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Electrophysiology in
Optometric Practice
 Introduction
 Types
 EOG
 ERG
 VEP
 Indication & Uses
 Electrophysiology is the study of electrical
properties of biological cells and tissues
 Electrophysiology examination provides
objective information in relation to visual
pathways to aid diagnosis and management
of the patient
 Assessment of functions of the visual
pathway
 Make early diagnosis
 Study potential toxicity of visual system
 Objective functional assessment &
documentation of efficacy of treatment
 Electrooculogram (EOG)
 Electroretinogram (ERG)
 Visual evoked potential (VEP)
 Examine the function of Retinal pigment
epithelium ( RPE )
 Interaction of RPE with photoreceptors ( rods)
 Eye has a standing electrical potential
 Like a ‘weak battery’
 Front of the globe is positive and the back
negative
 This resting or "standing potential" is
generated retinal pigment epithelium (RPE)
 It varies from one to several millivolts
6-10 mV
 Activation of photoreceptors also change
RPE potential
 Retinal illumination
initial rapid fall in the standing potential over
60-75 sec - "fast oscillation”
slow rise over 7-14 min - "light response" or
"slow oscillation
 Clinical electro-oculogram (EOG) measures
amplitude of the standing potential
light response
 Pre-adapted to room light levels, for at least
15 minutes prior
 Room light should be turned off and EOG
values recorded for 15 minutes
 Light stimulus turned on, and the EOG
recorded
 EOG recorded, until the light peak has
occurred and the signal amplitudes have
clearly begun to descend
 If there is no clear light peak continue for at
least 20 minutes
 Ratio of highest light point (light peak) &
lowest dark-adapted point (dark trough)
EOG Classification Ratio Range
0 Normal >2
1 Probably normal 1.80–2
2 Probably abnormal 1.60–1.79
3 Abnormal 1.20–1.59
4 Flat <1.20
 ERG is the retinal electrical potential elicited
by visual stimulation
 It is a mass response evoked by entire retina
by a brief stimulus of light
 Reflects the function of photoreceptors and
inner nuclear layers of retina
 “ rod response” ( dark adapted )
 maximal combined response ( dark-adapted)
 oscillatory potential ( dark adapted )
 single flash “ cone response “ ( light-adapted)
 30-hertz flicker response ( light adapted )
 Macular or focal ERG
 Multifocal ERG
 Early receptor potential (ERP)
 Scotopic threshold response (STR)
 Direct-current ERG
 Long-duration flash ERG (on-off responses)
 Bright-flash ERG
 Double-flash ERG
 Chromatic stimulus ERG
 Dark and light adaptation of the ERG
 Stimulus intensity-response amplitude
analysis
 Saturated a-wave slope analysis
 Both “a” and “b” waves originate in the outer
retinal layers
 “a” wave is produced primarily by the
photoreceptors
 “b” wave is produced by the bipolar cells &
muller cells
 Dark-adapted for at
least 20 minutes
 Dim white flash of
strength 2.5 log units
 Minimum interval of 2
seconds between
flashes
 Dark-adapted eye
 Interval of at least 10
seconds between
stimuli
 Response is produced
by a combination of
cone and rod systems
 Dark-adapted eye
 Flashes be given 15
seconds apart
 Only the second or
subsequent responses
be retained or averaged
 Light-adapt for at least
10 minutes
 Stimuli should not be
repeated at intervals
less than 0.5 seconds
 Light-adapted state
 Flashes be presented
at a rate of
approximately 30
stimuli per second
 Retinal response evoked by viewing usually a
black and white checkerboard or grating
 PERG is now considered to be the sum of
local luminance and pattern responses
 Provides information
regarding
-retinal ganglion function
-macula
 Advanced technology
based on the standard ERG
 Unlike single spot in
conventional ERG pattern
changes "pseudo random”
used
 In multifocal ERG you test
locally with focal
stimulation
 Focal damages can be
detected this way
 Early retinal disease
probably affect small
areas on the retina can
be detected
 Also called visual event–related potential
 Electrical activity in the visual cortex in
response to stimulation of the eye
 Visual cortex areas 17, 18, and 19 contribute
to the VEP
 Related to the transduction and transmission
of the nervous impulse from the retinal
photoreceptors to the occipital cerebral
cortex
 Disproportionately large cortical area
represents the central retina as compared
with the peripheral retina
 VEP primarily reflects central visual function,
especially overall visual acuity
 Measures the conduction of the visual
pathways from the optic nerve, optic chiasm,
and optic radiations to the occipital cortex
 Axons from the retina decussate at the optic
chiasm
 VEPs are most useful in testing optic nerve
function and less useful in postchiasmatic
disorders
 Stimulus parameters
Luminance
Pattern on-off
Pattern reversal
 Diagnosis of retinal disease
 Diagnosis of optic nerve disease
 Determination of organic versus functional
visual loss and identifying the locus of organic
loss
 Determination of visual function in nonverbal
patients
 Assessing visual system integrity behind
medial opacities
 Study of hereditary and constitutional disorders
of the retina
 Include :
partial and total color blindness (achromatopsia)
night blindness
retinal degenerations
Achromatopsia
Retinitis Pigmentosa
Congenital Stationary
Night Blindness
Retinal Vascular Disease
 Optic nerve compression (, trauma, or
subdural hematoma)
 Optic neuritis
 Optic atrophy
 Delay of the pattern reversal VEP P100
component is a useful indicator of optic nerve
disease
Optic Neuritis - LE
 ERG and/or VEP responses provide
documentation for an abnormality in either
the retina or the overall visual system
 However normal VEP in and of itself does not
rule out a visual abnormality either in higher
brain centersor in the retina
Sweep VEP
 ERGs are useful in determining general
retinal function, including whether the retina
is attached
 Focal ERGs, mfERGs, or PERGs, which can be
useful in evaluating macular function if media
are clear
 Flash VEPs, particularly with 10-Hz
stimulation, can be helpful in determining the
integrity of the visual pathways and the
normalcy of central retinal function
Electrophysiology

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Electrophysiology

  • 2.  Introduction  Types  EOG  ERG  VEP  Indication & Uses
  • 3.  Electrophysiology is the study of electrical properties of biological cells and tissues  Electrophysiology examination provides objective information in relation to visual pathways to aid diagnosis and management of the patient
  • 4.  Assessment of functions of the visual pathway  Make early diagnosis  Study potential toxicity of visual system  Objective functional assessment & documentation of efficacy of treatment
  • 5.  Electrooculogram (EOG)  Electroretinogram (ERG)  Visual evoked potential (VEP)
  • 6.
  • 7.  Examine the function of Retinal pigment epithelium ( RPE )  Interaction of RPE with photoreceptors ( rods)
  • 8.  Eye has a standing electrical potential  Like a ‘weak battery’  Front of the globe is positive and the back negative
  • 9.  This resting or "standing potential" is generated retinal pigment epithelium (RPE)  It varies from one to several millivolts 6-10 mV  Activation of photoreceptors also change RPE potential
  • 10.  Retinal illumination initial rapid fall in the standing potential over 60-75 sec - "fast oscillation” slow rise over 7-14 min - "light response" or "slow oscillation
  • 11.  Clinical electro-oculogram (EOG) measures amplitude of the standing potential light response
  • 12.
  • 13.
  • 14.  Pre-adapted to room light levels, for at least 15 minutes prior  Room light should be turned off and EOG values recorded for 15 minutes
  • 15.  Light stimulus turned on, and the EOG recorded  EOG recorded, until the light peak has occurred and the signal amplitudes have clearly begun to descend  If there is no clear light peak continue for at least 20 minutes
  • 16.
  • 17.  Ratio of highest light point (light peak) & lowest dark-adapted point (dark trough) EOG Classification Ratio Range 0 Normal >2 1 Probably normal 1.80–2 2 Probably abnormal 1.60–1.79 3 Abnormal 1.20–1.59 4 Flat <1.20
  • 18.
  • 19.
  • 20.  ERG is the retinal electrical potential elicited by visual stimulation  It is a mass response evoked by entire retina by a brief stimulus of light  Reflects the function of photoreceptors and inner nuclear layers of retina
  • 21.  “ rod response” ( dark adapted )  maximal combined response ( dark-adapted)  oscillatory potential ( dark adapted )  single flash “ cone response “ ( light-adapted)  30-hertz flicker response ( light adapted )
  • 22.  Macular or focal ERG  Multifocal ERG  Early receptor potential (ERP)  Scotopic threshold response (STR)  Direct-current ERG  Long-duration flash ERG (on-off responses)
  • 23.  Bright-flash ERG  Double-flash ERG  Chromatic stimulus ERG  Dark and light adaptation of the ERG  Stimulus intensity-response amplitude analysis  Saturated a-wave slope analysis
  • 24.
  • 25.
  • 26.
  • 27.
  • 28.  Both “a” and “b” waves originate in the outer retinal layers  “a” wave is produced primarily by the photoreceptors  “b” wave is produced by the bipolar cells & muller cells
  • 29.  Dark-adapted for at least 20 minutes  Dim white flash of strength 2.5 log units  Minimum interval of 2 seconds between flashes
  • 30.  Dark-adapted eye  Interval of at least 10 seconds between stimuli  Response is produced by a combination of cone and rod systems
  • 31.  Dark-adapted eye  Flashes be given 15 seconds apart  Only the second or subsequent responses be retained or averaged
  • 32.  Light-adapt for at least 10 minutes  Stimuli should not be repeated at intervals less than 0.5 seconds
  • 33.  Light-adapted state  Flashes be presented at a rate of approximately 30 stimuli per second
  • 34.  Retinal response evoked by viewing usually a black and white checkerboard or grating  PERG is now considered to be the sum of local luminance and pattern responses
  • 35.  Provides information regarding -retinal ganglion function -macula
  • 36.  Advanced technology based on the standard ERG  Unlike single spot in conventional ERG pattern changes "pseudo random” used  In multifocal ERG you test locally with focal stimulation
  • 37.  Focal damages can be detected this way  Early retinal disease probably affect small areas on the retina can be detected
  • 38.
  • 39.
  • 40.
  • 41.
  • 42.  Also called visual event–related potential  Electrical activity in the visual cortex in response to stimulation of the eye  Visual cortex areas 17, 18, and 19 contribute to the VEP
  • 43.  Related to the transduction and transmission of the nervous impulse from the retinal photoreceptors to the occipital cerebral cortex
  • 44.  Disproportionately large cortical area represents the central retina as compared with the peripheral retina  VEP primarily reflects central visual function, especially overall visual acuity
  • 45.  Measures the conduction of the visual pathways from the optic nerve, optic chiasm, and optic radiations to the occipital cortex  Axons from the retina decussate at the optic chiasm  VEPs are most useful in testing optic nerve function and less useful in postchiasmatic disorders
  • 46.
  • 47.
  • 48.  Stimulus parameters Luminance Pattern on-off Pattern reversal
  • 49.
  • 50.
  • 51.
  • 52.
  • 53.  Diagnosis of retinal disease  Diagnosis of optic nerve disease  Determination of organic versus functional visual loss and identifying the locus of organic loss
  • 54.  Determination of visual function in nonverbal patients  Assessing visual system integrity behind medial opacities
  • 55.  Study of hereditary and constitutional disorders of the retina  Include : partial and total color blindness (achromatopsia) night blindness retinal degenerations
  • 59.  Optic nerve compression (, trauma, or subdural hematoma)  Optic neuritis  Optic atrophy
  • 60.  Delay of the pattern reversal VEP P100 component is a useful indicator of optic nerve disease
  • 62.  ERG and/or VEP responses provide documentation for an abnormality in either the retina or the overall visual system  However normal VEP in and of itself does not rule out a visual abnormality either in higher brain centersor in the retina
  • 64.  ERGs are useful in determining general retinal function, including whether the retina is attached  Focal ERGs, mfERGs, or PERGs, which can be useful in evaluating macular function if media are clear
  • 65.  Flash VEPs, particularly with 10-Hz stimulation, can be helpful in determining the integrity of the visual pathways and the normalcy of central retinal function