimulated with a brief flash of light. DR.ARVIND
5. ERG CONSIST OF • Electrodes for recording of the resting Potential • Light stimulating device to deliver standardized flash of light • Differential amplifier Glaucoma High pressure Aqueous humor DR.ARVIND
6. ELECTRODES • Three electrodes required 1. Active electrode Corneal -Burian Allen (Bipolar) -Jet electrode (Unipolar) Non corneal electrode -DTL fiber electrode (Dawson-Trick-Litzkow) -Gold foil electrode -LVP Zari electrode 2. Ground electrode- on patients earlobe 3. Reference or inactive electrode -on patient forehead DR.ARVIND
7. BURIAN-ALLEN ELECTRODE FOR HUMAN USE DR.ARVIND
8. ELECTRODE IMPEDED IN A SPECIAL CONTACT LENS. DR.ARVIND
9. LIGHT STIMULATION FOR ERG • Several methods of stimulating the eye. • Some laboratories use a strobe lamp that is mobile and can be easily placed in front of a person whether sitting or reclining. DR.ARVIND
10. GANZFELD • ERG is recorded using Ganzfeld which is integrating sphere used to deliver stimuli • Patients over 5 years of age • Provides graded intensity of flash stimulation, diffuse background & fixation lights DR.ARVIND
11. • The Grass xenon- arc photo stimulator can also be used for delivering stimuli. GRASS XENON-ARC PHOTO STIMULATOR DR.ARVIND
12. PROCEDURE There are many ways of recording ERGs from patients. Some laboratories record the light adapted state first and others dark-adapt first. Dark adapt the Eye for 30-45min Anesthetize subjects cornea (paracaine) Dilate iris (tropicamide; phenylephrine) DR.ARVIND
13. RECORDING OF ERG Attach electrodes: • Forehead (negative-Reference electrode) • Corneal (positive-Burian Allen) • -using non viscous coupler (CMC) • Behind Ear (Ground electrode) Patient is made to sit in front of Ganzfeld Stimualtor DR.ARVIND
14. The light stimulus consist of flashes of light of about 5 ms so that each flash is considerably shorter than integration time of any photo receptor A Standard Flash (SF) strength is defined as one that produces a stimulus strength of 1.5 – 4.5 candela second per meter square[cd.s/m²] STIMULUS OF LIGHT DR.ARVIND
Electrophysiology (ERG and EOG) Simplified
ELECTRORETINOGRAPHY (ERG) & ELECTROOCULOGRAPHY (EOG) Dr Sumeet Agrawal Vitreo-Retina Fellow Narayana Nethralaya Bangalore
Notes on the Electroretinogram ERG response
