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