Dynamic characterization of ocular surface with thermography and macroscopic imaging ellipsometry

Thesis (Ph. D.)--University of Rochester. Institute of Optics, 2017.Visual acuity and comfort is strongly influenced by the homogeneity and integrity of the ocular tear film. The tear film is established with each blink and after a period of time it will break, leading to a loss of visual acuity and comfort to stimulate another blink. Chronic disorders of tear film lead to a prevalent problem of dry eye syndrome. The goal of my research is to develop objective and quantitative tools for dry eye syndrome diagnosis. The tear film health is directly associated with the environmental conditions such as temperature, humidity and air flow rate. Using thermography, I investigated the relation of the dynamic ocular surface temperature with the environment, and analyzed normal and dry eye subjects and different subgroups of dry eye subjects. I developed a thermal impulse perturbation (TIP) model to describe the fast heating of the ocular surface during each blink by the eyelids and redistributed tears. I studied the bioheat transfer mechanisms of the ocular surface cooling after a blink and experimentally measured the evaporation and convection coefficients in both normal and stressed clinical environments. Furthermore, I developed a second generation (2G) tearscope, using macroscopic imaging ellipsometry (MIE) that can simultaneously measure the thickness and refractive index of a film covering a flat or curved substrate. MIE was tested and validated with bare BK7 and SF11 substrates, MgF2 anti-reflection coated and Al2O3 coated BK7 substrates with curvatures approximating the human cornea. I also tested the flat witness samples on microscope slides and Si wafers, from the same coating runs with the curved coated samples. The final results were compared with the flat witness sample results from the profilometer, the J.A. Woollam Alpha SE ellipsometer, and the Filmetrics reflectometer. The thicknesses accuracy of the MIE is ±15 nm and the refractive index accuracy is ±0.05. The relaxed sample alignment tolerance is ±10 mm laterally in the focal plane, and ±2.5 mm axially. With further development, MIE has the potential to provide simultaneous measurements of lipid layer thicknesses and refractive indices, which may provide better clinical diagnosis of dry eye syndrome