Superimposition of eye fundus images for longitudinal analysis from large public health databases

In this paper, a method is presented for superimposition (i.e. registration) of eye fundus images from persons with diabetes screened over many years for diabetic retinopathy. The method is fully automatic and robust to camera changes and colour variations across the images both in space and time. All the stages of the process are designed for longitudinal analysis of cohort public health databases where retinal examinations are made at approximately yearly intervals. The method relies on a model correcting two radial distortions and an affine transformation between pairs of images which is robustly fitted on salient points. Each stage involves linear estimators followed by non-linear optimisation. The model of image warping is also invertible for fast computation. The method has been validated (1) on a simulated montage and (2) on public health databases with 69 patients with high quality images (271 pairs acquired mostly with different types of camera and 268 pairs acquired mostly with the same type of camera) with success rates of 92% and 98%, and five patients (20 pairs) with low quality images with a success rate of 100%. Compared to two state-of-the-art methods, ours gives better results.Comment: This is an author-created, un-copyedited version of an article published in Biomedical Physics \& Engineering Express. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/2057-1976/aa7d1

Registration of retinal images from Public Health by minimising an error between vessels using an affine model with radial distortions

In order to estimate a registration model of eye fundus images made of an affinity and two radial distortions, we introduce an estimation criterion based on an error between the vessels. In [1], we estimated this model by minimising the error between characteristics points. In this paper, the detected vessels are selected using the circle and ellipse equations of the overlap area boundaries deduced from our model. Our method successfully registers 96 % of the 271 pairs in a Public Health dataset acquired mostly with different cameras. This is better than our previous method [1] and better than three other state-of-the-art methods. On a publicly available dataset, ours still better register the images than the reference method

Logarithmic mathematical morphology: a new framework adaptive to illumination changes

A new set of mathematical morphology (MM) operators adaptive to illumination changes caused by variation of exposure time or light intensity is defined thanks to the Logarithmic Image Processing (LIP) model. This model based on the physics of acquisition is consistent with human vision. The fundamental operators, the logarithmic-dilation and the logarithmic-erosion, are defined with the LIP-addition of a structuring function. The combination of these two adjunct operators gives morphological filters, namely the logarithmic-opening and closing, useful for pattern recognition. The mathematical relation existing between ``classical'' dilation and erosion and their logarithmic-versions is established facilitating their implementation. Results on simulated and real images show that logarithmic-MM is more efficient on low-contrasted information than ``classical'' MM

Potential Imaging Biomarkers in the Development and Progression of Diabetic Retinopathy

Diabetic retinopathy (DR) is the most prevalent microvascular complication of diabetes and a leading cause of preventable blindness in the working-age population. However, due to a lack of suitable biomarkers, its prediction in asymptomatic patients is insufficient. Currently, DR is diagnosed at a stage when typical morphologic lesions become fundoscopically visible. Yet, chronically elevated blood glucose levels lead to characteristic alterations in retinal vessel caliber, blood flow, oxygen saturation, and the capillary network, which precede DR lesions. Furthermore, emerging evidence suggests that retinal neurodegenerative changes occur early in diabetes, initiating a disintegration of the retinal neurovascular unit prior to the appearance of microvasculopathy in DR. This chapter will discuss recent research achievements toward understanding the complexities of DR pathophysiology. It will focus on the nomination of potential imaging biomarkers for the prediction of DR development and progression using innovative structural, functional, and metabolic imaging techniques, including optical coherence tomography angiography (OCTA), retinal oximetry, ultra-wide field FA, and corneal confocal microscopy (CCM). Validation of these biomarkers would allow the identification of patients at high risk of developing DR and might initiate a swift move to early diagnosis and individualized care

Visual field and structural alterations in age-related macular degeneration

The thesis investigated progression of the central 10° visual field with structural changes at the macula in a cross-section of patients with varying degrees of agerelated macular degeneration (AMD). The relationships between structure and function were investigated for both standard and short-wavelength automated perimetry (SWAP). Factors known to influence the measure of visual field progression were considered, including the accuracy of the refractive correction on SWAP thresholds and the learning effect. Techniques of assessing the structure to function relationships between fundus images and the visual field were developed with computer programming and evaluated for repeatability. Drusen quantification of fundus photographs and retro-mode scanning laser ophthalmoscopic images was performed. Visual field progression was related to structural changes derived from both manual and automated methods. Principal Findings: • Visual field sensitivity declined with advancing stage of AMD. SWAP showed greater sensitivity to progressive changes than standard perimetry. • Defects were confined to the central 5°. SWAP defects occurred at similar locations but were deeper and wider than corresponding standard perimetry defects. • The central field became less uniform as severity of AMD increased. SWAP visual field indices of focal loss were of more importance when detecting early change in AMD, than indices of diffuse loss. • The decline in visual field sensitivity over stage of severity of AMD was not uniform, whereas a linear relationship was found between the automated measure of drusen area and visual field parameters. • Perimetry exhibited a stronger relationship with drusen area than other measures of visual function. • Overcorrection of the refraction for the working distance in SWAP should be avoided in subjects with insufficient accommodative facility. • The perimetric learning effect in the 10° field did not differ significantly between normal subjects and AMD patients. • Subretinal deposits appeared more numerous in retro-mode imaging than in fundus photography

Quality-of-life and clinical outcomes in age-related macular degeneration

Age-related macular degeneration (AMD) is of increasing concern given the ageing population, and the associated economic and social burdens. Vision-related quality-of-life (QoL) is arguably one of the most important factors in the management of those with AMD. Consequently, there is a clear need for an understanding of the clinical outcomes that influence vision-related QoL in order to inform management strategies. The principle aim of the studies described herein was to determine the factors that predict vision-related QoL in those with AMD, over 1 year. Experimental procedures were undertaken at baseline (n=52 individuals with AMD) and repeated after 1 year (n=32 individuals with AMD). These included: visual acuity, contrast sensitivity, reading speed, microperimetry, optical coherence tomography and fundus photography. A questionnaire interview included assessment of vision-related QoL (Impact of Visual Impairment questionnaire), health status (EQ-5D), level of depressive symptoms (PHQ-9) and well-being (Warwick-Edinburgh Well-Being Scale). At baseline, the optimum multiple regression model accounted for 41% of the variance in vision-related QoL and included Mean Total Deviation or Mean Sensitivity with level of depressive symptoms. After 1 year, the optimum model to predict change in vision-related QoL accounted for 43% of the variance and included baseline contrast sensitivity and change in health status and reading speed. The most clinically useful measures of visual function, in identifying those with a reduced QoL or those at risk of a reduced QoL were contrast sensitivity, microperimetry, and reading speed. These outcomes may allow a better understanding of vision-related QoL if they were adopted in a clinical setting. In conclusion, the studies provide sufficient evidence to encourage a review of the clinical outcome measures most relevant to vision-related QoL

Visual field and structural alterations in age-related macular degeneration

The thesis investigated progression of the central 10° visual field with structural changes at the macula in a cross-section of patients with varying degrees of agerelated macular degeneration (AMD). The relationships between structure and function were investigated for both standard and short-wavelength automated perimetry (SWAP). Factors known to influence the measure of visual field progression were considered, including the accuracy of the refractive correction on SWAP thresholds and the learning effect. Techniques of assessing the structure to function relationships between fundus images and the visual field were developed with computer programming and evaluated for repeatability. Drusen quantification of fundus photographs and retro-mode scanning laser ophthalmoscopic images was performed. Visual field progression was related to structural changes derived from both manual and automated methods. Principal Findings: • Visual field sensitivity declined with advancing stage of AMD. SWAP showed greater sensitivity to progressive changes than standard perimetry. • Defects were confined to the central 5°. SWAP defects occurred at similar locations but were deeper and wider than corresponding standard perimetry defects. • The central field became less uniform as severity of AMD increased. SWAP visual field indices of focal loss were of more importance when detecting early change in AMD, than indices of diffuse loss. • The decline in visual field sensitivity over stage of severity of AMD was not uniform, whereas a linear relationship was found between the automated measure of drusen area and visual field parameters. • Perimetry exhibited a stronger relationship with drusen area than other measures of visual function. • Overcorrection of the refraction for the working distance in SWAP should be avoided in subjects with insufficient accommodative facility. • The perimetric learning effect in the 10° field did not differ significantly between normal subjects and AMD patients. • Subretinal deposits appeared more numerous in retro-mode imaging than in fundus photography.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

REGION HOMOGENEITY IN THE LOGARITHMIC IMAGE PROCESSING FRAMEWORK: APPLICATION TO REGION GROWING ALGORITHMS

In order to create an image segmentation method robust to lighting changes, two novel homogeneity criteria of an image region were studied. Both were defined using the Logarithmic Image Processing (LIP) framework whose laws model lighting changes. The first criterion estimates the LIP-additive homogeneity and is based on the LIP-additive law. It is theoretically insensitive to lighting changes caused by variations of the camera exposure-time or source intensity. The second, the LIP-multiplicative homogeneity criterion, is based on the LIP-multiplicative law and is insensitive to changes due to variations of the object thickness or opacity. Each criterion is then applied in Revol and Jourlin’s (1997) region growing method which is based on the homogeneity of an image region. The region growing method becomes therefore robust to the lighting changes specific to each criterion. Experiments on simulated and on real images presenting lighting variations prove the robustness of the criteria to those variations. Compared to a state-of the art method based on the image component-tree, ours is more robust. These results open the way to numerous applications where the lighting is uncontrolled or partially controlled

Biometrics

Biometrics uses methods for unique recognition of humans based upon one or more intrinsic physical or behavioral traits. In computer science, particularly, biometrics is used as a form of identity access management and access control. It is also used to identify individuals in groups that are under surveillance. The book consists of 13 chapters, each focusing on a certain aspect of the problem. The book chapters are divided into three sections: physical biometrics, behavioral biometrics and medical biometrics. The key objective of the book is to provide comprehensive reference and text on human authentication and people identity verification from both physiological, behavioural and other points of view. It aims to publish new insights into current innovations in computer systems and technology for biometrics development and its applications. The book was reviewed by the editor Dr. Jucheng Yang, and many of the guest editors, such as Dr. Girija Chetty, Dr. Norman Poh, Dr. Loris Nanni, Dr. Jianjiang Feng, Dr. Dongsun Park, Dr. Sook Yoon and so on, who also made a significant contribution to the book