Morphometric Analysis of Ophthalmic Optical Coherence Tomography Images

Optical coherence tomography (OCT) has become a standard in the field of ophthalmology by providing in-vivo, high-resolution, cross-sectional images of the inner structures of the eye. This dissertation outlines the construction and application of a computational pipeline for morphometric analysis of 3D retinal and peripapillary OCT images with the goal of extracting clinically meaningful information based on shape features. The images were acquired by a prototype 1060-nm swept-source OCT system and processed to correct motion and enhance the image quality. Next, anatomical features were segmented, in particular the retinal layers and structures in the optic nerve head (ONH) and laminar regions, such as the Bruch’s membrane opening (BMO) and anterior laminar boundaries. A graph-cut based, robust 3D algorithm was implemented for automated segmentation of the retinal layers. The shape of the segmented structures was measured by quantitative parameters, such as 3D thickness of the layers and dimension of the BMO. A special focus was given to establishing anatomical correspondence across multiple OCT images, from longitudinal or cross-sectional data, via registration / atlas methods. In the first approach, retinal surfaces from two OCT images were registered by a mathematical current-based deformation followed by spherical demons registration. In the second approach, retinal surfaces and corresponding signal values (ex. layer thickness) from several OCT images were jointly varied to generate a group mean template. The geometrical and signal variability among the surfaces were measured by their distances to the template serving as the common atlas. In clinical application of the pipeline, peripapillary OCT volumes of 52 myopic eyes from both normal and glaucomatous subjects were studied. Retinal layer thicknesses, shape of the BMO, bowing of Bruch’s membrane, shape of the anterior scleral canal, anterior laminar insertion, and anterior laminar surface were measured and statistically analyzed. Significant differences were observed between the normal and glaucomatous groups and demonstrated in detail the nature of the structural deformation in the glaucomatous eyes. Additionally, the results correlated the degree of myopia to several structural changes in the region, suggesting possible clues to the mechanism behind the high glaucoma susceptibility associated with advanced myopia.