Glaucoma, a leading cause of blindness worldwide, results in gradual vision loss if untreated due to retinal ganglion cell degeneration. Optical coherence tomography (OCT) machine measures retinal nerve fiber layers and the optic nerve head (ONH), with Považay et al. introducing the Pigment Epithelium – Inner limit of the retina Minimal Distance Averaged Over 2π Radians (PIMD-2π) for quantifying nerve fiber cross-sections. PIMD, defined as the distance between the Optic nerve head Pigment epithelium Central Limit (OPCL) and the Inner limit of the Retina Closest Point (IRCP), shows promise for earlier glaucoma detection compared to visual field assessments. The objective of this research is to enhance the Auto-PIMD program for calculating PIMD lengths in OCT images, aiding healthcare professionals in diagnosing glaucoma. Originally based on the 2D U-Net framework, this study proposes a replacement of the deep learning model framework and introduces a novel experimental procedure aimed at refining the accuracy of OPCLs calculation. Leveraging the nnU-Net model, commonly employed for semantic segmentation in medical imaging, the computational process entails segmenting vitreous masks and OPCLs. Utilizing a dataset of 78 OCT images provided by Uppsala University, experiments were conducted in both cylindrical domain (using 2D U-Net and nnU-Net cylindrical architecture) and Cartesian domain (nnU-Net Cartesian architecture). Qualitative and graphical analysis of the obtained OPCLs coordinate points demonstrates the nnU-Net frameworks' ability to yield points close to true voxel values(mean Euclidean distance of nnU-Net cylindrical architecture: 1.665; mean Euclidean distance of nnU-Net Cartesian architecture: 2.4495), contrasting with the higher uncertainties of the 2D U-Net architecture(mean Euclidean distance: 10.6827). Moreover, the nnU-Net Cartesian architecture eliminates human bias stemming from manual ONH center selection for cylindrical coordinate expansion. Examination of PIMD length calculations reveals all three methods effectively distinguishing between glaucoma patients and healthy subjects, with the nnU-Net-based methods displaying greater stability. This study contributes to refining OPCLs coordinate point accuracy and underscores the potential of the Auto-PIMD program in glaucoma diagnosis. / Glaukom, som är en av de främsta orsakerna till blindhet i världen, leder till gradvis synförlust om det inte behandlas på grund av degeneration av ganglieceller i näthinnan. Med optisk koherenstomografi (OCT) mäts nervfiberlagren i näthinnan och synnervshuvudet (ONH), och Považay et al. introducerade Pigmentepitel - Näthinnans inre gräns Minimal Distance Averaged Over 2π Radians (PIMD-2π) för att kvantifiera tvärsnitt av nervfibrer. PIMD, definierat som avståndet mellan den centrala gränsen (OPCL) för optikusnervhuvudets pigmentepitel och den inre gränsen för näthinnans närmaste punkt (IRCP), visar lovande resultat för tidigare upptäckt av glaukom jämfört med synfältsbedömningar. Syftet med denna forskning är att förbättra Auto-PIMD-programmet för beräkning av PIMD-längder i OCT-bilder, vilket hjälper vårdpersonal att diagnostisera glaukom. Denna studie, som ursprungligen baserades på 2D U-Net-ramverket, föreslår en ersättning av ramverket för djupinlärningsmodellen och introducerar ett nytt experimentellt förfarande som syftar till att förfina noggrannheten i OPCL-beräkningen. Med hjälp av nnU-Net-modellen, som ofta används för semantisk segmentering inom medicinsk bildbehandling, innebär beräkningsprocessen segmentering av glaskroppsmasker och OPCL. Med hjälp av ett dataset med 78 OCT-bilder från Uppsala universitet genomfördes experiment i både cylindrical domän (med 2D U-Net och nnU-Net cylindrical arkitektur) och kartesisk domän (nnU-Net kartesisk arkitektur). Kvalitativ och grafisk analys av de erhållna OPCL-koordinatpunkterna visar att nnU-Net-ramverken kan ge punkter som ligger nära sanna värden(genomsnittligt euklidiskt avstånd för nnU-Nets polära arkitektur: 1,665; genomsnittligt euklidiskt avstånd för nnU-Net kartesisk arkitektur: 2,4495), i motsats till de högre osäkerheterna i 2D U-Net-arkitekturen(genomsnittligt euklidiskt avstånd: 10,6827). Dessutom eliminerar den kartesiska arkitekturen i nnU-Net mänsklig partiskhet som härrör från manuellt val av ONH-centrum för polär koordinatexpansion. Granskning av PIMD-längdsberäkningar visar att alla tre metoderna effektivt skiljer mellan glaukompatienter och friska försökspersoner, där de nnU-Net-baserade metoderna uppvisar större stabilitet. Denna studie bidrar till att förbättra noggrannheten i OPCL:s koordinatpunkter och understryker potentialen i Auto-PIMD-programmet vid glaukomdiagnos.

The retina is a highly metabolically active tissue with large demands on the supply of nutrients. Disorders affecting the retina often include some vasculopathy with an impact on retinal circulation. Studies of retinal haemodynamics could thus help to detect, differentiate and diagnose diseases, to monitor changes in disease as well as progression and efficiency of the therapy. The present studies were an attempt to validate and determine the clinical usefulness of a newly developed technique for studying the retinal circulation in human eyes. We used different techniques to evaluate different parameters of retinal circulation. We examined how leukocyte velocity determined with Blue Field Simulation and transit times, mean transite time (MTT) and arterio-venous passage (AVP), and vessel diameter, determined from fluorescein angiograms, together reflects the retinal circulation. MTT was determined with a method based on an Impulse-Response technique, MTTIR. In a study on monkeys we compared our method, together with two conventional methods, with an absolute measurement of retinal blood flow (RBF) determined with labelled microspheres. There was a weak, but not statistically significant, correlation between retinal blood flow and MTTIR (r2 = -0.60, p = 0.06), but no useful correlation between retinal blood flow and either of the other two measures of transit times. In a study on healthy eyes we determined the effect of a physiological provocation, changes in arterial blood gases, on retinal circulation. Breathing pure oxygen or increased level of carbon dioxide in inspired air had no effect on MTT, but oxygen reduced leukocyte velocity and vessel diameter and carbon dioxide increased leukocyte velocity significantly. We concluded that unchanged transit time trough the retinal tissue was not due to a lack of effect of the gas provocation but a result due to concomitant changes in volume and flow. In a study on eyes of patients with diabetic retinopathy we investigated the relation between the extent of retinal circulation changes and the severity of the diabetes retinopathy (DRP). Transit times were relatively unaffected until proliferative DRP (PDRP) developed. In eyes with PDRP both MTTIR and AVP were increased. After panretinal photocoagulation treatment MTTIR returned to normal levels and vessel diameters tended to decrease while leukocyte velocity and AVP remained unchanged. We concluded that the increase in MTTIR in eyes with PDRP is at least partly explained by vessel dilation, causing an increased volume of the retinal vascular bed.