DEVELOPMENT AND UTILIZATION OF NOVEL IMAGE PROCESSING TECHNIQUES TO CHARACTERIZE THE CHOROID IN ASIANS

Ph.DDOCTOR OF PHILOSOPH

Quantification and Predictors of OCT-Based Macular Curvature and Dome-Shaped Configuration: Results From the UK Biobank

PURPOSE. To investigate macular curvature, including the evaluation of potential associations and the dome-shaped macular configuration, given the increasing myopia prevalence and expected associated macular malformations. METHODS. The study included a total of 65, 440 subjects with a mean age (± SD) of 57.3 ± 8.11 years with spectral-domain optical coherence tomography (OCT) data from a unique contemporary resource for the study of health and disease that recruited more than half a million people in the United Kingdom (UK Biobank). A deep learning model was used to segment the retinal pigment epithelium. The macular curvature of the OCT scans was calculated by polynomial fit and evaluated. Further, associations with demographic, functional, ocular, and infancy factors were examined. RESULTS. The overall macular curvature values followed a Gaussian distribution with high inter-eye agreement. Although all of the investigated parameters, except maternal smoking, were associated with the curvature in a multilinear analysis, ethnicity and refractive error consistently revealed the most significant effect. The prevalence of a macular dome-shaped configuration was 4.8% overall, most commonly in Chinese subjects as well as hypermetropic eyes. An increasing frequency up to 22.0% was found toward high refractive error. Subretinal fluid was rarely found in these eyes. CONCLUSIONS. Macular curvature revealed associations with demographic, functional, ocular, and infancy factors, as well as increasing prevalence of a dome-shaped macular configuration in high refractive error including high myopia and hypermetropia. These findings imply different pathophysiologic processes that lead to macular development and might open new fields to future myopia and macula research

Optical coherence tomography angiography

Optical coherence tomography (OCT) was one of the biggest advances in ophthalmic imaging. Building on that platform, OCT angiography (OCTA) provides depth resolved images of blood flow in the retina and choroid with levels of detailed far exceeding that obtained with older forms of imaging. This new modality is challenging because of the need for new equipment and processing techniques, current limitations of imaging capability, and rapid advancements in both imaging and in our understanding of the imaging and applicable pathophysiology of the retina and choroid, and the requirement for understanding the origins of image artifacts. These factors lead to a steep learning curve, even for those with a working understanding dye-based ocular angiography. All for a method of imaging that is a little more than 10 years old. This review begins with a historical account of the development of OCTA, and the methods used in OCTA, including signal processing, image generation, and display techniques. This forms the basis to understand what OCTA images show as well as how image artifacts arise. The anatomy and imaging of specific vascular layers of the eye are reviewed. The integration of OCTA in multimodal imaging in the evaluation of retinal vascular occlusive diseases, diabetic retinopathy, uveitis, inherited diseases, age-related macular degeneration, and disorders of the optic nerve is presented. OCTA is an exciting, disruptive technology. Its use is rapidly expanding in clinical practice as well as for research into the pathophysiology of diseases of the posterior pole

SMART WEARABLES: ADVANCING MYOPIA RESEARCH THROUGH QUANTIFICATION OF THE VISUAL ENVIRONMENT

Myopia development has been attributed to eyeball elongation, but its driving force is not fully understood. Previous research suggests lack of time spent outdoors with exposure to high light levels or time spent on near-work as potential environmental risk factors. Although light levels are quantifiable with wearables, near-work relies solely on questionnaires for data collection and there remains a risk of subjective bias. Studies spanning decades identified that eye growth is optically guided. This proposal received further support from recent findings of larger changes in the thickness of the eye’s choroidal layer after short-term optical interventions compared with daily eye-length changes attributed to myopia. Most of these studies used a monocular optical appliance to manipulate potential myogenic factors, which may introduce confounders by disrupting the natural functionality of the visual system. This thesis reports on improvements in systems for characterising the visual dioptric space and its application to myopia studies. Understanding the driving forces of myopia will prevent related vision loss. Study I: An eye-tracker was developed and validated that incorporated time-of-flight (ToF) technology to obtain spatial information of the wearer’s field of view. By matching gaze data with point cloud data, the distance to the point of regard (DtPoR) is determined. Result: DtPoR can be measured continuously with clinically relevant accuracy to estimate near-work objectively. Study II: Near-work was measured with diary entries and compared with DtPoR estimations. Diversity of the dioptric landscape presented to the retina was assessed during near-work. Results: Objective and subjective measures of near-work were not found to highly correlate. Ecologically valid dioptric landscape during near-work decreases by up to -1.5 D towards the periphery of a 50˚ visual field. Study III: Choroid thickness changes were evaluated after exposure (approximately 30min) to a controlled, dioptrically diverse landscape with a global, sensitivity enhanced model. Result: No choroid thickness changes were found within the measuring field of approximately 45˚. Discussion The developed device could support future research to resolve disagreement between objective and subjective data of near-work and contribute to a better understanding of the ecological valid dioptric landscape. Proposed choroid layer thickness model might support short-term myopia-control research