Department of ORL-HNS Maastricht University Medical Centre The Netherlands

1. azM comparison video-oculography and electro-nystagmography using the search coil technique as a golden standard Department of ORL-HNS Maastricht University Medical Centre The Netherlands

2. 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)

3. electro-oculography /electro-nystagmography 50 Hz, drift, eye-blink + EMG artifacts, 2D, EO+EC

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

5. search coil technique (SCT): golden standard in clinic not accepted, 1000 Hz, 3D, EO + EC

6. 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)

7. 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

9. accuracy horizontal EOG VOG

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

11. detection of eye position EOG VOG 2D /3D 2D 2D sometimes 3D accuracy < 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°/s artefacts EMG,ECG, blinks blinks eyes open ok ok eyes closed ok not possible impact of light yes: CRP! no calibration necessary not necessary applicability 98% 80%

12. EOG versus VOG • are EOG and VOG appropriate to detect • saccade 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

13. frequency content saccades noise eog sct eog: high frequency noise bandwidth can be limited from 0 to about 25 Hz sample frequency of 50 Hz sufficient

14. 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 points • not enough to reconstruct peak velocity ? • literature: you need minimum 300 Hz • Nyquist signal reconstruction technique used • to calculate eye velocities (IEEE, 2007 )

15. validation Nyquist reconstruction algorithmwith SCT small saccade large saccade 0 50 100 150 200 0 100 200 300 400 ms 0 50 100 150 200 0 100 200 300 400 ms 1000 Hz 50 Hz 50 Hz reconstructed simulation using SCT 1000 Hz vs 50 Hz

16. simulation using SCT 1000 Hz vs 50 Hz

17. application for VOG of Nyquist reconstruction algorithm small large 0 200 400 600 800 0 100 200 300 400 500 ms 0 200 400 600 800 0 100 200 300 400 500 ms 50 Hz 50 Hz reconstructed simulation using SCT 1000 Hz vs 50 Hz

18. application for VOG of Nyquist reconstruction algorithm simulation using SCT 1000 Hz vs 50 Hz NB: peak velocities VOG even higher than peak velocities SCT ! artifact ?

19. is EOG appropriate to detect saccade peak velocities and latencies ? OS OD ODS OS OD leftwards rightwards - 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?

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

21. visual check of VOG images of the eye with search coil: search coil slips over the eye

22. 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)

23. azM • 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