Typescript (photocopy). / Digitized by Kansas Correctional Industries

No / The purpose of the research was to describe a software package (Discus) for investigating clinicians' subjective assessment of optic disc damage [diagnostic accuracy in detecting visual field (VF) damage, decision criteria, and agreement with a panel of experts] and to provide reference data from a group of expert observers. Optic disc images were selected from patients with manifest or suspected glaucoma or ocular hypertension who attended the Manchester Royal Eye Hospital. Eighty images came from eyes without evidence of VF loss in at least four consecutive tests (VF negatives), and 20 images from eyes with repeatable VF loss (VF positives). Software was written to display these images in randomized order, for up to 60 s. Expert observers (n = 12) rated optic disc damage on a 5-point scale (definitely healthy, probably healthy, not sure, probably damaged, and definitely damaged). Optic disc damage as determined by the expert observers predicted VF loss with less than perfect accuracy (mean area under receiver-operating characteristic curve, 0.78; range, 0.72 to 0.85). When the responses were combined across the panel of experts, the area under receiver-operating characteristic curve reached 0.87, corresponding to a sensitivity of ∼60% at 90% specificity. Although the observers' performances were similar, there were large differences between the criteria they adopted (p < 0.001), even though all observers had been given identical instructions. Discus provides a simple and rapid means for assessing important aspects of optic disc interpretation. The data from the panel of expert observers provide a reference against which students, trainees, and clinicians may compare themselves. The program and the analyses described in this article are freely accessible from http://www.discusproject.blogspot.com/.

Ophthalmic diseases such as glaucoma are associated with progressive changes in the structure of the optic disc (OD) and parapapillary atrophy (PPA). These structural changes may therefore have relevance to other systemic diseases. The size and location of OD and PPA can be used as registration landmarks for monitoring changes in features of the fundus of the eye. Retinal vessel evaluation, for example, can be used as a biomarker for the effects of multiple systemic diseases, or co-morbidities. This thesis presents the first computer-aided measuring tool that detects and quantifies the progression of PPA automatically on a 2D retinal fundus image in the presence of image noise. An automated segmentation system is described that can detect features of the optic nerve. Three novel approaches are explored that extract the PPA and OD region approximately from a 2D fundus image. The OD region is segmented using (i) a combination of active contour and morphological operations, (ii) a modified Chan-Vese algorithm and (iii) a combination of edge detection and ellipse fitting methods. The PPA region is identified from the presence of bright pixels in the temporal zone of the OD, and segmented using a sequence of techniques, including a modified Chan-Vese approach, thresholding, scanning filter and multi-seed region growing methods. The work demonstrates for the first time how the OD and PPA regions can be identified and quantified from 2D fundus images using a standard fundus camera.

This work is focused on automatic detection of optic disc in retinal images. There is briefly described anatomy of human eye, principles of retinal imaging and also overview of the methods used for optic disc detection. The practical part describes developed procedures for optic disc detection, ie detection based on watershed transform, active contours and also on region growing technique. The main method of this work is the method of circular transformation, which as the only one allowed to detect the optic disc on the images of video ophtalmoscope and also on the high quality images from fundus cameras. This method was tested on three datasets. The average overlap 92,44 % was achieved for HRF dataset, 91,03 for DRIONS dataset and 77,36 for images of video ophtalmoscope.

MMed, Ophthalmology,Faculty of Health Sciences, University of the Witwatersrand, 2009 / Objectives To determine in a cohort of 69 African patients with large optic discs and large optic cups, that proportion of patients with physiologic cupping (normal eyes) misdiagnosed as glaucomatous. To evaluate the possible relationship between optic disc size and central corneal thickness. Design and method A case series of 69 patients with large discs (vertical disc height measuring 1.8mm) and large cups (vertical cup to disc ratio 0.6) was evaluated to determine what proportion had glaucoma and what proportion was normal. Patients categorized as normal were further evaluated to determine what proportion were previously misdiagnosed and treated for glaucoma. Patients with a suspected diagnosis of glaucoma, normal tension glaucoma or primary open angle glaucoma were recruited from the glaucoma clinic at St John Eye Hospital. Outcome measures included corrected vertical disc height (VDH), vertical cup to disc ratio (CDR), central corneal thickness (CCT), the relationship between VDH and vertical cup height, the relationship between VDH and CCT, adjusted intraocular pressure (A-IOP), retinal nerve fiber layer analysis and visual fields. vii Results Sixty-nine African patients (138 eyes) with large discs and large cups were evaluated. 41 (59%) were females and 28 (41%) were males. The mean age was 56 years. Of the 69 patients, 51 (74%) had physiologic cupping (normal eyes) and 18 (26%) patients were glaucomatous. Of the group of 51 patients with physiologic cupping, there were 9 patients who were previously misdiagnosed with glaucoma and who had received treatment. VDH ranged between 1.9 and 3.2mm (mean ±SD, 2.3±0.26mm). The distribution analysis of VDH measurements noted the largest cluster around 2.3mm. CCT ranged between 454μm and 618μm (mean±SD, 516±37μm). 107 (77.5%) of the 138 eyes had CCT < 544μm. Conclusion Large cup to disc ratio in relation to large disc size can be normal. It can be misdiagnosed as glaucomatous if objective retinal nerve fiber layer analysis is not carried out. In this study, 9 (18%) patients from a group of 51 patients with physiologic cupping were misdiagnosed as glaucomatous. There was no linear correlation between CCT and VDH in this study. Pearson’s correlation coefficient was 0.13. The majority (77.5%) of eyes had thin corneas (CCT < 544μm).

This thesis present research work conducted in the field of retina image analysis. More specifically, the work is directed at the application of texture analysis technique for the segmentation of common retinal landmark and for retina image classification. The main challenge in this research is in identifying the suitable texture measurement for retina images. In this research we proposed the used of texture measurement based on Binary Robust Independent Elementary Features (BRIEF). BRIEF measure texture by performing an intensity comparison in a local image patch, thus it is very fast to compute and tolerant to any monotonic increase or decrease of image intensities, which makes the descriptor invariant to illumination. The performance of BRIEF as texture measurement is first shown in an experiment involving texture classification and segmentation using common texture datasets. The result demonstrates good performance from BRIEF in this experiment. BRIEF is next used in two applications of retinal image analysis, namely optic disc segmentation and glaucoma classification. In the former, we proposed the used of pixel classification using BRIEF as textural features and circular template matching to segment the optic disc. In addition, an extension of BRIEF called Rotation Invariant BRIEF (OBRIEF) is later proposed to improve the segmentation result. For glaucoma classification, we described two approaches for glaucoma classification using BRIEF/OBRIEF features. The first is based on determination of cup to disc ratio (CDR) and the second is classification using image features i.e. BRIEF features. Overall, our preliminary results on using BRIEF as texture measurement for retinal image analysis are encouraging and demonstrate that it has the potential to be used in retina image analysis.

Indiana University-Purdue University Indianapolis (IUPUI) / Hydrocephalus affects 1 in 1,000 newborns and nearly 1,000,000 Americans, leading to an increase in intercranial pressure due to the build-up of cerebrospinal fluid. There are numerous complications that arise as a result of hydrocephalus, but this study focuses on optic disc edema. The subarachnoid space surrounding the optic nerve contains cerebrospinal fluid. The cerebrospinal fluid increases in hydrocephalus, putting pressure on the optic nerve. The additional intracranial pressure has been proposed to cause axoplasmic stasis within the retinal ganglion cell axons, leading to axonal damage and retinal ischemia. The purpose of this study was to determine the effects of hydrocephalus on the optic disc and retina in several animal models of hydrocephalus. This study uses two genetic and two injury-induced models of hydrocephalus in addition to immunohistochemistry and histological stains to examine the optic disc, thickness of retinal layers, and numbers of retinal cells. This study serves as preliminary work to help build the case that hydrocephalus causes cell loss in the retina, as well as swelling of the retinal ganglion cell axons, leading to axoplasmic stasis and cell death. / Indefinitely

The main target of this work is a design of the program for border localization of the optic disc in OCT data. Part of this program is also localization of the „optic cup“ and calculation of several values that characterize optic disc. The work is also dealing with a description of the optical coherence tomography principle which is used in ophthalmology. One chapter describes some published methods of optic cup localization. Success of the program and its comparison with OCT Zeiss Stratus 3000 is evaluated at the end of the work.

The evaluation of retina structures has been of great interest because it could be used as a non-intrusive diagnosis in modern ophthalmology to detect many important eye diseases as well as cardiovascular disorders. A variety of retinal image analysis tools have been developed to assist ophthalmologists and eye diseases experts by reducing the time required in eye screening, optimising the costs as well as providing efficient disease treatment and management systems. A key component in these tools is the segmentation and quantification of retina structures. However, the imaging artefacts such as noise, intensity homogeneity and the overlapping tissue of retina structures can cause significant degradations to the performance of these automated image analysis tools. This thesis aims to provide robust and reliable automated retinal image analysis technique to allow for early detection of various retinal and other diseases. In particular, four innovative segmentation methods have been proposed, including two for retinal vessel network segmentation, two for optic disc segmentation and one for retina nerve fibre layers detection. First, three pre-processing operations are combined in the segmentation method to remove noise and enhance the appearance of the blood vessel in the image, and a Mixture of Gaussians is used to extract the blood vessel tree. Second, a graph cut segmentation approach is introduced, which incorporates the mechanism of vectors flux into the graph formulation to allow for the segmentation of very narrow blood vessels. Third, the optic disc segmentation is performed using two alternative methods: the Markov random field image reconstruction approach detects the optic disc by removing the blood vessels from the optic disc area, and the graph cut with compensation factor method achieves that using prior information of the blood vessels. Fourth, the boundaries of the retinal nerve fibre layer (RNFL) are detected by adapting a graph cut segmentation technique that includes a kernel-induced space and a continuous multiplier based max-flow algorithm. The strong experimental results of our retinal blood vessel segmentation methods including Mixture of Gaussian, Graph Cut achieved an average accuracy of 94:33%, 94:27% respectively. Our optic disc segmentation methods including Markov Random Field and Compensation Factor also achieved an average sensitivity of 92:85% and 85:70% respectively. These results obtained on several public datasets and compared with existing methods have shown that our proposed methods are robust and efficient in the segmenting retinal structures such the blood vessels and the optic disc.

Amblyopia is the leading cause of monocular visual impairment in children. Therapy for amblyopia is extremely beneficial in some children but ineffective in others. It is critical that the reasons for this discrepancy are understood. Emerging evidence indicates that current clinical protocols for the diagnosis of amblyopia may not be sufficiently sensitive in identifying individuals who, on more detailed examination, exhibit subtle structural defects of the eye. Presently, the magnitude of this problem is unknown. The aim of this study was to establish the prevalence of subtle retinal/optic nerve head defects in eyes diagnosed with amblyopia, to distinguish between possible explanations for the origin of such defects and to investigate the relationship between quantitative measures of retinal structure, retinal nerve fibre layer thickness and optic nerve head dimensions. Using the imaging technique of Optical Coherence Tomography (OCT) retinal structure has been investigated in detail, following the visual pathway across the retina from the fovea, via the paramacular bundle to the optic disc, where peripapillary retinal nerve fibre thickness has been imaged and subjected to detailed measures along with optic disc size and shape. The study formed two phases, the first imaging the eyes of visually normal adults and children, comparing them to amblyopes, both adults and children who had completed their treatment. The second phase, a longitudinal study, investigated retinal structure of amblyopic children undertaking occlusion therapy for the first time. By relating pre-therapy quantitative measures to the visual outcome the second phase of the study aimed to examine whether OCT imaging could identify children achieving a poor final outcome. The results show a clear picture of inter-ocular symmetry structure in all individuals, visually normal and amblyopic. Optic disc characteristics revealed no structural abnormalities in amblyopes, in any of the measured parameters, nor was there any association between the level of visual acuity and the measured structure. At the fovea differences were shown to occur in the presence of amblyopia, with thickening of the fovea and reduction of the foveal pit depth. The structural changes were found to be both bilateral and symmetrical with the fellow eye also affected. In the longitudinal phase of the study these changes were demonstrated to a greater extent in children who 'failed' to respond to treatment. This bilateral, symmetrical structural change found at the fovea, which has not been previously reported, cannot therefore be the primary cause of the visual loss which has been diagnosed as amblyopia.