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Intraocular Pressure Optical Sensor Reader

Spring 2018 MAE 156B Sponsored Senior Design Project

University of California, San Diego

Link to executive summary 

Project Background

This project is sponsored by Professor Frank Talke's Mechanics and Tribology Lab at the Center for Memory and Recording Research (CMRR) at the UCSD main campus. Our sponsor has developed an interferometry based intraocular pressure (IOP) sensor that can be used to diagnose glaucoma, a degenerative eye disease. This interferometry based IOP sensor correlates the fringe patterns, which result from the interference of light waves on the embedded IOP sensor, with pressure in the eye. With this reading, patients at risk of glaucoma can monitor their eye pressure health at greater ease and seek timely treatment.

Objective

The purpose of this work is to develop a hand-held, compact, and portable reader which can easily be used by the patient to capture the fringe patterns on the implanted IOP sensor. A smartphone application will be used in conjunction with the hand-held reader to assist the patient in obtaining a clear and appropriate image of the IOP sensor and send that directly over to a health professional.  

Final Design

Optics: 

The image on the left is the fully functional optical reader in action. It is able to capture the fringe patterns on a static sensor. The diagram on the right is an overview of the optical design of the project. It features 3 aspheric lenses, a mirror, a condenser lens, and a red LED light as our light output. 

Smartphone application:

The first figure above is the home screen of the smartphone application for streamlining the process of obtaining eye pressure readings. The application has three main functions: take a photo, select an image to perform image processing and pressure calculations, and viewing a log of previous pressure measurements. After selecting an image, the app runs the user through image processing and eventually leads to a value for the eye pressure reading. 

Results

Experiments were conducted to verify the performance of the IOP reader. The range of pressures tested on the optical system are 0 to 30 mmHg in increments of 5 mmHg. The figure below shows the image processing (cropping and deformation plots) of an ambient IOP sensor with 0 mmHg of applied pressure. Overall, the IOP reader was able to achieve clear images of the IOP sensor with an absolute error of 8.28% with a standard deviation of 25.04%. From what was observed, one major drawback is the field of view of the system. In experimentation, this proved to be true, as any slight movement of the IOP reader placed the IOP sensor out of focus. Hence, the IOP reader needed to be fixed in place for the desired performance.

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