Applications of optical coherence tomography imaging in the assessment of glaucoma

Summary. Glaucoma is a progressive optic neuropathy characterized by the loss of retinal ganglion cells resulting in constriction of visual field and loss of vision as the disease progresses. Since structural damage in glaucoma occurs well before any detectable loss in visual function, clinical examination of the optic nerve head and its nerve fiber layer is crucial in establishing the diagnosis, monitoring the progression and initiating treatment before irreversible damage takes place. The present research project is composed of 7 coherent studies (sections 3.1 to 3.7), aiming to investigate the clinical applications of optical coherence tomography (OCT), an advanced imaging device for detailed examination of optic nerve head and nerve fiber layer, in the assessment of glaucoma.; Sections 3.1 to 3.3 were designed to identify the most sensitive and specific diagnostic marker(s) for glaucoma detection. Peripapillary retinal nerve fiber layer (RNFL), macular thickness, optic nerve head parameters measured with different reference planes, and a novel anatomic marker - macular nerve fiber layer were investigated. The averaged peripapillary RNFL thickness measured with a high resolution scan (512 scan point) was found to have the best discriminating power for detection of glaucoma. It also has the strongest correlation with visual function. To examine if utilization of the complete data profile of peripapillary RNFL could further improve diagnostic sensitivity, a novel approach with the use of neural network trained to recognize RNFL pattern was studied in section 3.4. It was concluded that neural network analysis could enhance the diagnostic performance for glaucoma detection.; In section 3.5, RNFL measurement by OCT was cross-validated by another nerve fiber analyzer, scanning laser polarimetry (SLP). While both OCT and SLP demonstrated comparable diagnostic performance for glaucoma detection and high correlation in the respective RNFL measurements, OCT was found to provide a closer estimation of RNFL thickness with reference to the reported histological measurements. In section 3.6, the structural-functional relationship between RNFL thickness and visual sensitivity was evaluated and compared between OCT and SLP. The relationships were found to be dependent on the choice of the perimetry scale, the type of RNFL measuring devices and the characteristics of the studied subjects. It was concluded that regression analysis of the structural-functional profile could provide important information in the assessment of the trend and pattern of glaucoma progression.; Although the current OCT imaging system was designed to examine the retinal structures, a novel application in imaging the anterior chamber angle was studied in section 3.7. OCT was demonstrated to be clinically useful for visualization of the different patterns of angle configurations in different forms of angle closure glaucoma.; In summary, optical coherence tomography was shown to be useful in the diagnosis of glaucoma and in the evaluation of the trend and pattern of disease progression.; Objectives. The research project was designed to investigate the applications of optical coherence tomography in the assessment of glaucoma. The goals are to identify sensitive and specific anatomic markers, and analytical method for detection of glaucomatous changes, to evaluate the intricate structural-functional relationships in glaucoma with regression analysis and to assess the potential application of optical coherence tomography imaging system in visualization of the anterior chamber angle with a view to obtain OCT data to help understanding the pathophysiology of different forms of angle-closure glaucoma.