lecture 5 electrical potentials 1 Flashcards
what are the 3 types of electrical recording of the eye used to diagnose ocular disease?
EOG, ERG, VEP
The front of the eye has a slight ___ charge, and the back of the eye has a slight ____ charge
positive, negative
an EOG measures the ____ difference on the eye
dipole
An EOG is efficient in diagnosing ____ disease
Best’s
what are the normal and abnormal arden ratio numbers
normal=2.5, abnormal=less than 1.9, (bests disease is typically 1.2 or 1.3)
an EOG can also be used for….
sleep studies, (very efficient at determining REM state), eye tracking technology for military or paralyzed patients.
in an EOG, where do you connect the electrodes?
temporally and nasally
what is an arden ratio?
light/dark ratio as determined by an EOG
what disease develops a patellaform (splattered egg-looking) macular degeneration often resulting in choroidal neovascularization into the retina, resulting in blindness?
Bests disease
ERG measures….
retinal current…flashing lights induce electrical change in the retina
an ERG basic waveform has what 5 parts?
a=rods and cones, b=on bipolarcells and muller cells, c=RPE, d=off bipolar cells, op’s=amacrine cells
What is an OP?
oscillitory potential, found on the upswing between a and b waves
where do the ticks of the oscillatory potential come from
amacrine cells
a device that has a forehead rest, a chin rest, and 3 gaze position holes inside a dome is called a….
ganzfeld stimulator, used as the stimulus source during an ERG reading.
which wave of the ERG waveform happens when the lights go out
d-wave
what 3 things are placed on the patient for an ERG reading?
a lens/wire placed on cornea, a ground on the ear, a reference point on the forehead
what are the 2 basic ERG measurements?
wave propagation time (implicit time) and amplitude.
a 30 Hz flicker flashes ___ times per ____
30, second
what inhibits oscillatory potentials?
glycine
what method can you use to isolate oscillatory potentials?
30hz flicker
what part of the ERG waveform represents ganglion cells?
none, you never see ganglion cell activity in the ERG waveform
name 4 classic abnormal ERG findings
complete CSNB (congenital stationary night blindness), rod monochromatism, cone dystrophy, retinitis pigmentosa
describe the ERG waveform of a patient with a retinal detachment…
nearly a flat line
true or false: ERG wave amplitudes are inversely proportional to light intensity?
true, when pt is dark adapted the amplitudes are larger.
When doing an ERG, you will want to measure photopic and scotopic, but in which order and why?
measure scotopic first then photopic, it takes less time if the patient is dark adapted first.
stargardt’s disease targets:
a) ganglion cells
b) rods
c) amacrine cells
d) cones
d) cones
An ERG reading with a flat line for the photopic 30hz flicker would be:
a) complete CSNB
b) rod monochromatism
c) cone dystrophy
d) retinitis pigmentosa
rod monochromatism, since there is no cone function with this disorder
An ERG reading with a flat line for the rod specific would occur in which two:
a) complete CSNB
b) rod monochromatism
c) cone dystrophy
d) retinitis pigmentosa
a) complete CSNB, night blindness=no rod function
d) retinitis pigmentosa=no rod function due to peripheral vision loss which travels inward leaving the very center of the macula, causing tunnel vision, and leaving only photopic vision
an ERG reading with an electronegative spike for the maximum scotopic response would occur in which:
a) complete CSNB
b) rod monochromatism
c) cone dystrophy
d) retinitis pigmentosa
a) complete CSNB
An ERG reading with a “undetectable/blink artifact” v-shaped wave for transient photopic would occur in:
a) complete CSNB
b) rod monochromatism
c) cone dystrophy
d) retinitis pigmentosa
b) rod monochromatism
ERG findings for cone dystrophy show….
normal on rod specific, moderate reduction on max scotopic responses, small and slow (decreased cone function) for photopic flicker and transient photopic.
true or false: red light enhances your mesopic vision
true, it combines light sensitivity with clarity and rods and cones work closely together in your favor. thats why a dark room (used for photo developing) has a red light.
a blue light is soley ___ response
rod
true or false: an ERG is spectrally sensitive
true, we can use different wavelengths of light to get the ERG to respond differently. (red gives a mesopic response, while blue gives a rod only response)
what is the difference between a focal ERG and a multifocal ERG?
Focal involves stimulating a small point on the retina, multifocal involves over 200 points on the retina. With multifocal, stimulus comes from an LCD screen rather than a ganzfeld.
An mfERG 3-D image with a central hole an warm colors surrounding the center describes…
Stargartds disease-scotoma in macula, loss of central retina function, looks similar to AMD, however, this will show up in younger patients.
An mfERG 3-D image with a prominent cone in center with warm colors, however, the surrounding area is blue-ish/dark describes
retinitis pigmentosa-no peripheral vision, cone is very pointy because only very central vision is left.
An mfERG 3-D image with blue-ish/green flatter plane with no central cone describes…
Best’s disease-absence of cone represents no central vision, the darker the color the lower the retinal activity. leads to blindness.
An mfERG 3-D image with incomplete central cone and normal warm colors surrounding cone describes….
AMD- incomplete cone represents macular degeneration. pt will have peripheriphal vision intact.
