Measurement of intraocular pressure (IOP) is an important diagnostic tool in clinical ophthalmology. Elevated IOP is the leading cause of Glaucoma, a disease leading to damage of the optic nerve and subsequently, to blindness. Currently IOP is measured via the Goldman?s applanation tonometer, a mechanical device that measures the force required to flatten the cornea to a prescribed contact area. Palpation (digital) tonometry measures the intraocular pressure through the eyelid and therefore, does not require anesthesia and instrument sterilization. The objective of this proposal is to demonstrate a wearable tactile sensor that can be used for frequent measurements of IOP at home. The proposed tissue modeling and analysis will generate a 3D stiffness map of the eye and improve our understanding of the mechanical properties of the eye and its tissues. Societal benefits of the proposed research include reduced need for hospital visits and better management of episodes of elevated IOP and glaucoma. Further potential applications include prostate and breast cancer screening.

The project will provide training opportunities for graduate and undergraduate students. An innovative application of LEGO Mindstorms educational robotics to the task of testing of the proposed sensors will provide participation opportunities for undergraduate students and STEM teachers.

Project Report

Tactile sensors are used to measure the contact force (or pressure) during touch. Recently, tactile sensors have been explored as medical diagnostic devices due to their ability to measure stiffness and elastic?related properties of soft materials such as human tissue. Potential medical applications of tactile sensors include detection of breast and prostate tumors, or measurement if eye pressure. The measurement of intraocular pressure (IOP) through tactile sensing is a technique known as (digital) palpation tonometry. Digital palpation tonometry is performed by lightly pressing the fingertips of both index fingers onto the upper part of the eye through the eyelid. The objective of this project is to demonstrate that tactile sensors can be used to measure IOP, which could lead to the development of a home eye tonometer. Further goals of the project are to understand the biomechanical response of soft tissues and organs containing incompressible fluids. In addition to examining different sensing modalities, this project examined the factors influencing the accuracy of the eye pressure estimation and developed methodology for sensor calibration. Intellectual Merit: To date, measurement of the intraocular pressure is only possible under local anesthesia, using the cornea of the eye. Less direct measurements have had limited accuracy and, therefore, limited diagnostic value. This project developed a novel system capable of extracting eye pressure and other tissue response parameters via simultaneous measurement of contact forces from multiple probes applied to the sclera or the eye lid. It further demonstrate that accurate pressure sensing (within +/- 2 mmHg) requires controlled rate of application of the tactile probes. The repeatability of the technique is also affected by the orientation of the probes.An alignment mask with integrated sensors and advancement mechanism was designed to address these challenges. Broader Impact: Elevated intraocular pressure (IOP) is universally accepted as one of the most important risk factors contributing to the development of glaucoma and the subsequent progression to blindness. Adults over the age of 40 develop this disease and are sometimes unknowingly going blind. In the US alone, more than 8.7 million office visits are made each year for the diagnosis or treatment of glaucoma. Due to natural variation of eye pressure, it may be possible to miss an episode of elevated eye pressure. Therefore, frequent measurement of the IOP throughout the day would allow for significant improvement in the treatment outcome and early diagnosis of glaucoma. This project developed the first prototype of such system which could lead to the development of the first accurate home tonometer operating on the principle of tactile tonometery. The commercial and economic impact of this technology, in US alone, is estimated to be $1B. Similar market opportunities exist in the rest of the developed world.

Project Start
Project End
Budget Start
2009-08-01
Budget End
2013-07-31
Support Year
Fiscal Year
2008
Total Cost
$269,815
Indirect Cost
Name
University of Arizona
Department
Type
DUNS #
City
Tucson
State
AZ
Country
United States
Zip Code
85721