part 14

Question 1

ENG and VNG both assess what

Answer 1

occulomotor system and VOR

Question 2

ENG and VNG both are trying to record

Answer 2

eye motion (nystagmus) and are getting graphs based on this

Question 3

electronystagmography principle

Answer 3

corneoretinal potential
eyeball is electrical dipole
RPE metabolic activity that increases with light

Question 4

explain eye as dipole

Answer 4

positive pole of cornea and back of eye negatively charged. difference maintained by CRP

Question 5

when looking straight ahead what is the charge on the voltmeter

Answer 5

zero because equal distance to positive and negative charge

Question 6

looking left what is charge on voltmeter if left is closer to negative

Answer 6

negative potential

Question 7

looking right what is charge on voltmeter

Answer 7

postive voltage (closer to positive)

Question 8

conjugate eye movement ENG

Answer 8

2 channels
- tracks movement of both eyes together
- horizontal and vertical tracker

Question 9

negative deflection

Answer 9

eyes move toward negative electrode

Question 10

positive deflection

Answer 10

eyes move toward positive electrode

Question 11

when do we need discongjugate ENG

Answer 11

when eyes are not moving together and need separate eye measurements

Question 12

deconjugate eye movement

Answer 12

4 channels measures each eye independently (2 horizontal and 2 vertical)

Question 13

limitations of ENG

Answer 13

• 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

Question 14

scleral coil

Answer 14

gold standard electrode close to eyeball on cornea

Question 15

VNG goggles how do they work

Answer 15

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

Question 16

Hough transform

Answer 16

alogrithm that detects pupil and center

Question 17

purkinje image

Answer 17

first reflected image of light source on cornea- fixed reference point

Question 18

pupil is darker than iris when

Answer 18

light is beside eye but does not clearly pass through pupil

Question 19

pupil brighter than iris

Answer 19

red eye effect when light passes through iris

Question 20

calibration for VNG and ENG

Answer 20

known eye to target distance is 4 ft
horizontal +/- 20 degrees vertical +/- 10 degrees

Question 21

minimum of how many movements for each position (VNG/ENG)

Answer 21

8

Question 22

the direction of the nystagmus quantifies what phase

Answer 22

fast phase

Question 23

the amplitude of the nystagmus is quantified by what phase

Answer 23

slow phase

Question 24

we calculate the digital representation for what phase

Answer 24

X/Y (rise over run) for slow phase bc we care about the magnitude of the impaired function, not the saccade

Question 25

slow phase velocity is

Answer 25

rise over run or distance over time

Question 26

nystagmus in horizontal channel which direction is positive motion

Answer 26

positive motion is right

Question 27

in vertical channel when is positive deflection

Answer 27

on fast phase in upbeating