UBC Theses and Dissertations
Corneal visualization and characterization for applications in ophthalmology using optical imaging Lai, Tom Yu Chia
Multiphoton microscopy (MPM) and optical coherence tomography (OCT) are two modalities suitable for imaging corneas. MPM is a nonlinear optical imaging technique that has sub-micron spatial resolution, deep penetration, and excellent optical-sectioning capability. It can detect two contrasts simultaneously: two-photon excited fluorescence (TPEF) and second harmonic generation (SHG). TPEF and SHG are used to visualize cells and collagen fibers, respectively. On the other hand, OCT is based on the detection of single-backscattered light using interferometry principles. Generally, it has micrometer-resolution and up to a few millimeters of imaging-depth. Combining MPM and OCT for corneal imaging is intuitive in the current study as the complementary information obtained from cornea helps us to understand the morphological and physiological status of the cornea. Furthermore, the MPM and OCT images can be used to quantitatively characterize the thicknesses and refractive index (RI) of the major corneal layers. The visualization of the corneal morphology is important in ophthalmology. It can be used to: study the effects of contact lens wear and topical medications; diagnose corneal diseases such as infectious keratitis; and observe corneal ulcers, and keratoconous. In addition, the ability to quantitatively characterize the corneal thickness and RI is valuable for many ophthalmologic applications. These two parameters are useful for laser refractive surgeries, and the diagnosis of corneal degeneration, and endothelial dysfunction. They are also linked to other important parameters such as corneal hydration and intraocular pressure. In this thesis, the capabilities of a combined MPM and OCT system for corneal imaging are demonstrated. Firstly, it is used to simultaneously visualize and compare the morphology, and to characterize the thicknesses and the RI of five different species’ corneas. In order to visualize the thicker tissues, the OCT modality is altered in two ways: a prism-based hardware dispersion balancing unit is added to minimize the dispersion mismatch in OCT; and an additional OCT configuration of objective lens and spectrometer setup was introduced. Secondly, the combined system is used to identify an induced parasitic infection in human corneas. The study serves as an important step forward to bring the combined MPM and OCT technology to clinical settings.
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