Electrophysiological techniques allow clinical investigations to include a ‘dissection’ of the visual system. Using suitable electrophysiological techniques, the ‘dissection’ allows function to be ascribed to the different photoreceptors (rod and cone photoreceptors), retinal layers, retinal location or the visual pathway up to the visual cortex. Combined with advances in genetics, retinal biochemistry, visual fields and ocular imaging, it is now possible to obtain a better understanding of diseases affecting the retina and visual pathways.

1. CLINICALCLINICAL
ELECTROPHYSIOLOGY OFELECTROPHYSIOLOGY OF
VISIONVISION
klllhh
Manish Dahal
BSc. Optm 3rd
yearMANISH DAHAL, BSc. OPTM. 3rd
YEAR

2. BELIEVE YOU CAN &
YOU ARE HALF WAY THERE

3. CASE HISTORYCASE HISTORY
 A 20 years old male presented with chief complaint of slow,
Painless progressive vison loss at distance and near. He
reported that vision was poor since 10 yrs of age and his
other symptoms was photophobia.
PATIENT HISTORY
NO any medical and family ocular history.

4. DIAGNOSTIC DATADIAGNOSTIC DATA
 VISUAL ACUITY
20/200 OU
 PUPIL was round and refractive to light
 EOM was normal
 Anterior segment was normal
 Dilated fundus revealed clear vitreous & relatively large
optic nerve with moderate size cups OU
 CONFRONTATION visual field were full to finger counting
OU

5. OD OS

6. RETINA QUIZ
1) What simple , in- office test would provide the most useful
informtaion about our patient?
a)applanation tonometry b) amsler grid
c)color vision testing ++ d) manifest refraction
2) What additional test is necessary to help confirm the
diagnosis?
a)ERG ++ b) EOG c) FA d)Visual field
3) How do you interpret the SD-OCT?
a) normal b) abnormally thick choroid
c) loss of photoreceptor integrity line ++ d) Occult
choroidal neovascularisation

7. 4) What is the most likely diagnosis?
a) Cone dystrophy++
b)Stargardt’s macular dystrophy
c) Malingering
d)Functional vision loss
DISCUSSION
The dilated fundus exam of our patient
showed essentially normal optic nerve
and a healthy macula, foveal light
reflex was present in each eye.

8. So, what was wrong with our patient??
Did he have some form of functional
visual loss or was he malingering?
The answer was embedded in case
history.
One of his complaint was photosensitivity.
He said his vision was better at night or
when the light was dimmer. He didn’t see
well in normal lighting.
CB couldn’t read 15 plates of ishihara color
vision testing

9. At this point all clue suggested that the
patient had cone dystrophy.
Cone dystrophy is acquired disorder
that affect cone photoreceptor. It
tends to be progressive in nature and
is acquired later in life –unlike other
congenital photorecptor conditions,
such as achromatopsia , nystagmus
and varying degree of color vision

10. There are several hereditary pattern of
acquired cone dystrophy- all of which
result in early loss of color vision
aswell as progressive loss in visual
acuity[ to the level of 20/200- 20/400]
In most cases vision loss begins
during teenage years, however initial
symptoms may be present in late 7th
decade. Intrestingly our patient was
first seen at the age of 15 VA being
20/60 OU

11. In our patient the retinal exam appear
normal- although we could convince
that there had been temporal optic
nerve pallor
The wide variety of clinical
presentation illustrate why
electrophysiology is so important in
confirming the diagnosis

12. ERG was performed which revealed
significantly reduced and prolonged
cone response and mildly reduced
rod response that was consistent
with an acquired cone dystrophy.
The SD-OCT is quite intresting. At first
glanCe it appears normal. However
on careful inspection, we can see PIL
is absent in fovea which suggest that
a process is affecting photoreceptor

13. There are number of hereditary pattern
for cone dystrophy including
autosomal dominant, recessive and
x- linked .
The patient family history was negative
for cone dystrophy so, it is likely that
his condition was autosomal
recessive in nature
Finally the patient was referred to low
vision service evaluation

14. The above case shows how
important is electrophysiology in
diagnostic procedure much before
than an ophthalmoscopic finding.

15. ElectrophysiologyElectrophysiology
 Electrophysiology is electrical phenomena associated
with a physiological process.
 Electrophysiology tests record the electrical
responses generated by the eyes or visual cortex
 Electrophysiology is objective test that helps in
evaluation of retinal function.

16. Common Visual Electrodiagnostic TestsCommon Visual Electrodiagnostic Tests
 ERG (Electroretinogram)
– Ganzfeld
– Pattern
– Multifocal
 EOG (Electro-oculogram)
 VEP/VER (Visual Evoked Potential/Response)
– Pattern
– Flash

17. ERG: Functional Testing of RetinaERG: Functional Testing of Retina
 A flash of light will elicit an electrical response
from the retina
 The response can be recorded by placing
electrodes on the surface of eye
 The recorded response is weak and needs to be
amplified
 Recorded data can be stored and analyzed on a
computer

18. Recording
Electrode
Amp.
Reference
Electrode
Computer
Ear
Ground
Electrode
ERG Recording Setup
Ganzfeld Dome
ERG Response

19. Typical ERG ResponseTypical ERG Response
 A-Wave: Mostly due to Photoreceptor activity (outer
retina)
 B-wave: Mostly due to On- and Off- Bipolar and Müller
cell activity (inner retina)
Scotopic 0dBFlash
-500
-400
-300
-200
-100
0
100
200
300
0 25 50 75 100 125 150
Electroretinogram
1:(µV)Od
milliseconds
B-Wave
A-Wave

20.  Full Dilatation
 30’ Dark adaptation for scotopic and 10’ light adaptation
for phototopic response
 Avoid FFA or fundus photography before ERG. If done 1
hour dark adaptation is must
 Fixation to prevent artifacts
 Connect the electrodes:
– Corneal electrodes on eyes
– Reference electrode on forehead
– Ground on ear
ERGERG:: Test ProcedureTest Procedure

21. ERGERG:: Recording ElectrodesRecording Electrodes
ERG-Jet Burian-Allen DTL
Commonly used corneal electrodes:

22.  Helps Diagnose:
– Retinitis Pigmentosa and other inherited retinal degenerations
– Congenital and acquired night blindness
– Inflammatory conditions (AZOOR, MEWDS)
– Vitamin A deficiency
 Helps Manage:
– Diabetic Retinopathy
– Central and Branch Vein or Artery Occlusion
– Monitor retinal toxicity of drugs such as Plaquenil, Quinine,
Cisplatin, Vigabatrin
 Helps Prognosis:
– Ocular trauma
– Detached Retina
ERG: Clinical ApplicationsERG: Clinical Applications

23. ERG: Additional TestsERG: Additional Tests
 Pattern ERG
– Important point: Patient need to be refracted using tri-lenses.
Use temporal fossa for reference electrode, and forehead for
ground electrode.
– Recording electrode: DTL or Gold Foil Electrode (no lens
electrode)
– Generated by retinal ganglion cells
– Glaucoma evaluation
– Macular dysfunction
 Very bright flash (+25dB) test for pre-operative
evaluation
– Dense cataract
– Vitreous hemorrhage

24. ERG: Additional TestsERG: Additional Tests
 Photopic Negative Response ERG
– Test condition: Dilated, photopic test
– Stimulus: Red Flash on Blue Background
– Generated by retinal ganglion cells
– Early glaucoma evaluation
 On/Off Response ERG
– Test condition: Dilated, photopic test
– Stimulus: Red Flash on Blue Background
– Looking at On and Off Bipolar Cells responses
– Inner retina dysfunction
 S-Cone ERG
– Test condition: Dilated, photopic test
– Stimulus: Blue Flash on Amber background
– Generated by S-Cone Photoreceptors
– Enhanced S-Cone Syndrome

25. ERG: Additional Tests - ResearchERG: Additional Tests - Research
Scotopic Threshold response ERG
– Test condition: Dilated, scotopic test
– Stimulus: Series of flash of increasing intensity
starting from below threshold (starting intensity
is species dependent)
Double Flash ERG
– Stimulus: Bright Flash followed by medium
flash

26. EOG: The Electro-OculogramEOG: The Electro-Oculogram
 Records the standing potential between the front and back
of eye
 Also called “Corneo-Fundal Potential”
 Measures function of Retinal Pigment Epithelium (RPE)
 Amplitude of potential changes with retinal illumination
over a period of minutes
– Dark: smaller potential
– Light: larger potential

27. EOG Testing: First StepsEOG Testing: First Steps
 Connect electrodes to inner and outer canthii:
 Patient looks side to side at alternating lights
 Pupil dilation and dark adaptation are not required for EOG
test
EOG electrodes

28. EOG: Recording PhasesEOG: Recording Phases
 Three phases are typically recorded in EOG
 The pre-adapt light phase is to standardize the standing
potential, taking 1-5 min.
 The dark-adapt phase is to “discharge” the standing
potential, taking 10 - 20 min.
 The light phase is to “recharge” the standing potential,
taking 4 - 10 min.
 The test takes about 30 - 40 min in total. Recording of
both eyes are recommended to save time

29. EOG: A Normal RecordingEOG: A Normal Recording
Arden Ratio: Light / Dark > 2.0 is OK

30. EOG: Clinical ApplicationsEOG: Clinical Applications
 Most commonly used in Best’s Disease (Best’s Vitelliform
Macular Dystrophy)
– ERG Normal, EOG Abnormal is CONFIRMING
diagnosis
– Abnormal EOG even in patients with no symptoms of
the disorder
 Abnormal EOG also found in:
– Retinal pigmentary degenerations
– Chorioretinal dystrophies (e.g. choroideremia)

31. VEP: Visual Evoked PotentialVEP: Visual Evoked Potential
 Measures function of visual
pathway: fovea, optic nerve,
primary visual cortex
 Pattern or Flash Stimulus
 Normally use pattern stimulus
(less variability)
– Alternating grating, sinusoid, or
checkerboard pattern
– Stimulus may be full field or
hemi-field
 Record signals at visual cortex

32. VEP: Electrode PlacementVEP: Electrode Placement
Recording
Electrode
Ground
Electrode
Reference
Electrode
Computer Amp.

33. VEP: Recording ProcedureVEP: Recording Procedure
 VEP response is very small, about 20µV or less, and
spontaneous brain activity and EMG may dominate the
individual responses
 Need to average 50-100 responses to remove noise and
reveal the underlying response
 Artifacts caused by head movements may distort the
recording, and so the sweeps contaminated with artifact
should be rejected. LKC software automatically does this.
 For Pattern VEP
– Patient should be properly refracted (near correction)
 For Flash VEP
– Must patch contralateral eye to avoid artifacts

34. Pattern VEP: A Normal RecordingPattern VEP: A Normal Recording
1
2
32x32 100%Contrast Checks2 Hz
-25
-20
-15
-10
-5
0
5
10
15
20
25
0 50 100 150 200 250
PatternVER
1:(µV)OzR
milliseconds
P100 (≅ 100 ms)

35. Pattern VEP: ApplicationsPattern VEP: Applications
 Optic Nerve Disorders:
– Optic neuropathy (compressive, ischemic)
– Optic nerve atrophy
– Compressive tumors
– Demyelinating disease (e.g., Multiple Sclerosis)
– Toxic optic neuropathies (ethambutol, cisplatin)
 Malingering, hysterical blindness
 Can use hemifield stimulation to distinguish pre-chiasmal
from post-chiasmal effects

36. Flash VEP: ApplicationsFlash VEP: Applications
 Assessing visual function behind media opacities
 Surgical monitoring
– Intraorbital surgery with risk for optic nerve damage
– Endoscopic sinus surgery

37. ConclusionsConclusions
• Visual Electrodiagnostic testing provides a way to measure
the function of the retina and the visual pathway.
• The functional examination is at the cellular level, and the
recordings can be further studied with morphological data.
• Clinical applications of visual electrophysiology are broad,
and researches are being carried out for more applications.

38. Thank You!Thank You!