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

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

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

Methods n Dark adapt 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)

ERG set-up for anesthetized rat.

Burian-Allen Electrode for Human Use

Burian-Allen Electrode for MOUSE

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

Electroretinogram (ERG) B wave A wave

Oscillatory Potentials (OPs)

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

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.

Different conditions yield different responses Rod Rod & Cone Cone

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

Granit’s Landmark Study

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

Isolated retina preparation (No RPE)

Electroretinogram (ERG) A wave

Oscillatory Potentials (OPs)

OP are stable measures

r (µV) time (s) Week 1 Week 2 Week 9 Oscillatory Potentials are delayed in diabetes

Normal RP-> Cone-Rod Dystrophy -->

The multifocal ERG (mERG)

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

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

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

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

Faster flicker smaller response

Define CFF critical flicker frequency

ERG derived CFF

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?

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

Rods die first, then cone function fails

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

Human Flicker: maximum flicker sensitivity CFF = threshold detection

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

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

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

Human Flicker: Timing & Amplitude are important