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

04/20/23 Undergraduate Research Symposium - Alex Luce

2

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

04/20/23 3Undergraduate 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: http://en.wikipedia.org/wiki/Image:PASCAL_tonometer.jpg

04/20/23 4Undergraduate 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.F1(x) F2(x)

04/20/23 5Undergraduate Research Symposium - Alex Luce

Force application

Applied

Force F

04/20/23 6Undergraduate Research Symposium - Alex Luce

Force application

04/20/23 7Undergraduate Research Symposium - Alex Luce

Force measurement

Bending-beam load cell•deflection of cantilever induces strain

04/20/23 Undergraduate Research Symposium - Alex Luce

8

Strain Gage•Deformation of metal foil causes change in electrical resistance

Block Diagram of Experiment

04/20/23 Undergraduate Research Symposium - Alex Luce

9

Experimental setup

04/20/23 Undergraduate Research Symposium - Alex Luce

10

04/20/23 11Undergraduate Research Symposium - Alex Luce

04/20/23 12Undergraduate Research Symposium - Alex Luce

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

04/20/23 13Undergraduate Research Symposium - Alex Luce

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

04/20/23 14Undergraduate Research Symposium - Alex Luce

Disp. X

Experimental Results

•Increased Pressure•Increased risk of glaucoma

04/20/23 15Undergraduate Research Symposium - Alex Luce

04/20/23 Undergraduate Research Symposium - Alex Luce

16

Disp. (mm)

04/20/23 17Undergraduate Research Symposium - Alex Luce

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”

04/20/23 18Undergraduate 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

04/20/23 Undergraduate 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-0603198

04/20/23 20Undergraduate Research Symposium - Alex Luce