In-vitro measurement of Intra- Ocular Pressure Alex Luce Undergraduate 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 10/28/2015Undergraduate Research Symposium - Alex Luce 2

Intraocular Pressure (IOP) The major risk factor for glaucoma Normal eye pressure : mm Hg 10X increased risk to develop glaucoma: >23mm Hg Measurement of the intraocular pressure (IOP) with an applanation tonometer 10/28/20153Undergraduate Research Symposium - Alex Luce

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: 10/28/20154Undergraduate Research Symposium - Alex Luce

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. F 1 (x) F 2 (x) 10/28/20155Undergraduate Research Symposium - Alex Luce

Force application Applied Force F 10/28/20156Undergraduate Research Symposium - Alex Luce

Force application 10/28/20157Undergraduate Research Symposium - Alex Luce

Force measurement Bending-beam load cell deflection of cantilever induces strain 10/28/2015Undergraduate Research Symposium - Alex Luce 8 Strain Gage Deformation of metal foil causes change in electrical resistance

Block Diagram of Experiment 10/28/2015Undergraduate Research Symposium - Alex Luce 9

Experimental setup 10/28/2015Undergraduate Research Symposium - Alex Luce 10

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10/28/201512Undergraduate Research Symposium - Alex Luce Force sensor Measure F Micrometer Measure x Syringe Adjust IOP

Force Sensor Calibration  Weights of known value measured with each force sensor  Voltage output measured  Standard deviation 0.3% of measured force 10/28/201513Undergraduate Research Symposium - Alex Luce

Experimental procedure  Adjust IOP: mmHG  FS1: Increment micrometer x - apply force F1 to eyeball  FS2: measure force F2 F1 F2 Pressure adjustment Applied force 10/28/201514Undergraduate Research Symposium - Alex Luce Disp. X

Experimental Results Increased Pressure Increased risk of glaucoma 10/28/201515Undergraduate Research Symposium - Alex Luce

10/28/2015Undergraduate Research Symposium - Alex Luce 16 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” 10/28/201518Undergraduate Research Symposium - Alex Luce

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 10/28/2015Undergraduate Research Symposium - Alex Luce 19

Acknowledgements  Dr. Eniko Enikov, Dr. Gholam Peyman, Vasco Polyzoev, Balint Magyar, Ed White  Advanced Microsystems Lab  Funding from NSF Grant CBET /28/201520Undergraduate Research Symposium - Alex Luce