1. Clinical electrophysiology:
Plugging into the visual system
Marlee M. Spafford, OD, MSc, PhD, FAAO

2. COPE Personal Disclosure
For this lecture, I have:
developed the course material independently
developed the course material without commercial interests
no personal conflicts of interest
no financial relationship with a commercial interest

3. Basic Electrodiagnostic Equipment
Specialized computer hardware & software
>$100,000 Cn
Pattern stimulator
Ganzfeld (flash stimuli)

4. Visual Electrodiagnostic Tests
Electroretinogram (ERG)
Electro-oculogram (EOG)
Visually Evoked Potential (VEP)

5. Electroretinogram (ERG)
Reflects global changes in retinal electrical potential in response to flash or pattern stimuli

6. Electro-oculogram (EOG)
Records the ocular standing electrical potential
Dark-adapted with light-adapted
Reflects gross outer retina/RPE function + -

7. Visually Evoked Potential (VEP)
Assess macular-cortical pathway’s gross integrity
Record

8. Patient #1: 6-yr-old male
VEP referral (family OD):
Reduced VA, not corrected by spectacles: meridional amblyopia?
OD: -1.00/-3.00 x /12
OS: -2.00/-3.50 x /15
Interview:
Ocular Hx:
1st 4 yrs
Nyctalopia: “always trips in the dark”
Health Hx:
Unremarkable
Birth Hx:
Polydactyl 1 yr)
Negative family hx of eye disease
1 step-brother (“normal” vision)
No parental consanguinity

9. Nyctalopia Causes: Problem Specific Testing: Retinitis pigmentosa (RP)
Choroideremia
Congenital stationary night blindness (CSNB)
Pan-retinal laser surgery
Vitamin A deficiency
Non-retinal
Night myopia
Optical defects (e.g., cataract)
Problem Specific Testing:
DFE
Visual fields
Automated > 30o; Goldmann
ERG (full field ERG)
Colour Vision
adults; B-Y & R-G defects

10. DFE

11. Bardet-Biedl Syndrome
AR inheritance
1/179 carry gene
Progressive vision loss
Nyctalopia
Constricted Fields
Acuity loss
Optometrist duties:
Low vision care
Referral for genetic work-up
Referral to nephrologist
Cardinal Features (4 of 6)
Retinal dystrophy (RP)
Polydactyly
Obesity
Cognitive impairment
Hypogonadism
Nephropathy

12. Retinal-based Function Tests
ERG
Full-field ERG: fERG (typical referral)
Pattern ERG: pERG
Multi-focal ERG: mfERG
EOG

13. Full-field ERGs
Assess the gross integrity of the outer 2/3rds of the neural retina
Good test for:
widespread retinal diseases
vision loss that changes with lighting conditions
fERG

14. fERGs Standardized fERG protocol exists:
ISCEV standard: (International Society for Clinical Electrophysiology of Vision)
Dark adapt (>20 min): scotopic ERGs (rod-isolated & rod-cone mixed)
Light adapt (>3 min): photopic ERGs (cone-isolated)

15. Measuring fERGs a-wave: Amplitude & implicit time
b-wave: Amplitude & implicit time

16. fERG Components a-wave: Photoreceptors b-wave: Müllers & On-Bipolars
Oscillatory potentials (OPs): Amacrines

17. ISCEV Recording Electrodes
Gold Standard
Contact lens electrode (e.g., Burian-Allen Speculum Contact Lens Electrode)
Bipolar electrode design
CL: active
Speculum: reference

18. ISCEV Recording Electrodes
Other ISCEV Electrodes
DTL Fiber
Gold foil
HK loop

19. DTL Fiber Electrode Insertion

20. Ganzfeld View

21. Chin Rest Prep

22. ERG Recording

23. ERG Recording

24. Simulated fERG Normative Database (Amplitude [µV]: 20-39 yrs)
Supernormal = > 100th percentile
WNL = ≥ 5th percentile
Diminished = < 5th percentile

25. Diagnostic Uses of fERG
Inherited retinal disorders
RPE photoreceptor disease, photoreceptor disease, chorioretinal dystrophies, vitreoretinal dystrophies
Retinal ischemic disease
diabetic retinopathy, central retinal vein occlusion, carotid artery stenosis, sickle cell retinopathy
Pre-surgical evaluation
obstructed retina due to cataract, hemorrhage or penetrating injury
Retinal toxicity
hydroxychloroquine
Unexplained vision loss

26. fERG: RPE-Photoreceptor Disease
rod
maximal
flicker
cone

27. fERG: Photoreceptor Disease
rod
maximal
flicker
cone

28. fERG: Photoreceptor Disease
rod
maximal
flicker
cone

29. pERG (seldom done)
Reflects central retinal response (incl. ganglion cell)
Macular disease
Toxic/nutritional disease
Unexplained central vision loss
2012 ISCEV standard

30. mfERG
2011 ISCEV standard
Topographical measure of outer 2/3rds of retina
~ small retinal areas
Local ERGs are mathematical extractions of the signal
Dilated pupils; fiber electrode

31. Diagnostic Uses of mfERG
Macular disease
e.g., Stargardt Disease, ARMD
Unexplained central vision loss

32. mfERG
ARMD mfERG
Normal mfERG

33. Electro-oculogram (EOG)
Seldom done
2010 ISCEV standard
Reflects global outer retina/RPE function
Clinical diagnostic use:
Best vitelliform macular dystrophy (rare, AD inheritance)
EOG

34. EOG + - Eyes have a ‘standing potential’ Cornea positive; RPE negative
Derived from RPE; changes with retinal illumination
Potential decreases in dark; increases in light
Test involves:
Making lateral saccades through a dark & light phases + -

35. EOG Arden Ratio Light peak (LP)/dark trough (DT) >2.0: normal
1.5 to 2.0: borderline
<1.5: abnormal

36. Patient #2: 9-yr-old male
VEP referral (family OD):
Fine, mostly pendular, horizontal nystagmus, photodysphoria & reduced VA: albinism?
OD: +3.00/-1.00 x /24
OS: +2.50/-0.50 x /21
Interview:
Ocular Hx:
Congenital nystagmus
Health Hx:
Unremarkable
Negative family hx of eye disease/low vision
No parental consanguinity

37. Ocular Albinism (OA) Main Features Evidence of carrier status
X-linked recessive (GPR143 mutation at Xp )
Evidence of carrier status
iris illumination
‘mud-spattered’ fundus
hypopigmented skin macules
Optometrist duties:
Strabismus Dx/Mx
Low vision care
Referral for genetic work-up
Main Features
Sl. lighter hair & skin complexion (not necessary)
Nystagmus (most horizontal & pendular)
Iris tranillumination
Macular hypoplasia
Fundus hypopigmentation
Visual pathway decussation abnormality

38. Albinism: Problem Specific Testing
Ocular Motility
Iris tranillumination
DFE
VEP
OCT (nystagmus preclude?)

39. Visually Evoked Potential (VEP)
Assess macular-cortical pathway’s gross integrity
Record
NOTE: VEP = VER = VECP (latter 2: older terms)

40. Visually Evoked Potentials (VEPs)
Types of clinical-based VEPs
Pattern: pVEP
2009 ISCEV standard
Full-field: fVEP
One example of research-based VEPs
Sweep: sVEP
No ISCEV standard yet

41. VEP Stimuli pVEP fVEP NOTE:
pVEPs can be reversing checkerboards or gratings

42. ISCEV Recording Electrodes
Scalp silver-silver chloride or gold disc surface electrodes
ISCEV standard:
1 active (3 better) plus 1 reference electrode

43. VEP Electrode Placement
International system for electrode placement
ISCEV Ref
ISCEV Active z

44. VEP Electrode Placement
Multi-channel placement
Pre-chiasmal: Better
Post-chiasmal: Required OZ

45. Measuring pVEPs
P100:
Cortical response (Amplitude in μv) to checkerboard reversal (IT: Implicit time ~100ms)
Transient VEP (<4Hz)
Amp IT

46. Simulated pVEP Normative Database (Implicit Time [ms]: 20-39 yrs)
WNL = ≤ 5th percentile
Delayed = > 5th percentile

47. Measuring fVEPs
P2:
Cortical response to 1 Hz flash stimulus (amplitude in μv; IT: Implicit time ~100ms)
fVEP useful when pVEP fails
Amp IT

48. Diagnostic Uses of pVEP
Optic nerve disease
Optic neuritis (recovery more than dx); compressive optic neuropathy; Leber’s hereditary optic neuropathy (LHON)
Post-chiasmal disease (with multiple-channels)
Demylinating disease; ocular albinism
Amblyopia
Psychogenic vision loss
Unexplained vision loss

49. Optic Neuritis

50. Visual Pathway Asymmetry
Albinism
~55% decussate
~80% decussate ++ ++ ++ + ++
+++

51. Visual Electrophysiology in Canada
Specific Locations:
UW Electrodiagnostic Clinic (Waterloo)
UM Clinique de la Vision (Montréal)
University of Ottawa Eye Institute (Ottawa)
Ivey Eye Institute (London)
HSC Visual Electrophysiology Unit (Toronto)
St. Michael’s Hospital (Toronto)
Toronto Western Hospital (Toronto)
VEP only

52. Visual Electrophysiology in Canada
Other Locations? Good question!
There is no Canadian registry for VE services
Based on existing research activity, hospital-based, university-based VE clinical services likely exist in:
Vancouver (UBC)
Calgary (UofC)
Edmonton (UofA)
Montreal (Laval & McGill)
Halifax (Dalhousie)
Other cities may also provide VE services

53. Clinical electrophysiology: Plugging into the visual system
Marlee M. Spafford, OD, MSc, PhD, FAAO