The document provides information about full field electroretinography (ERG), including a brief history, the anatomy and physiology of the retina, electrode types and placement, stimulus parameters, recording techniques, waveform components and analysis. It describes the International Society for Clinical Electrophysiology of Vision standardized protocol for ERGs, including dark adapted responses to assess rod and combined rod-cone function and light adapted responses to evaluate cone pathway function. Factors affecting ERGs and guidelines for analysis and reporting of results are also outlined.
2. BACK IN TIME
• First described by Prof. E. D. Reymond who showed that
cornea is electrically positive with respect to posterior pole
of eye.
• In 1908 Einthoven & Jolly showed that a triphasic response
could be produced by simple flash of light on retina.
3. ELECTRORETINOGRAM
• ERG is the corneal measure of an action potential produced
by the retina when it is stimulated by light of adequate
intensity.
• It is the composite of electrical activity from the
photoreceptors, Muller cells & RPE
4. ANATOMY AND PHYSIOLOIGY
• The retina is organized into 10 layers comprising various cell types and synaptic connections important
for visual processing.
• The primary role of the photoreceptors is to convert light energy into an electrical signal
(phototransduction).
• The photoreceptors transmit visual information to second-order neurons known as bipolar cells in the
middle retina.
• Rods synapse only with depolarizing bipolar cells, while cones synapse with both depolarizing and
hyperpolarizing bipolar cells.
• The ganglion cells ultimately transmit this electrical information to the brain via the optic nerve. The
ratio of rods to cones in the retina is 3:1.
• These photoreceptors also vary in spectral characteristics, including signal threshold, peak wavelength
sensitivity, and rate of recovery.
6. FULL FIELD ELECTRORETINOGRAM
• ERG is the record of an action potential produced by the retina
when it is stimulated by light of adequate intensity.
• A small part of the current escapes from the cornea, where it can
be recorded as a voltage drop across the extracellular resistance,
the ERG.
• The full-field electroretinogram (ffERG) is an test that provides
non-invasive objective quantitative measures of the electrical
activity in the retina.
• The ffERG represents an electrical response from the retina to a
flash of light and measures global retinal function.
7. RECORDING SIGNALS FROM RETINA
• Full field electroretinogram measures ;
Mass response of retinal cells to a light stimulation
Electrical response in the retina occurs due to light induced
changes
Measured by placing electrodes
These signals are very small µV( even after amplification)
8. INDICATIONS
The ffERG is a specialized test beyond standard ophthalmologic
examination. Electrophysiologic testing may be indicated in the following
scenarios:
• Diagnose and follow optic nerve and retinal diseases
• Monitor retinal disease from toxic drug exposure
• Assess intraocular inflammation
• Evaluation of the construct of intraocular foreign bodies
• Evaluation of retinal vascular occlusions and associated ischemic
damage
• Evaluation of malingering or hysteria
9. INDICATIONS
• Aids in diagnosis of stationary or progressive inherited
retinal disorders
• Asess patients with retinal toxicity due to metallosis(
Siderosis)
• Asess retinal toxicity to medication
• Document therapeutic effect of surgery or medication
ERG results are normal unless more than 20 % retina is
affected
12. WAVEFORM COMPONENTS
a-wave
The a-wave is the initial negative deflection corresponding to the early
hyperpolarization of the rod and cone photoreceptors.
This wave-component reflects outer retinal function.
b-wave
The b-wave is the positive deflection following the a-wave that originates from the
depolarization of inner retinal Muller and bipolar cells.
This wave-component reflects phototransduction activity.
13. • Oscillatory potentials
Oscillatory potentials (OPs) are high-frequency rhythmic
wavelets seen on the rising slope of the b-wave. OPs are visible at
greater signal intensities and reflect the electrical activity of inner
retinal feedback synaptic circuits, namely amacrine cells, as well
as some vascular function.
• Photopic negative response
The photopic negative response (PhNR) is the light-adapted,
negative deflection that follows the b-wave. It originates from the
retinal ganglion cells in response to a brief flash.
14. WAVEFORM ANALYSIS
Amplitude
The amplitude is the maximal light-induced electrical response (voltage) generated by the
various retinal cells.
Implicit time
Implicit time (time-to-peak) refers to the time needed for the electrical response to reach
maximum amplitude.
Latency
Latency is the time from stimulus onset to response onset, as opposed to the peak of the
response (i.e., implicit time).
15. • We need ;
Light stimulation
Calibrated stimulus
Electrodes
Amplifier and signal averager
Display monitor and printer
16. LIGHT STIMULATION FOR ERG
Several methods of stimulating the eye;
• Strobe lamp and LEDs that is mobile and can be easily placed in front of a
person whether sitting or reclining
• Ganzfeld (globe) with a chin rest and fixation points (german word –whole
field)
• Grass xenon arc photostimulator
• Ganzfeld allows the best control of background illumination and stimulus
flash intensity and fixation lights.
• Large diameter ( 40 cm ) hemispheric dome with xenon stroboscopic light
bulb placed at the top of the dome.
17. STIMULI
Full field stimulators and light diffusion
• Ganz Feld provides dispersed light and uniform luminance over the maximal
area of retina.
• A central fixation spot should be provided.
• Stimulators should allow observation of the patient to monitor fixation and other
factors that may influence recordings e.g., electrode position, eye closure,eye,
face and head movements.
• Ganzfeld stimulators may be large enough to stimulate both eyes simultaneously
for two channel recordings, or a small (mini) ganzfeld can be used for sequential
stimulation of each eye
• For sequential testing care is needed during stimulation to ensure that light is
excluded from the opposite eye.
18. Stimulus duration
• shorter than integration time of photoreceptor < 5 ms
Stimulus wavelength
• Flashes and background should be visibly white
• Historically, light stimuli specified by ISCEV were generated by xenon
flashtube, superseded by light emitting diode (LED)technology.
Stimulus strength and unit
• Stimulators should be capable of flashes over a minimum range of 3 log units in
strength, in steps of not more than 0.3 log units.
• Background luminance for light adaptation and LA ERG testing is specified in
candelas per meter squared (cd.m-2)
• Flash stimuli in units of candela-seconds per meter squared (cd.s.m-2)
Nomenclature
Stimulus and background callibration
19.
20. ELECTRODES
Important features of ERG recording electrodes include
1. Quality components with low intrinsic noise levels, which facilitate stability of
responses
2. Patient tolerance, with limited irritation of the corneal surface
3. Availability at a reasonable cost
• Ground electrode – Forehead Earlobe Mastoid connected to ground input
• Reference electrode-Outer canthus or zygomatic fossae, connected to – input of
recording system
• Active electrode- Cornea( contact lens electrode) in flash ERG
- Conjunctival sac in pattern ERG
or skin on lower eyelid, connected to + terminal
21. CORNEAL ELECTRODES
Hard contact lenses that covers sclera such
as-Burian allen electrode
• Doran gold contact lens
• Jet electrode (disposable)
FILAMENT TYPE
• DTL fibre electrode(Dawson-trick-
Litzkow)
• HK loop electrode
• Gold foil electrode
22. Burian allen
electrode
•Advantage of a lid speculum
• Electrode consists of an annular ring of stainless steel surrounding the central PMMA contact-Iens core
•Bipolar version of the Burian-Allen lens, a conductive coating of silver granules suspended in polymerized plastic is painted on the outer surface of
the lid speculum serving as a reference electrode
DTL electrode
•Mylar thread whose individual fibers (approximately 50 pm in diameter) are impregnated with metallic silver.
•amplitudes of the ERG responses recorded with the DTL electrode are, on average, reduced 10% to 13%.
Jet electrode
•made of aplastic material that is gold-plated at the peripheral circumference of its concave surface.
• Its advantages include sterility, simplicity in design, and ease of insertion, which has potential benefit for sensitive eyes.
23. Hk electrode
• The Hawlina-Konec loop electrode is noncorneal electrode, consisting of a thin metal wire (silver, gold,
or platinum) molded to fit into the lower conjunctival sac
Skin electrode
• Recording ERGs from infants and young children,the corneal electrode can be replaced by an electrode
placed on the skin over the infraorbital ridge near the lower eyelid.
• Recorded amplitudes are 10 to 100 times smaller than those obtained using a corneal electrode.
• Screening purpose
24. ELECTRODE CLEANING
• Recording ERGs involves the exposure of corneal electrodes to tears, and
there is potential exposure of skin electrodes to blood if there is any break in
the surface of the skin.
• Reusable electrodes must be cleaned and sterilized after each use to prevent
transmission of infectious agents.
• The cleaning protocol should follow manufacturers’ recommendations and
meet current local and national requirements for devices that contact skin
and tears
• Impedance should be less than 5 kohm
• In the absence of light stimulation and eye movement, the baseline voltage
should be stable
25. RECORDING AND AMPLIFICATION
• The elicited response is then recorded from the anterior
corneal surface by the contact lens electrode
• The signal is then channeled through consecutive devices
for pre-amplification, amplification & finally display.
26. Real time display
• The ongoing recordings should be displayed during testing so that the operator can
continuously monitor technical quality and stability, and make adjustments as
necessary.
Recording and storing ERG data
• Digital records of all ERGs should be stored. Ideally, these should be records of
individual ERG waveforms rather than averages only, which may be distorted by
artefact.
Averaging
• Averaging may be essential to identify and measure pathologic ERGs of low
amplitude or ERGs recorded from electrodes on the lower eyelid.
• Artefact rejection must be a part of any averaging system
27. READING PROTOCOL
Full pupillary dilation
20 minutes of dark adaptation
(DA)
Rod response
Maximum combined response
Oscillatory potentials
Light adaptation (10 -15 mins)
Single flash cone response
30 Hz flicker
28. Pre exposure to light –
• FFA,Fundus photos avoided, OCT , imaging avoided
• 30 min recovery time if exposed
• DA -20 min
• LA- 10 min
• Fixation
• Looking at the fixation point
• Eye movements alters electrode position
• Straight ahead and steady eyes if cant see fixation point
• For non contact electrode gentle blinking before each
flash may reduce artefacts
Pupillary dilation and retinal
illumination
29. ISCEV STANDARD ERG PROTOCOL
• International society for clinical electrophysiology of vision
• Standardized the protocols for preforming electrophysiological tests (1989)
30.
31.
32. Dark adapted 0.01 ERG Rod driven response of bipolar cells ,a – rods
b- bipolar
Dark adapted 3 ERG Combined rod- cone response arising from
bipolar cells and photoreceptors a –rod+ cone ,
b –bipolar
Rod dominated
Daark adapted Oscillatory potentials Responses primarily from amacrine cells
Dark adapted 10 ERG Combined response with enhanced a wave
reflecting photoreceptor function
Light adapted 3 ERG Cone driven response of bipolar cells a- cone ,
bipolar cells
Light adapted 30 Hz flicker ERG Sensitive cone pathway driven response a- cone
33. DARK ADAPTED 0.01 ERG
(ISOLATED ROD RESPONSE IRR)
• Minimum 20 minutes dark adaptation
• Phot 0.01cd.s.m2 or scot 0.025 cd.s.m2
• Retina stimulated with dim flashlight of 2.5 log units 24 db
• Flash white or blue
• Resultant waveform has prominent b(positive) wave but no detectable a
(negative)wave
• Minimum 2 secs interval between flashes
34. DARK ADAPTED 3 ERG
MAXIMAL COMBINED RESPONSE (MCR)
• Directly following 0.01 ERG
• Response produced by combination of rods and cones
• Large a wave and b wave amplitude
• OPs on b wave
• 10 secs interval between stimuli ( to remove effect of
bleach)
• Phot 3cd.s. m2, scot 7.5cd.s.m2
35. DARK ADAPTED 10 ERG
• Combined with enhanced a wave for photoreceptor
function
• DA 10 a- wave is larger having shorter peak time consistent
with greater rod photoreceptor contribution
• Interval of 20 secs between stimulus
• Enhanced OP compared to DA3 ERG
• b-wave to a-wave amplitude ratio smaller than for the DA
3 stimulus
• phot 10 cd.s.m2, scot 25cd.s.m2
• DA10 ERG maybe more informative than ERGs to dim
flashes in patients with opaque media, small pupils or
immature retinae
36. DARK ADAPTED OP
• Generated by amacrine cells
• can be measured using both 3 or 10 cd.s.m2 flash stimuli
• On ascending limb of b wave of maximal combined
response
• Other wavelets removed by resetting of filter to eliminate
lower frequencies from dark adapted 3 ERG
• Band pass filter on amplifier set between 75 to 300 Hz to
get these wavelets
• Sensitive to ischaemia in localized retinal areas.
37. LIGHT ADAPTED 3 ERG
(SINGLE FLASH ERG)
• 10 min light adaptation
• Measure of cone system
• Phot. 3 cd.s. m2 stimuli
• 0.5 sec interval between successive flashes on light
adapting background luminance 30 cd/m2
• Has smaller a –wave and b –wave
38. LIGHT ADAPTED 3 FLICKER ERG
• Repetitive stimuli flickered at rate 30 Hz superimpose on
light adapting background luminance 30 cdm2
• Rod theoretically respond to stimulus up to 20 HZ so
screens out –gives Cone activity
• Interval of stimulus > 5 ms
• A flash presented close to 30Hz, superimposed on a light-
adapting
• Generated largely by cone On- and Off bipolar cells
• Dependent on the function of the long- and medium-
wavelength sensitive cones (M- and L- cones)
39. OTHER FACTORS AFFECTING ERG
• Light stimulus
• Drugs
• Retinal development
• Media clarity
• Age , sex and refractive error
• Anesthesia
• Diurnal fluctuation
40. ANALYSIS AND REPORTING
Amplitude
• a wave measured from the baseline to the trough of a-wave.
• b wave measured from the trough of a-wave to the peak of b-wave.
Time sequences
Latency:-
• Time interval b/w onset of stimulus & the beginning of the a-wave
response. Normally it’s 2 ms.
• Implicit time:- time from the onset of light stimulus until the maximum
a-wave or b-wave response.
• Considering only a-wave and b-wave response the duration of ERG is
less than 1/4 s
41. In single flash erg
• The peak times will depend on flash duration if measured from the beginning of the stimulus
flash.
• Small effect when the stimulus duration is less than a millisecond and can be ignored, for
example, when stimuli are generated by a xenon flashtube.
• For longer flashes of up to 5 ms, such as those generated by LEDs, the time to peak should be
measured from the midpoint of the flash, or half the flash duration subtracted from the peak
time, to compensate.
There are typically three main positive OP peaks, often followed by a fourth peak that is smaller.
• For routine applications, the presence and waveform of the OP peaks and their normality
relative to appropriate reference data may be adequate for most clinical applications.
• Quantification is optional, but if used must specify the filter characteristics and measurement
methods e.g. individual peak amplitudes measured from their preceding troughs or a sum of
amplitudes of specified peaks.
42. • The response to the initial onset of the flicker, which may
resemble a single-flash ERG, should always be excluded.
• The peak time of the flicker ERG is measured from the
midpoint of the stimulus flash to the following peak
• (avoiding the initial waveform).
• Abnormality of waveform shape should be described (e.g.
a double-peak waveform), and the components that are
measured clearly identified.
43. ANALYSIS AND REPORTING
• Each laboratory should have its own normative values for
the equipment
• Rods more affected
• Cones more affected
• Both rods and cones affected
• Negative waveform
44. NORMAL ERG
• Localized macular dysfunction
• Optic nerve disease
• Central nervous system disease as amblyopia
45. SUBNORMAL ERG
• Amplitude of all components are reduced approximately to same degree
• Early stages of rod cone dystrophy
• PRP for diabetic retinopathy (b/a ratio normal )
• Vitreous hemorrhage (ERG+ USG) can be used in differentiation of TRD and
dense vitreous
• SF6 and silicone oil
• Partial or sectoral retinal detachment
46. NEGATIVE ERG
• Amplitude of b wave smaller than that of a wave
• ba ratio < 1
• Normal a wave with reduced b wave – defect to post
synaptic phototransduction process
• Negative erg is useful prognostic and diagnostic value in
retinal disease
• CRAO , CRVO
47. EXTINCT ERG
• Advanced stage of rod cone dystrophy
• RP
• TRD
• Gyrate atrophy
• Choroidermia
• Ophthalmic artery occlusion
• Retinal aplasia
• Even when macular area is preserved ERG may become undetectable.
50. • Associations to RP
• Lawerence-moon-biedl syndrome
• Usher syndrome
• Refsums syndrome
• Pigment in retina is prominent in many
infectious disease . Early stages of rubella and
syphilis can mimic fundus appearance of RP.
• ERG is normal or slightly subnormal in this
infectious disease.
51. EARLY RECEPTOR POTENTIAL IN RP
• In a study
- small ERP amplitudes in the affected boy and the carrier women with sex-
linked retinitis pigmentosa
- less than 20 % of normal reduction in affected , 50 % reduction in carrier
- defect exists in the outer segments of the photoreceptors
- Decreased amplitude may be due to decrease in visual pigment
concerntration, no. of photoreceptor, disorientation of outer segment
membranes .
- carrier females had rapid ERP recovery during dark adaptation suggesting
that the cone visual pigments generate much of this response.
52. CONE-ROD DYSTROPHY
Patients with cone-rod dystrophy typically
show reduced visual acuity, color vision
deficits, visual field impairment (including
central or paracentral scotomas,
midperipheral partial or complete ring
scotomas, or peripheral restriction), and
reduced ERG-
cone and rod amplitudes
Cone-rod
dystrophy is a genetically heterogeneous
condition, with autosomal dominant, autosomal
recessive, and X-Iinked recessive modes of
transmission occurring.
58. OGUCHIS DISEASE
Rod receptor dysfunction
AR
Photopic normal , scotopic decrease in amplitude
-ve ERG with high luminance
Yellow phosphorescent discoloration in peripheral retina
59. FUNDUS ALBIPUNCTATUS
• Presence of numerous discrete dull-white spots scattered
throughout the fundus, with the exception of the fovea
• Cone and rod adaptations follow a prolonged time course of variable
severity, ranging, for the rods, from approximately 45 min to several
hours.
• Mutations in a gene encoding ll-cis retinol dehydrogenase
• Reduced activity of this enzyme would appear to account for the
delay in regeneration of cone and rod visual pigments observed in
this disease
• Rod ERG absent after 30 min dark adaptation
• Normal after 3 hours of dark adaptation
• Combined response –ve after 30 mins normal after 3 hours
62. STARGARDT MACULAR DYSTROPHY
• Full field ERG is normal except at very late stage where it
becomes subnormal
• Macular multifocal is dramatically abnormal
63.
64. BEST MACULAR DYSTROPHY
• ERG
cone and rod a- and b-wave amplitudes are
typically normal in patients with Best
vitelliform macular dystrophy.
68. Choroidal atrophy
• AD, AR
• ERG is subnormal, becoming nondetectable with more advanced disease.
Gyrate atrophy
• AR
• Patients are frequently myopic, and nearly all develop posterior subcapsular lens
opacities
• ERG cone and rod amplitudes are usually either markedly reduced or non
detectable
• Choroidermia
• Recordings show a reduction of a- and bwave amplitudes under light- and dark
adapted test conditions, with the prolongation of both rod and cone b-wave implicit
times.
• X linked recessive
•
72. CENTRAL RETINAL ARTERY OCCLUSION
Decreased b-wave amplitude and
diminished or nondetectable OPs accompany central
retinal artery occlusion (CRAO)
A wave- choroidal blood supply to outer retina
Inner retina supplied by CRA
Negative wave can also be seen.
73. CENTRAL RETINAL VENOUS OCCLUSION
• Ischemic CRVO usually shows negative response than non
ischemic
• For prognosis b/a ratio to be seen
74. • In branch artery occlusion (BAO), there is generally either a slight b-wave
reduction or a normal ERG response.
• Sickle cell retinopathy
-ERG a-wave, b-wave, and OP amplitudes were found to be normal in the
absence of peripheral retinal neovascularization and reduced in amplitude when
peripheral retinal neovascularization was present.
• Carotid artery occlusion
-ERG a- and b-wave amplitudes depends on the extent and severity of the
occlusion, its location.
-With occlusion of the internal carotid artery, a reduction in both a and b-wave
amplitudes can be found.
Ophthamic artery occlusion results in unrecorable ERG.
76. CHLOROQUINE AND HYDROXY
CHLOROQUINE
If the changes are clinically
apparent only in the macula, the ERG is
usually normal or occasionally subnormal to
a small degree.
With more advanced and
extensive disease, when peripheral pigmentary changes
also become apparent, the ERG is usually moderately
subnormal, while nondetectable or minimal responses are
obtained
in patients with advanced retinopathy.
Multifocal ERG is best for drug toxicity.
77. • The case of a 38-year-old man who, during the use of
indomethacin, noted a deterioration of showed a reduced
scotopic ERG b-wave amplitude .
• Quinine
-Transient subnormal ERG response of both a and b-wave
amplitudes is apparent if testing is done within the first 12 to
18 hours,
-ERG is most frequently normal when recordings are
obtained after 24 hours in acute quinine poisoning.
78. VITAMIN A DEFICIENCY AND RETINOIDS
• Scotopic responses in patients with vitamin A deficiency.
• Subnormal-to-nondetectable responses were noted in
patients with xerosis and night blindness.
• Reduction in ERG amplitudes most apparent under scotopic
conditions with prolonged use of retinoids.
79. OPTIC NERVE AND GANGLION CELL
DISEASE
• Because the ganglion cells do not contribute to the flash-
elicited full-field ERG response, an essentially normal ERG
is obtained in most eyes blinded by glaucoma.
• ERG recordings have been reported in patients with optic
nerve hypoplasia.
• The majority of these patients showed normal photopic and
scotopic ERG amplitudes.
80. OPAQUE LENS OR VITREOUS
• Dense lens opacities can reduce the ERG a- and b-wave
amplitudes. When present, the amplitude decrease is associated
with a comparable increase in implicit time, relating to the
resultant decrease in effective stimulus intensity.
• Lens opacities do not appear to modify the OPs.
• With longstanding vitreous hemorrhages, a marked reduction of
ERG amplitudes is always possible because of the ever-present
threat of siderotic changes occurring within the retina secondary
to blood-breakdown products.
81. DIABETIC RETINOPATHY
• The most frequently reported ERG abnormalities in patients
with diabetic retinopathy include a reduction in b-wave
amplitude and a reduction or absence of Ops
• Reduced OP amplitudes have been noted at early stages of
retinopathy, when ERG a- and b-wave amplitudes are
normal, while delayed OP implicit times have been reported
as an early functional abnormality in eyes with mild or
even no retinopathy.
82. • If PDR is present with vitreous hemorrhage, it is difficult to predict outcome after vitrectomy .
Having undergone PRP ERG ,
• amplitude decreases
• b/a ratio is normal
• b/a ratio provides useful prognosis after
Vitrectomy.
83. • The amplitudes of both a- and b-waves are related to the
degree of retinal detachment.
• Karpe and Rendahl have reported subnormal ERG values
in the normal eye when the contralateral eye has a retinal
detachment.
• Extinguished ERG in TRD
RETINAL DETACHMENT
84.
85. Silicone oil and sulfurhexafluride gas
• In the early postoperative period, a reduction of both a- and b-wave amplitudes
which recovers later.
• Because resistance of vitreous increases by several folds causing reduction in current.
Hyperthyroidism – thyrotoxic exopthalmus
• Supernormal ERG response due to increased bioelectrical activity
Myxedema – subnormal response
Parkinson disease- subnormal scotopic and photopic response
Myopia-
direct correlation between the amplitude of the b-wave and the degree myopia, with
patients who have approximately 7 diopters or more of myopia already manifesting
subnormal b-wave amplitudes
In absence of degenerative myopic fundus normal ERG
With degenerative myopic fundus -75% have subnormal ERG 25% have normal
ERG pattern in patients with myopia is either negative or markedly reduced in
amplitude, the myopia may be associated with an inherited retinal disorder like CSNB
or RP.
86. ERG IN MYOPIA
• Several studies have shown that ERG amplitudes are
inversely proportional to axial length.
• While all myopic eyes had a- to b-wave amplitude ratios
that were within normal limits despite generalized
amplitude reductions, hypermetropic eyes had a- to b-wave
amplitude ratios that were either subnormal, normal, or
hypernormal
87. ERG IN MULTIPLE SCLEROSIS AND
DEMYELINATING OPTIC NEURITIS
• Decreased b wave amplitude in the affected eye.
• These results provide neurophysiological evidence that
retinal damage is not due to loss of myelin but is an early
feature of demyelinating optic neuritis.
• This damage preferentially affects the retinal elements
associated with the generation of the 'b' wave of the ERG,
probably the glial cells of Müller.
88. INTRA OCULAR FOREIGN BODY
The time and rate of ERG changes associated with the retention of an
intraocular foreign body depend on
1. The nature of the metal (its alloy content)
2. The degree of encapsulation
3. The size and location of the particle
4. The duration within the eye
Iron and copper affect rapidly whereas aluminum doesn’t
When metal is in anterior segment or lens there is no significant change in ERG
response.
The ERG changes induced by the foreign body pass through the stages of a
transient supernormal response, a negative positive response, a negative-
negative response, and, finally, a no detectable response.
89. PHOTOPIC NEGATIVE RESPONSE
• The photopic negative response (PhNR) is a negative going wave seen after the
b-wave in a brief-flash photopic (cone) ERG.
• PhNR, particularly when elicited by a red flash on a rod saturating blue
background, is believed to originate primarily from retinal ganglion cells
(RGCs).
• When a long-duration flash is used the PhNR is seen once after the b-wave
(PhNR-ON) and again as a negative going wave after the d-wave (PhNR-OFF).
• The PhNR-ON and PhNR-OFF are thought to reflect the activity of the ON- and
OFF-RGC pathways respectively.
90. • Studies attempting to correlate PhNR amplitude loss with structural or functional
losses in the RGC complex and/or nerve fiber layer show that central RGC losses
produce significant amplitude losses in the focal PhNR, but not always in the full-field
PhNR.
• On the other hand, diffuse or peripheral RGC losses show more prominent
attenuation of the full-field PhNR amplitude.
• Despite the fact that the full field and focal PhNR are being used clinically in the
diagnosis and monitoring of glaucoma and other diseases the assumption that a given
reduction in PhNR amplitude corresponds with a similar reduction in RGC cell count
is questionable.
91.
92. Extinguished
d ERG
Supranorma
l ERG
Subnormal
ERG
Negative
response
Attenuated
OP s
TRD Siderosis
bulbi
Hypothyroid
ism
CRAO
CRVO
CRAO ,
CRVO
Retinal
aplasia
Hyperthyroi
dism
Chloroquine Retinoschisis Diabetic
retinopathy
Severe RP Oguchi CSR
Lebers
congenital
amaurosis
Hypertensiv
e
retinopathy
Ophthalmic
artery
occlusion
93. REFERENCES
• Electrophysiological testing in disorders of retina, optic
nerve , visual pathway , 2nd edition
• ISCEV guides to visual electro diagnostic procedures
• Various internet sources
•
