part 14 Flashcards
ENG and VNG both assess what
occulomotor system and VOR
ENG and VNG both are trying to record
eye motion (nystagmus) and are getting graphs based on this
electronystagmography principle
corneoretinal potential
eyeball is electrical dipole
RPE metabolic activity that increases with light
explain eye as dipole
positive pole of cornea and back of eye negatively charged. difference maintained by CRP
when looking straight ahead what is the charge on the voltmeter
zero because equal distance to positive and negative charge
looking left what is charge on voltmeter if left is closer to negative
negative potential
looking right what is charge on voltmeter
postive voltage (closer to positive)
conjugate eye movement ENG
2 channels
- tracks movement of both eyes together
- horizontal and vertical tracker
negative deflection
eyes move toward negative electrode
positive deflection
eyes move toward positive electrode
when do we need discongjugate ENG
when eyes are not moving together and need separate eye measurements
deconjugate eye movement
4 channels measures each eye independently (2 horizontal and 2 vertical)
limitations of ENG
- eye movement not directly observed
-impacted by light - eye blink artifact
-insensitive to torsion
bells phenomenon (averting and aducction of eyes with eyes closed)
-deconjugate eye movement can skew data
scleral coil
gold standard electrode close to eyeball on cornea
VNG goggles how do they work
infared diodes (eyes cant see but camera can)
uses dichrotic glass mirrors letting in regular light but acting as mirror for infrared
software isolates pupils to track movement
Hough transform
alogrithm that detects pupil and center
purkinje image
first reflected image of light source on cornea- fixed reference point
pupil is darker than iris when
light is beside eye but does not clearly pass through pupil
pupil brighter than iris
red eye effect when light passes through iris
calibration for VNG and ENG
known eye to target distance is 4 ft
horizontal +/- 20 degrees vertical +/- 10 degrees
minimum of how many movements for each position (VNG/ENG)
8
the direction of the nystagmus quantifies what phase
fast phase
the amplitude of the nystagmus is quantified by what phase
slow phase
we calculate the digital representation for what phase
X/Y (rise over run) for slow phase bc we care about the magnitude of the impaired function, not the saccade
slow phase velocity is
rise over run or distance over time
nystagmus in horizontal channel which direction is positive motion
positive motion is right
in vertical channel when is positive deflection
on fast phase in upbeating
