department of orl-hns maastricht university medical centre the netherlands

Department of ORL-HNSMaastricht University Medical Centre

The Netherlands

comparison video-oculography and electro-nystagmography using the search coil technique as a golden standard

azM

EOG versus VOG

which eye movement recording technique is optimal for the clinical setting ?

- clinical relevant eye movement types: spontaneous, fixation, pursuit, saccades, nystagmus

- requirements: easy and comfortable application accuracy, precision, spatial resolution (Δ°), time resolution (Δt)

electro-oculography /electro-nystagmography50 Hz, drift, eye-blink + EMG artifacts, 2D, EO+EC

video-oculography (VOG) / video-nystagmography (VNG)50 Hz, 3D but limited range, only EO

search coil technique (SCT): golden standardin clinic not accepted, 1000 Hz, 3D, EO + EC

EOG versus VOG

which eye movement recording technique is optimal for the clinical setting ?

- clinical relevant eye movement types:spontaneous, fixation, pursuit, saccades, nystagmus

- requirements: easy and comfortable application accuracy, precision, spatial resolution (Δ°), time resolution (Δt)

EOG versus VOG

which eye movement recording technique is optimal for the clinical setting ?

method:

- simultaneous recording of eye movements with EOG, VOG and SCT- exclusion of interference between the techniques- 6 healthy subjects- comparison of accuracy / drift / artefacts- comparison of time resolution

accuracy horizontal

EOG VOG

accuracy vertical

EOG VOG

- vertical eye movements can be analysed with EOG !- limited range EOG and VOG: 20°

detection of eye position

EOG VOG2D /3D 2D 2D sometimes 3Daccuracy < 3° < 0.5°precision (reproducibility) < 1° < 0.5°spatial resolution < 0.5 ° < 0.2 °field of view H x V unlimited 40 x 40°range H x V 80 x 60° 40 x (10-40)°linearity horizontal 25° 25°linearity vertical 20° 20°drift 0 – 5 °/s 0°/sartefacts EMG,ECG, blinks blinkseyes open ok okeyes closed ok not possibleimpact of light yes: CRP! nocalibration necessary not necessaryapplicability 98% 80%

EOG versus VOG

are EOG and VOG appropriate to detectsaccade latencies and peak velocities (time resolution) ?

method: - simultaneous recording of eye movements with EOG, VOG and SCT- exclusion of interference between the techniques- 6 healthy subjects- comparison of accuracy / drift / artefacts- comparison of time resolution:

* analysis of frequency compound of eye movements (SCT) in relation to the limited frequency range of EOG (noise) and VOG (25-50 Hz sample frequency)

* development of special signal analysis techniques for VOG

frequency content saccades

sct eog

eog: high frequency noise bandwidth can be limited from 0 to about 25 Hz

sample frequency of 50 Hz sufficient

noise

0 50 ms

VOG

which eye movement recording technique is optimal for the clinical setting ?

are EOG and is VOG appropriate to detect saccade peak velocities

- problem with VOG: 50 Hz ~ 20 ms saccade lasts only 50 ms: 2 data pointsnot enough to reconstruct peak velocity ?literature: you need minimum 300 Hz

Nyquist signal reconstruction technique used

to calculate eye velocities (IEEE, 2007 )

simulation using SCT 1000 Hz vs 50 Hz

0 50 100 150 200 0 100 200 300 400 ms

0 50 100 150 200 0 100 200 300 400 ms

validation Nyquist reconstruction algorithm with SCT

1000 Hz 50 Hz 50 Hz reconstructed

smallsaccade

largesaccade

simulation using SCT 1000 Hz vs 50 Hz

simulation using SCT 1000 Hz vs 50 Hz

0 200 400 600 800 0 100 200 300 400 500 ms

application for VOG of Nyquist reconstruction algorithm

50 Hz 50 Hz reconstructed

small large

0 200 400 600 800 0 100 200 300 400 500 ms

simulation using SCT 1000 Hz vs 50 Hz

application for VOG of Nyquist reconstruction algorithm

NB: peak velocities VOG even higher than peak velocities SCT ! artifact ?

- asymmetry EOG in case of monocular detection: artifact - binocular detection (100 Hz LPF, 1000 Hz SF): good estimates of latencies and peak velocities

NB: peak velocities EOG even higher than peak velocities SCT ! artifact?

leftwards rightwards

OD

ODOS

OS

ODS

is EOG appropriate to detect saccade peak velocities and latencies ?

comparison data SCT+VOG+EOG versus VOG+EOG:

- eye velocities detected with EOG and VOG are slower with COIL on the eye than without COIL on the eye

- search coil slows down eye velocities

peak velocities of both EOG and VOG are higher than peak velocities SCT !

visual check of VOG images of the eye with search coil:

search coil slips over the eye

- SCT- no perfect golden standard (coil slips and slows down the eye)

- VOG - optimal for BPPV - OD and OS saccades can be analysed with a 50 Hz system- but field of view and range are limited

- often detection fails (> 20% !) and 3D is often unreliable- EOG

- robust clinical method for binocular recordings- eo / ec, unlimited field of view, large range of detection H+V - only binocular saccades can be analysed reliable- but drift and noise can hamper a good detection (training)

EOG versus VOG which technique

is optimal for the clinical setting ?

• EOG is the first choice to deal with all patients

• VOG is very useful for BPPV and complex patients

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