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

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

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

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

6. ERG set-up for anesthetized rat.

7. Burian-Allen Electrode for Human Use

8. Burian-Allen Electrode for MOUSE

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

10. Electroretinogram (ERG) B wave A wave

11. Oscillatory Potentials (OPs)

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

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

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

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

16. Granit’s Landmark Study

17. RPE & Müller cells combine to create the c-wave Due to K+ pumping

18. Isolated retina preparation (No RPE)

19. Electroretinogram (ERG) A wave

20. Oscillatory Potentials (OPs)

21. OP are stable measures

22. 100 50 0 -50 r (µV) 0.100.050.00 time (s) Week 1 Week 2 Week 9 Oscillatory Potentials are delayed in diabetes

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

24. The multifocal ERG (mERG)

26. Gentamycin kills the retina: Brief exposures are reversible. Dose dependent loss of b-wave. Toxicity studies of “new” agents

27. 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

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

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

30. Faster flicker smaller response

31. Define CFF critical flicker frequency

32. ERG derived CFF

33. 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?

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

35. Rods die first, then cone function fails

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

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

38. Younger ( 50) Human Flicker ERG by K. Bowles UAB Class of 2009.

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

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

41. Human Flicker: Timing & Amplitude are important