Electrodiagnostics Flashcards
Symptoms of Balint’s?
Simultagnosia - bilateral issues; spatial neglect
(only see that one object)
Oculomotor Ataxia - Sporadic eye movements make hand-eye coordination difficult
Effects accom, vergence, parallax, etc
Oculomotor Apraxia - 2* to ataxia. Hard to fixate/saccade
Causes of Balints
Most common Alzheimers
Damage of bilateral occipital damage at angular gyrus
TIA
Perinatal hypoxia
Creutzfeld-Jakob
Iatrogenic (Nitroglycerin)Diagnosing of Balint’s
VAs
VFs: Small field of attention
Pursuits and saccades - EOMs
Cookie thief picture
Where are the electrodes placed for EOG
Canthus on measured eye - lateral and medial- and on forehead or earlobe (ground)
What’s the resting potential of the eye using EOG
6mV light
3mV dark
What’re sources of voltage of the eye?
Cornea
RPE/Photoreceptors
Muller Cells
What accounts for the difference in light and dark potentials in EOG?
The RPE hyperpolarizes to light. Larger difference between cornea and retina. Larger number in the light
How long does it take to get to light rise?
10-15 mins
How long does it take to get to dark trough?
8 minutes
What’s the Arden ratio?
Arden ratio = Light rise:Dark trough
What’s the normal range of Arden ratio?
180% - 250%
Smaller = ill eye
Larger than 300 = lacking pigment eye
Albino
What can the EOG measure?
Defects of the entire eye (only gets very gross potentials)
Ex: Will get Leber’s but will miss retinal tear
How do you measure the EOG? (The procedure)
Put electrodes on pt’s canthi.
Have patient follow red spots and sounds with eyes moving 30 degrees each swing
Measure dark current first. Measure 10 swings every 30 seconds and check current
Dark current takes 8 minutes!
Turn the lights on and wait 15 minutes to do same with light peak
When would an EOG get an inaccurate measurement?
Electrodes slide
Unsteady gaze/pupil size
Malingering and looking away/closing eyes
Which parts of eye are the light insensitive part of the EOG? (Dark trough)
Retina, Lens, Cornea
Damaged retina = decreased EOG
What parts of the eye are the light sensitive part of the EOG? (Light peak)
Intact Retina
Photoreceptors
Entire INL
True or false, retinitis pigmentosa is a genetic disease
True
What type of genetic disease is RP?
Xlinked recessive
Potential visual fields of RP pts?
Ring scotoma
Tunnel vision
Island of vision
What does EOG of RP look like?
High threshold, no rod/cone break. Imagine the rod cone break curve without the rod part obvi
What part of visual field does RP affect?
Superior field. Inferior retina more affected because top lid covers superior retina
What does RP do to damage the retina?
Doesn’t recycle photopigments. Left behind in periphery and scars/makes bone spicules. Can have pts wear sunglasses to fix it
When’s the rod/cone peak time?
10 minutes
When do you reach threshold for the rod/cone peak?
25 minutes
What’s Usher syndrome?
RP and deafness
Just like the real Usher
Also hereditary
What’s siderosis bulbi?
Foreign body got in eye and left rust ring
Rusty eye is the affected one
Best (aka Vitelliform) disease has what inheritance pattern
Autosomal dominant
What would you see in the OCT
Space in the macula. May or may not affect VT
Bands of layers may not appear smooth and uniform
What are the stages of Best’s Disease
Previtelliform Vitelliform Pseudohypopion Vitelliruptive Atrophic
Describe Previtelliform stage of Best’s
A little yellowish but very difficult to tell otherwise
Describe Vitelliform stage of Best’s
Egg yolk appearance. Usually in macula but can be multifocal. The surrounding fundus is usually normal
Describe Pseudohypopyon of Best’s
Boat shaped cyst usually on macula. May or may not affect VAs. Stage usually found in teenagers. Fluid has broken through RPE. Can see as a gap in macular lesion. Fluorescein may also show leakage.
Arden ratio is low
Describe Vitelliruptive of Best’s
Scrambled egg appearance.
VAs finally low here for sure
May note pigment clumping and atrophy
Describe Atrophic stage of Best’s
Scarring occurs. Pigment.
VAs horrid
What diseases can be visualized using EOG
Best's vitelliform
Retinitis Pigmentosa
Siderosis bulbi
Stargardt's
Plaquenil (AKA hydroxychloroquine) retinopathy
Bullseye retinopathyWhat’s a key sign of Plaquenil retinopathy?
Flying saucer sign in macula on OCT
How would you set up an ERG?
Proparicaine or SCL the target eye
Put DTL electrode on an eye (one part each side of canthus and thread btw them over the cornea)
Flash light in eye
Photoreceptors, RPE and Muller cells will react
What’s the ERG effectively testing?
Objective Visual Field
For Flash/full field ERG, compare photopic and scotopic waves and why are they like this?
Photopic waves faster and smaller. Only cones acting
Scotopic is slower and larger because accounts for summation of all the rods and cones. Remember that rods are 20:1 to cones in retina. Way larger signal
What is the Early receptor potential and what’s it associated with?
Flash of light at 30 Hz, short delay before signal detected. Caused by uncoupling of photopigment. Not used clinically because light needs to be extremely bright
Part of the Flash/full field ERG
What makes the flash/full field ERG wavepattern?
Early receptor potential (ERP) seen by outer retina (The cones!)
Explain the A, B and C waves of the ERG
A wave is the 1st dip. Caused by hyperpolarizing of photoreceptors after being exposed to the light
B wave is the peak that comes after. Positively charged due to the sending of signals from bipolar cells and activity of muller cells
C wave is the peak that comes a little later due to the sloughing of photopigments. Only happens after long amounts of illumination
What kind of ERG utilizes squarewave stimuli?
Flash ERG
What kind of stimuli do Flicker ERGs require?
Squarewave stimuli
Flashes at 30 Hz (outside of rod CFF of 20hz. Rods can’t see)
What kind of Waves do Flicker ERGs detect?
Series of B waves (looks just like a sine wave going on)
What kind of defects do Flicker ERGs detect?
Damage to outer retina
For example, diabetes
What causes the flicker ERG in the retina?
Bipolar and muller
What kind of damage is seen with the pattern ERG? (PERG)
Damage to inner retina (ganglion cells)
What kind of stimulus is needed for the PERG?
Phase reducing checkerboard
What can throw the test of the PERG
Accom or looking away
What damage is seen with multifocal ERG?
Damage to outer retina
What stimulus is used with mfERG?
Honeycomb pattern
What do the results of the mfERG look like?
Each hexagon of honeycomb will have an a and b wave showing that area’s response to the stimulus. If flatlined, means not sensitive to stimuli in that area
Why would you use the mfERG?
quantify progression/treatment
Quick list of clinical applications
Patency of choroid and retina
Locate damage
Differentiate rod or cone damage
What would you look for when trying to locate damage of the retina? What test would you use?
Use flash ERG. Allows you to see whole wave. Look at A wave. If bad, means photoreceptors doing badly. Look at B wave. If that’s bad then bipolar and muller cells are bad
How would you find the patency of the retina or choroid?
Do focal or full field ERG
How could you differentiate rod vs cone damage with the ERG?
Measure with different CFFs
Rods can’t see over 30Hz so if get signal, cones must be okay. Scotopic curve can be seen with entire a,b (c) wavelet. Photopic can use test that gives you sine wave looking function.
