Mag Eye Tracking Using Planar Txr by v.k.charUSREE S7 EC

8/8/2019 Mag Eye Tracking Using Planar Txr by v.k.charUSREE S7 EC

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MAGNETIC EYE TRACKING

USING PLANAR TRANSMITTER

Charusree.V.KNo:29

S7 EC A


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INTRODUCTION

Allows diagnosis of neurologic,ophthalmologic

& vestibular disorders.

Conventional ssc s/m employs cubical txr. Thin ,flat txr.

Convenient in installation,operation &

maintanance. Planar txr increases mobility of ssc s/m,

simplifies accomodation in limited clinical

space,enables bedside testing,no discomfortetc.


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EYE TRACKING

Eye movement,most frequent of all human

movements.

Eye tracking is the process of measuring pointof gaze or moton of eye relative to head.

Eye tracker measures eye position & eye

movements. Used in research on visual

s/m,psychology,cognitive linguistic & in

product design.


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TECHNIQUES

Electro oculography

Infrared oculography

Image based results

Magnetic eye tracking


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ELECTRO OCULOGRAPHY

Measures resting potential of retina.

Potential difference of pairs of electrodes are

measured.

Eye acts as a dipole(working principle ofelectrooculography)

Electrooculogram and tracing displayed by a pen record.


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INFRA RED OCULOGRAPHY

Light source is directed to eye.

Measured the amount of light reflected back.

Infra red not influenced by other light.

Spatial resolution 0.1o

Temporal resoluton 1ms.

Drawback is 'blink' of eyes.


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IMAGE BASED RESULTS

Automatically extracting eye position fromimages of the eye.

Measures vertical & horizontal eye movement.

Temporal resolution lower than IR method.


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MAGNETIC EYE RACKER

Sensor & txr station.

More accuracy than optical camera.

It gives 3D orientaton.

Main drawback is that,it is wired.


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MAGNETIC EYE TRACKER

Using Scleral Search Coils:

Uses magnetic induction to track 'gaze' Eye position is recorded depending on voltage

generated in coil by exposure to alternatingmagnetic field.

Medical-grade silicon rubber suction ring

Shape to adhere to the limbus.

Disadvantages are invasive nature of coil,limited

lifetime etc.


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Scleral search coil


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Using Cubical Txr:

Large cubic txr.

Wide area of txng coil-high magnetic

field,highS

NR & tracking precision. High tracking speed.

Bulky & awkward. Difficult to install,operate & maintain.

Visual distraction.


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Using Planar Txr:

Coplanar array of txng coils,keeps txr thin. Minimum possible no.of txng coils.

8 coplanar coils,provide best tracking

precision for each txng coil.

Each coil is excited at its own frequency.

It excites coils continuously &

simultaneously.


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Construction & Working

Txng coil:

Coil is conneced via Ci,to half bridge excitation ckt.

Half bridge excites txng coil.

BS170 MOSFET translates 5v to 12v pulses.

20 ohm resistor limits gate current. 0.1 ohm resistor to measure excitaton current.

Ci chosen such that resonant freq. matchesexcitation freq.


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Half bridge ckt for excitation of txng coil


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Rxng coil:

Radius ofSSC is 9mm & no.of turns is 7(eyeposition)

Custom made coil of 5mm radius 200 turns (headposition)

Head coil mounted on mouth piece.


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Testing applicability:

Compared b/n Bilateral meniere affected &

normal prson.

Calculate Vestibular Ocular Reflex(VOR) VOR gain of healthy man would be greater

than affected one.

Ideally VOR would be 1.


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a ) Ma g n e t ic t r a c k in g u s in g c u b ic t r a n s m i t t e r , b ) Us in g p l a n a r

t r a n s m i t t e r

a) VOR gain o f he althy o ne , b)of a no n he althy perso n


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APPLICATIONS

Cognitive study

Commercial aplictios (web,

add.,design,marketing, automotive etc.) Communication s/m for disabled.

Improved image & video communication.


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CONCLUSION

Thin flat planar txr,instead of bulky

conventional cubic txr.

Increased speed & precision. Diagnosis of vestibular disorders.

Can improve tracking precision by

increasing radius of txng coil. & increasedexcitation freq.


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Documents

Mag Eye Tracking Using Planar Txr by v.k.charUSREE S7 EC