In-vitro measurement of Intra- Ocular Pressure Alex Luce Undergraduate Research Symposium 2008.
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Transcript of In-vitro measurement of Intra- Ocular Pressure Alex Luce Undergraduate Research Symposium 2008.
In-vitro measurement of Intra-Ocular Pressure
Alex LuceUndergraduate Research Symposium 2008
Motivation: Treat Glaucoma
Glaucoma: a degenerative
disease of the eye
•Affects 3 million Americans
•Leading cause of adult
blindness in the world
•No available cure
•Entirely preventable if
caught early!
Normal range of vision
Advanced vision loss due to glaucoma
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Intraocular Pressure (IOP)The major risk factor for glaucoma
Normal eye pressure : 10-21 mm Hg
10X increased risk to develop glaucoma: >23mm Hg
Measurement of the intraocular pressure (IOP) with an applanation tonometer
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Methods to Measure IOP
Indirect Methods:•Applanation Tonometry (ex. Goldman Applanation Tonometry)
•MacKay-Marg tonometry
•Digital Palpation Tonometry
Measurement of IOP with Dynamic Contour Tonometer. Measurements must be performed in clinical setting.
Problems:•Diurnal pressure variation (24 hr cycle)•Laser eye surgery•Requires anesthesia •Potential for infection•Cannot be completed at home
Photo credit: http://en.wikipedia.org/wiki/Image:PASCAL_tonometer.jpg
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Experiment Goal
Utilize concept of digital palpation tonometry for experimental IOP measurements
Determine required sensor specifications
Digital palpation tonometry: fingertips push on eye- ‘feel’ pressure Measure F vs X vs IOP
Disp.F1(x) F2(x)
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Force application
Applied
Force F
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Force application
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Force measurement
Bending-beam load cell•deflection of cantilever induces strain
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Strain Gage•Deformation of metal foil causes change in electrical resistance
Block Diagram of Experiment
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Experimental setup
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Force sensor•Measure F
Micrometer•Measure x
Syringe•Adjust IOP
Force Sensor Calibration
C alibration C urve F S 2
0
0.1
0.2
0.3
0.4
0.5
0 5 10 15
Applied We ig ht (g )
Mea
sure
d v
olt
age
(Vo
lt)
Weights of known value measured with each force sensor
Voltage output measured
Standard deviation 0.3% of measured force
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Experimental procedure Adjust IOP: 10-35
mmHG FS1: Increment
micrometer x - apply force F1 to eyeball
FS2: measure force F2
F1 F2
Pressure adjustment
Applied force
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Disp. X
Experimental Results
•Increased Pressure•Increased risk of glaucoma
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Disp. (mm)
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Conclusions Digital palpation tonometry: a viable IOP
measurement technique
To screen for glaucoma, required sensor resolution is.: F ≤ 0.5N, x ≤ 0.5mm.
Force measurements must be done below ~2.5 N, to avoid errors introduced by motion of eye in model “socket”
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Future Work Compare experimental
results of experiment to Finite Element simulation
Develop motorized experiment to mimic human palpation exam institute
Explore means to measure IOP independently of displacement
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Acknowledgements Dr. Eniko Enikov, Dr. Gholam Peyman, Vasco
Polyzoev, Balint Magyar, Ed White Advanced Microsystems Lab Funding from NSF Grant CBET-0603198
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