1. All You Ever Wanted to Know About ERG but Were Afraid to Ask
American Academy of Ophthalmology, Orlando, 2002
10 November 2018

2. Testing Levels of the Visual System
clinical neurophysiology allows assessment of retina, optic nerve, chiasm, and retrochiasmal visual pathways
the ERG can functionally dissect the neural retina
10 November 2018

3. Electroretinogram (ERG)
ERGs are mass electrical activity from the retina in response to visual stimulation
the ERG is objective, non-invasive measure of electroretinal function OD OS a b
100 Uv
25 ms
10 November 2018

4. Recording the ERG
Photic
stimulator
Plotter
electrode

5. Microconductive Thread
ERG Electrodes
Contact Lens
Electrode
Microconductive Thread
Electrode
10 November 2018

6. Modern ERG Recording Electrodes
DTL-Plus™ Microconductive Thread Electrode
10 November 2018

7. ERG Electrodes Microconductive thread electrode neglible mass
convenient to use, disposable
no interference with pupil or optics
reliable ERG recordings
well tolerated by children
Microconductive
thread electrode
10 November 2018

8. Pre-Millenium ERG Technology
Ganzfeld Stimulation (full-field)
provided by xenon flash photostimulator
full visual field stimulation
stimulus intensity
stimulus wavelength
variable stimulus rate
variable background intensity
10 November 2018

9. Modern ERG Stimulator
10 November 2018

10. Mini-Ganzfeld LED Stimulator
4.5 inch diameter
176 LEDs
“blue” (470 nm)
“green” (525 nm)
“red” (640 nm)
7 log unit luminance range
optoelectronic stimulation can be more precisely controlled and calibrated than xenon discharge tubes
Espion Colorburst™
10 November 2018

11. Components of the Flash ERG
11/10/2018
Components of the Flash ERG
b-wave
Implicit time (i.t.)= time from stimulus
until peak of activity
b i.t.
Amplitude (amp)= voltage magnitude
at peak of activity
b amp
a amp
a i.t.
a-wave

12. Generator Sites of the Flash ERG
a-wave originates from the photoreceptor layer
b-wave is a glial potential originating from the Müller cell and the bipolar cells
OPs originate from amacrine cells
flash ERG reflects electroretinal activity distal to the ganglion cell layer
10 November 2018

13. Oscillatory Potentials (OP)OD OS
5 Uv
15 ms
a subcomponent of the ERG seen on ascending limb of the b-wave
Wachtmeister (1977) demonstrated OPs originate from amacrine cells in the inner plexiform layer
10 November 2018

14. Rod vs Cone ERGs Rod ERG OPs Cone ERG 30 Hz Flicker 10 November 2018

15. Pattern ERG (PERG)
Elicited to pattern stimulation (usually checkerboard or bar gratings)
much lower amplitude than flash ERGs
fixation is critical for PERG, not flash ERG
PERG reflects activity in the ganglion cell layer
10 November 2018

16. Generators of the Pattern ERG
PERGs are generated in the ganglion cell layer
PERGs may reflect both activation of cell body and axonal activity
10 November 2018

17. ISCEV ERG Standards
International Society for Clinical Electrophysiology of Vision (ISCEV)
ERG standard established in 1989
standards for 5 commonly obtained responses
ERG developed by the rods (dark-adapted)
maximal ERG response (dark-adapted)
Oscillatory Potentials
ERG developed by the cones (light-adapted)
ERG to flicker
10 November 2018

18. Who are the Clients of an Electrodiagnostic Service?
Patients whose eyes have:
symptoms suggestive of known neurological or ophthalmological disease
unexplained visual loss
medico-legal problems
workman’s compensation
defects associated with psychiatric disturbance, mental or physical handicap
pediatric neuro-ophthalmic practice
metabolic, hereditary or neurological disease with visual impairment
non-seeing child
10 November 2018

19. Who are the Clients of an Electrodiagnostic Service?
Patients with media opacities
prior to corneal grafting or cataract surgery
vitreous hemorrhage (in DR or following trauma, RD)
Patients with uveitis or inflammatory eye disease
Patients with suspected disease or carrier status of inherited visual disorders
Patients requiring quantitative assessment of disease progression
Assessment of retinal and optic nerve function following trauma
10 November 2018

20. Indications for ERG
aid to diagnosis in patients suspected of having stationary or progressive inherited retinal degenerations
to rule out clinically unaffected family members
to evaluate possible female carriers of x-linked disease
to assess patients with retinal toxicity due to metallosis (siderosis)
retinotoxic or neurotoxic medications
chloroquine, Hydroxychloroquine, ethambutol, phenothiazine
Desferrioxamine, Tamoxifen
Vigabatrin toxicity?
patients with OHT/glaucoma
to identify eyes that are likely to develop neovascularization in diseases such as CRVO and DR
documenting therapeutic effects of surgery or medication
10 November 2018

23. Electrodiagnostics of the Future
Standardized instrumentation
Standardized testing protocols
Multicenter normative data collection
Web-based telemedicine application
University of Ottawa Eye Institute announces ERG Reading Centre
10 November 2018