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Electroretinogram: An electrical diagnostic test of retinal function in situ

Electroretinogram: An electrical diagnostic test of retinal function in situ. Electro -part Currents, wires, voltage, resistance Retino - part Cell types, membrane potential, radial currents. Gramo - part Diagnostic test of patient retinal health

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Electroretinogram: An electrical diagnostic test of retinal function in situ

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  1. Electroretinogram: An electrical diagnostic test of retinal function in situ • Electro -part • Currents, wires, voltage, resistance • Retino - part • Cell types, membrane potential, radial currents. • Gramo - part • Diagnostic test of patient retinal health • Research test retinal circuitry, cell function, disease states, drug efficacy

  2. Goals • Introduce the ERG, its components, and where they originate. • Show you the basic clinical test • Show some research examples

  3. The Eye generates a lot of electrical signal, some fast . . some slow. . .

  4. Methods • Dark adapt 20-45 min • Anesthetize subjects cornea (paracaine) • Dilate iris (tropicamide; phenylephrine) • Attach electrodes: Burian-Alled, Or • Forehead (neg) • Corneal (pos) (DTL microfiber) • Behind Ear (reference)

  5. ERG set-up for anesthetized rat.

  6. Burian-Allen Electrode for Human Use

  7. Burian-Allen Electrode for MOUSE

  8. Family of flash responses from threshold to 600,000 fold brighter stimuli

  9. B wave A wave Electroretinogram (ERG)

  10. Oscillatory Potentials (OPs)

  11. Basic components of ERG • a-wave : derived from photoreceptors • Latency & Amplitude (dark adapted and light adapted) • b-wave : derived from ON bipolar cells • Latency & Amplitude (dark adapted and light adapted) • OPs : oscillatory potentials, derived from the inner retina: amacrine and G-cells

  12. Basic Clinical ERG tests • Dark adapted, dim (blue) flash response • Isolated rod-driven response • Dark adapted, bright (white) flash response • Generates Max a-wave, b-wave, also generates OPs : • Light adapted, bright flash • Isolated cone-driven response • 30 Hz Flicker • Another method of isolating cone responses.

  13. Different conditions yield different responses Rod Rod & Cone Cone

  14. Dual retina: Great amounts of time and energy have been devoted to separating rod- and cone-driven responses

  15. Granit’s Landmark Study

  16. RPE & Müller cells combine to create the c-waveDue to K+ pumping

  17. Isolated retina preparation (No RPE)

  18. A wave Electroretinogram (ERG)

  19. Oscillatory Potentials (OPs)

  20. OP are stable measures

  21. 100 Week 1 Week 2 Week 9 50 r (µV) 0 -50 0.00 0.05 0.10 time (s) Oscillatory Potentials are delayed in diabetes

  22. Normal RP-> Cone-Rod Dystrophy -->

  23. The multifocal ERG (mERG)

  24. Flicker ERGs Using the difference in the speed of the rod (slow) and cone (fast) responses to isolate rod- and cone-driven function in the retina

  25. Measuring CFF at 1 intensity • Measure Flicker response ERG • Average a single wave • Measure amplitues • Plot amplitude of response vs. Frequency of flicker. • Make a linear regression line to data • CHOOSE A CRITERION RESPONSE AMPLITUDE TO DEFINE CFF

  26. ERG to 5 sec of Flicker Three separate stimuli, each with a different frequency.

  27. Faster flicker smaller response

  28. Define CFFcritical flicker frequency

  29. ERG derived CFF

  30. Studies of CFF at various background intensities can isolate and quantify rod- and cone-driven visual response. The next slides show the CFF curves of two rodent models of eye diseases, can you tell which effects preferentially the rod system? And which effects both rod and cone systems?

  31. PN44 RCS rat vs. wild type rat • Open symbol represent results from wild-type rats. • Filled circles represent results from RCS dystrophic rats • PN23 = post-natal day 23 PN23 Rubin & Kraft, Documenta Ophth. 2007

  32. Rods die first, then cone function fails

  33. Mouse Rod Channel Mutant Rod Function: very poor Cone Function: Preserved PN 32 PN 75 PN 90

  34. Human Flicker:maximum flicker sensitivity CFF = threshold detection

  35. Younger (< 30 ) vs Older (>50) Human Flicker ERG by K. Bowles UAB Class of 2009.

  36. ERP ms timescale: photoreceptor signal Early Receptor Potential Normal carriers affected 50 µv 0.5 ms X-linked RP Berson & Goldstein IOVS 1970

  37. LP timescale minutes : source RPE The Light Peak: a depolarization of the RPE cells 7 minutes A calcium dependent depolarization of the RPE cells generates the LP which can be seen as an oscillation on top of the EOG Marmostein et al. J. Gen. Physiol. 2006

  38. Human Flicker:Timing & Amplitude are important

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