Electrophysiology Flashcards
ECG
electro-cardiogram; heart; spontaneous
ERG
electroretinogram; retina, light induced
EOG
electro-oculogram; eye; standing potential
EEG
Electro-encephalogram; brain; spontaneous
VEP
Visual evoked potential;
AEP
Auditory evoked potential;
SEP
Somatosensory evoked potential;
ERP
Event related potential
Full-field flash ERG
recording of the electrical field generated by the retina in response to abrupt changes in light; electrical field changes when light alters the dark current and induces changes in neural activity within the IPL and OPL
A-wave
flash interrupts the dark current (generated by photoreceptors)
-initial dip in graph-
B-wave
neural activity within the IPL and OPL (may primarily reflect bipolar cell activity)
-steep climb in graph-
Oscillatory potentials
lateral interactions between cells
- steps in steep climb/b-wave-
Extinguished
No ERG to any stimulus
Diminished
dama
pan-retinal photocoagulation
found in diabetic retinophaty
normal dark-adapted, absent light-adapted ERG
no cone function (monochromacy)
normal A-wave, abnormal B-wave
dysfunctional bipolar cells “negative ERG”
ex. congenital stationary night blindness, X-linked retinoschesis
progressive abnormalities
ERG loss may precede functional loss - gradual reduction in ERG response.
ex. retinitis pigmentosa, retinal dystrophies, melanoma associated retinopathy, carcinoma associated retinopathy
outer retinal function
a-wave
middle retinal function
b-wave
PERG
pattern electroretinogram
the electric field generated by the retina to a pattern - no average luminance
glaucoma test
PERG
PERG testing which cells
amacrine and ganglion
standard PERG clinical steps
checkerboard, no dilation, let patient blink, average of 150+ readings
mfERG
multifocal ERG: identifies and/or monitors regional dysfunction in the retina,
m-sequence
pseudorandom, checking different portions of retina
electro-oculogram physiological basis
tight junctions
RPE and outer photoreceptor
standing potential of eye (EOG)
measured by eye movement
standard EOG
alternate fixation +/- 15 degrees, record 10 saccades each minute
arden ratio
light peak/dark trough
normal range 1.4 - 3.0
is EOG sine wave or square wave
square wave, ignoring titers (inaccurate fixation/overshoots and blinks)
EOG more shallow/but faster
Best’s disease
VEP
visual evoked potential - part of the electroencephalogram from the visual cortex that is associated with vision
physiological basis of VEP
visual responses can be recorded because they are time-locked to a visual stimulus - ion
VEP represents….
macula/acuity
ERG represents….
widespread retinal loss
percent of retinal area is the macula
5 percent
percent of visual cortex that processes macular function
80 percent
pattern VEP
more sensitive, less variable, require fixation and resolution
VEP maturation
transmission time (stimulus to processing stimulus) reduces between birth and 4 months
optimal VEP pattern at birth
bright flash or large pattern
optimal VEP pattern for adults
small checker
Delays in VEP amplitudes
indicate dysfunction of macular pathway
Smaller checks
longer peak latenciy
lower contrast
longer peak latency
standard VEP set-up
active electrode on occipital scalp and reference electrode on frontal scalp
clinical application of VEP
evaluation of macular pathways, assessments of visual pathway routing,
albinism
visual route defects due to melanin defect
can binocular detect monocular defects in VEP?
no - can only detect after monocular
