This document discusses various electrophysiology techniques used in optometric practice, including electrooculography (EOG), electroretinography (ERG), and visual evoked potentials (VEP). EOG measures the electrical potential of the retinal pigment epithelium and is used to diagnose retinal diseases. ERG records the retinal response to light and evaluates photoreceptor and inner retinal layer function. VEP detects the brain response to visual stimuli and assesses the visual pathway and cortex. These objective electrophysiology tests provide information to diagnose conditions, monitor treatment effectiveness, and study the visual system.

1. Electrophysiology in
Optometric Practice

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)

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

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

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

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

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

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

48.  Stimulus parameters
Luminance
Pattern on-off
Pattern reversal

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

56. Achromatopsia

57. Retinitis Pigmentosa
Congenital Stationary
Night Blindness

58. Retinal Vascular Disease

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

61. Optic Neuritis - LE

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

63. Sweep VEP

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