Publication Date

2017-03-13

Availability

Open access

Embargo Period

2017-03-13

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Electrical and Computer Engineering (Engineering)

Date of Defense

2016-04-01

First Committee Member

Michael Renxun Wang

Second Committee Member

Manohar N. Murthi

Third Committee Member

Onur Tigli

Fourth Committee Member

Xiaodong Cai

Fifth Committee Member

Fabrice Manns

Abstract

Dry eye debilitates the patients physically, limit their ability to perform daily tasks, cause clinical depression, and compromise quality of life. Accurate diagnosis of the dry eye and the research on the pathological mechanism and treatment both depend largely on the available measurement techniques. The development of new measurement techniques helps better understanding of the disease and paves the way for accurate early diagnosis and better treatment. The purpose of this study was to develop additional tools in ophthalmic study for non-invasive high resolution tear film thickness evaluation and eye imaging. Optical coherence tomography (OCT) is a non-invasive imaging technology that has been widely used for ophthalmology imaging. It has also been used for tear film thickness measurement. But the axial resolution of a few microns is not sufficient because the whole tear film thickness is on a similar scale as the OCT resolution and the lipid layer is only tens of nanometers which is too thin to be visible by the OCT imaging. We introduced for the first time an optical reflectometer system for tear film thickness evaluation. The reflectometer system utilizes optical fibers to deliver illumination light to the tear film and collect the film reflectance data as a function of wavelength. To achieve near normal light incidence on the cornea for reflectance data acquisition, a fast galvanometer scanner is used for the best measurement beam alignment within 1 sec. Film thickness is determined by best fitting the spectral reflectance curve. The system's spectral reflectance acquisition time is 15 ms, fast enough for detecting film changes and studying film thinning dynamics. The time dependent reflectance data were saved to files and the curve fitting tear film thickness evaluation were subsequently performed. Tear film thickness and thinning process on a model eye and several human eyes have been successfully evaluated. Human tear film thicknesses thinning from 3.69 µm to 1.31 µm with lipid layer thickness variation in the range of 41 nm to 67 nm have been successful measured after one eye blink. We further report an integrated OCT and reflectometry system for ophthalmology imaging which can provide a 3D imaging of cornea and locate the position of tear film measurement on such 3D image. The dual-functional device provides a complementary high-resolution tear film evaluation by reflectometry and anterior segment imaging by OCT, offering a more comprehensive anterior segment examination. The imaging measurement capabilities have been demonstrated on a human eye as well as on a model eye. The tear film thickness measurement resolution is less than ±0.58% of film thickness yet the OCT anterior segment offers a depth resolution of 8.5 µm with a 43 nm bandwidth superluminescent light source at 840 nm center wavelength. To further provide the tear film thickness mapping, we improved the axial resolution of SD-OCT using a 100 nm bandwidth superluminescent light source and deconvolution technique with a selection of the suitable point spread function of the OCT system. Successful artificial tear thickness mapping on a model eye has been demonstrated.

Keywords

Tear Film; Reflectometry; Optical Coherence Tomography

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