The Use of Corneal Cross-linking in Treatment of Progressive Keratoconus: a Review

AbstractKeratoconus is a common corneal ectatic disorder which affects approximately 1 in 2,000 people. The traditional treatments for keratoconus are the use of inserts, deep anterior lamellar keratoplasty (DALK) and anterior lamellar keratoplasty (ALKP). Corneal cross-linking is a relatively new minimally invasive therapeutic approach for treatment of progressive keratoconus, which increases the structural integrity of the cornea. In corneal cross-linking the production of oxygen free radicals by ultraviolet A (UVA) light increases the biomechanical strength of cornea while riboflavin acts as a photo synthesizer for production of oxygen free radicals by UVA. Treatment of progressive keratoconus is the most widespread use of cross-linking technique. In the present manuscript we will summarize different aspects of the utilization of cross-linking in treatment of corneal keratoconus. Keywords: Corneal Cross-linking; Treatment; Progressive; Keratoconu

Les algorithmes de haute résolution en tomographie d'émission par positrons : développement et accélération sur les cartes graphiques

La tomographie d’émission par positrons (TEP) est une modalité d’imagerie moléculaire utilisant des radiotraceurs marqués par des isotopes émetteurs de positrons permettant de quantifier et de sonder des processus biologiques et physiologiques. Cette modalité est surtout utilisée actuellement en oncologie, mais elle est aussi utilisée de plus en plus en cardiologie, en neurologie et en pharmacologie. En fait, c’est une modalité qui est intrinsèquement capable d’offrir avec une meilleure sensibilité des informations fonctionnelles sur le métabolisme cellulaire. Les limites de cette modalité sont surtout la faible résolution spatiale et le manque d’exactitude de la quantification. Par ailleurs, afin de dépasser ces limites qui constituent un obstacle pour élargir le champ des applications cliniques de la TEP, les nouveaux systèmes d’acquisition sont équipés d’un grand nombre de petits détecteurs ayant des meilleures performances de détection. La reconstruction de l’image se fait en utilisant les algorithmes stochastiques itératifs mieux adaptés aux acquisitions à faibles statistiques. De ce fait, le temps de reconstruction est devenu trop long pour une utilisation en milieu clinique. Ainsi, pour réduire ce temps, on les données d’acquisition sont compressées et des versions accélérées d’algorithmes stochastiques itératifs qui sont généralement moins exactes sont utilisées. Les performances améliorées par l’augmentation de nombre des détecteurs sont donc limitées par les contraintes de temps de calcul. Afin de sortir de cette boucle et permettre l’utilisation des algorithmes de reconstruction robustes, de nombreux travaux ont été effectués pour accélérer ces algorithmes sur les dispositifs GPU (Graphics Processing Units) de calcul haute performance. Dans ce travail, nous avons rejoint cet effort de la communauté scientifique pour développer et introduire en clinique l’utilisation des algorithmes de reconstruction puissants qui améliorent la résolution spatiale et l’exactitude de la quantification en TEP. Nous avons d’abord travaillé sur le développement des stratégies pour accélérer sur les dispositifs GPU la reconstruction des images TEP à partir des données d’acquisition en mode liste. En fait, le mode liste offre de nombreux avantages par rapport à la reconstruction à partir des sinogrammes, entre autres : il permet d’implanter facilement et avec précision la correction du mouvement et le temps de vol (TOF : Time-Of Flight) pour améliorer l’exactitude de la quantification. Il permet aussi d’utiliser les fonctions de bases spatio-temporelles pour effectuer la reconstruction 4D afin d’estimer les paramètres cinétiques des métabolismes avec exactitude. Cependant, d’une part, l’utilisation de ce mode est très limitée en clinique, et d’autre part, il est surtout utilisé pour estimer la valeur normalisée de captation SUV qui est une grandeur semi-quantitative limitant le caractère fonctionnel de la TEP. Nos contributions sont les suivantes : - Le développement d’une nouvelle stratégie visant à accélérer sur les dispositifs GPU l’algorithme 3D LM-OSEM (List Mode Ordered-Subset Expectation-Maximization), y compris le calcul de la matrice de sensibilité intégrant les facteurs d’atténuation du patient et les coefficients de normalisation des détecteurs. Le temps de calcul obtenu est non seulement compatible avec une utilisation clinique des algorithmes 3D LM-OSEM, mais il permet également d’envisager des reconstructions rapides pour les applications TEP avancées telles que les études dynamiques en temps réel et des reconstructions d’images paramétriques à partir des données d’acquisitions directement. - Le développement et l’implantation sur GPU de l’approche Multigrilles/Multitrames pour accélérer l’algorithme LMEM (List-Mode Expectation-Maximization). L’objectif est de développer une nouvelle stratégie pour accélérer l’algorithme de référence LMEM qui est un algorithme convergent et puissant, mais qui a l’inconvénient de converger très lentement. Les résultats obtenus permettent d’entrevoir des reconstructions en temps quasi-réel que ce soit pour les examens utilisant un grand nombre de données d’acquisition aussi bien que pour les acquisitions dynamiques synchronisées. Par ailleurs, en clinique, la quantification est souvent faite à partir de données d’acquisition en sinogrammes généralement compressés. Mais des travaux antérieurs ont montré que cette approche pour accélérer la reconstruction diminue l’exactitude de la quantification et dégrade la résolution spatiale. Pour cette raison, nous avons parallélisé et implémenté sur GPU l’algorithme AW-LOR-OSEM (Attenuation-Weighted Line-of-Response-OSEM) ; une version de l’algorithme 3D OSEM qui effectue la reconstruction à partir de sinogrammes sans compression de données en intégrant les corrections de l’atténuation et de la normalisation dans les matrices de sensibilité. Nous avons comparé deux approches d’implantation : dans la première, la matrice système (MS) est calculée en temps réel au cours de la reconstruction, tandis que la seconde implantation utilise une MS pré- calculée avec une meilleure exactitude. Les résultats montrent que la première implantation offre une efficacité de calcul environ deux fois meilleure que celle obtenue dans la deuxième implantation. Les temps de reconstruction rapportés sont compatibles avec une utilisation clinique de ces deux stratégies.Positron emission tomography (PET) is a molecular imaging modality that uses radiotracers labeled with positron emitting isotopes in order to quantify many biological processes. The clinical applications of this modality are largely in oncology, but it has a potential to be a reference exam for many diseases in cardiology, neurology and pharmacology. In fact, it is intrinsically able to offer the functional information of cellular metabolism with a good sensitivity. The principal limitations of this modality are the limited spatial resolution and the limited accuracy of the quantification. To overcome these limits, the recent PET systems use a huge number of small detectors with better performances. The image reconstruction is also done using accurate algorithms such as the iterative stochastic algorithms. But as a consequence, the time of reconstruction becomes too long for a clinical use. So the acquired data are compressed and the accelerated versions of iterative stochastic algorithms which generally are non convergent are used to perform the reconstruction. Consequently, the obtained performance is compromised. In order to be able to use the complex reconstruction algorithms in clinical applications for the new PET systems, many previous studies were aiming to accelerate these algorithms on GPU devices. Therefore, in this thesis, we joined the effort of researchers for developing and introducing for routine clinical use the accurate reconstruction algorithms that improve the spatial resolution and the accuracy of quantification for PET. Therefore, we first worked to develop the new strategies for accelerating on GPU devices the reconstruction from list mode acquisition. In fact, this mode offers many advantages over the histogram-mode, such as motion correction, the possibility of using time-of-flight (TOF) information to improve the quantification accuracy, the possibility of using temporal basis functions to perform 4D reconstruction and extract kinetic parameters with better accuracy directly from the acquired data. But, one of the main obstacles that limits the use of list-mode reconstruction approach for routine clinical use is the relatively long reconstruction time. To overcome this obstacle we : developed a new strategy to accelerate on GPU devices fully 3D list mode ordered-subset expectation-maximization (LM-OSEM) algorithm, including the calculation of the sensitivity matrix that accounts for the patient-specific attenuation and normalisation corrections. The reported reconstruction are not only compatible with a clinical use of 3D LM-OSEM algorithms, but also lets us envision fast reconstructions for advanced PET applications such as real time dynamic studies and parametric image reconstructions. developed and implemented on GPU a multigrid/multiframe approach of an expectation-maximization algorithm for list-mode acquisitions (MGMF-LMEM). The objective is to develop new strategies to accelerate the reconstruction of gold standard LMEM (list-mode expectation-maximization) algorithm which converges slowly. The GPU-based MGMF-LMEM algorithm processed data at a rate close to one million of events per second per iteration, and permits to perform near real-time reconstructions for large acquisitions or low-count acquisitions such as gated studies. Moreover, for clinical use, the quantification is often done from acquired data organized in sinograms. This data is generally compressed in order to accelerate reconstruction. But previous works have shown that this approach to accelerate the reconstruction decreases the accuracy of quantification and the spatial resolution. The ordered-subset expectation-maximization (OSEM) is the most used reconstruction algorithm from sinograms in clinic. Thus, we parallelized and implemented the attenuation-weighted line-of-response OSEM (AW-LOR-OSEM) algorithm which allows a PET image reconstruction from sinograms without any data compression and incorporates the attenuation and normalization corrections in the sensitivity matrices as weight factors. We compared two strategies of implementation: in the first, the system matrix (SM) is calculated on the fly during the reconstruction, while the second implementation uses a precalculated SM more accurately. The results show that the computational efficiency is about twice better for the implementation using calculated SM on-the-fly than the implementation using pre-calculated SM, but the reported reconstruction times are compatible with a clinical use for both strategies

The Effect of Topical Betamethasone Eye Drops on Postoperative Haze among Patients Undergoing Corneal Collagen Cross-Linking: a Randomized, Double Blind Placebo Controlled Study

Objective: To evaluate the effect of topical betamethasone eye drops on postoperative haze among patients undergoing corneal collagen cross-linking (CXL). Patients and Methods: Patients with mild to moderate keratoconus, aged 18 to 30 years, who were a candidate for CXL treatment and had the evidence of disease progression based on topographic findings entered the present study. One eye of each patient randomly received betamethasone and topical antibiotics after CXL and the other eye received topical antibiotics and placebo in place of betamethasone. The eyes were compared regarding BCVA, UCVA, refraction, keratometric and pachymetric findings using Pentacam, as well as changes of corneal haze using confocal microscopy, before CXL as well as one month and six months after CXL. Results: There was no difference in BCVA, UCVA, refraction, keratometric and pachymetric findings between the two groups before and six months after surgery. Based on confocal findings, the difference in light reflectance intensity between the case and control groups was statistically significant in anterior (P = 0.021) and posterior (P = 0.017) corneal stroma one month postoperatively, indicating higher haze in the placebo group. This difference was also statistically significant in anterior (P = 0.001) mid (P = 0.002) and posterior (P = 0.002) stroma six months postoperatively.Conclusion: Betamethasone had no effect on visual acuity, refraction, keratometric and pachymetric findings six months after CXL. It reduced corneal haze in both the first and the sixth months postoperatively. Keywords: Keratoconus; Cornea; Cross-Linking; Haze; Betamethason

The Survey of Independency Status Living in Elderly Referring to Tehran Civil Servants Pension Organization in 2015

AbstractIntroduction: elderly is one of the most sensitive ages in everyone’s life, thus regarding the everyday growth of the elderly population, caring for this vulnerable part of society is a necessity. Having in mind the confronting limitations in this era and lack of flexibility with environment, as well as decreasing independency status in the elderly, this study aims at evaluatin the amount of independent living in the elderly referring to Tehran Civil Servants Pension Organization (C.S.P.O) in 2015.Methods and Materials: This descriptive study was conducted on 260 elderly people referring to Tehran Civil Servants Pension Organization. Samples are selected via sapling method available in Civil Servants. The obtained data in this study were collected by standard questionnaire, including demographic characteristics and physical activity questionnaire in two sections, i.e. Activity Daily Living and Instrumental Activity Daily Living. After completing two questionnaires, the obtained data were analyzed using SPSS (ver. 23) through descriptive statistics, independent t-test, as well as One-way Anova.Results: The total mean score of age for the studied objects was 68.08 ± (7.63) years. The total mean score of independence in this group of elderly people has been independent (ADL= 13.61±1.14 & IADL= 14.77±3.79). Moreover, the total mean score of independence living in elderly with aging 60-74 years with incomes above 750 to 1 million dollars per month and the elderly with married, were higher.Discussion And Conclusion: elderly is a normal stage in the normal path of life for human beings, which is very different from other life stages. In general with increasing age decrease the level of independent living, and consequently the degree of dependence on others increases in the elderly. Also the elderly married who lives with wife and children and have better economic situation are more independent than the other. furthermore the obtained data in the current study and other studies reveals that the elderly people have the highest amount of independence in Activity Daily Living such as eating and sleeping, and Instrumental Activity Daily Living such as taking medicine and using telephone

Environmental and geochemical characteristics of heavy metals in soils around the former mining area of zeïda (High Moulouya, Morocco)

The Zeïda mining center, closed in the mid-1980s, was once intensively exploited for lead concentrates. Throughout its activity, more than 12 Mt of tailings were generated and, to this day, they are still abandoned in the open air, exposed to weathering conditions without any rehabilitation. The purpose of the present study is to evaluate the environmental and geochemical characteristics of the soils, combining physicochemical, mineralogical, sequential, and kinetic extraction analyses, as well as the metallic spatial distribution and pollution indices of heavy metals (Pb, Cd, Cu, As, and Zn), levels, and risks. The results showed that the abandoned tailings had the highest concentrations of heavy metals, far exceeding their equivalents in the international and local guidelines. The soils spatial distribution maps showed that the levels of heavy metals decreased with distance from the tailings. Based on the pollution indices results, the soils located on and near the tailings are highly contaminated mainly by Pb. While downstream of the tailings, this contamination intensity decreased until becoming null. The sequential extraction results indicated that Pb, Zn, and Cd were primarily associated with the exchangeable fraction in tailings and soils. Therefore, they were more mobile and environmentally hazardous in the study area. The As was mainly associated with the residual fraction, and was thus immobile. Cu was more mobile in tailings as long as it was associated with the reducible fraction while it became immobile in the downstream soils. The kinetic extractions using EDTA and H2O revealed that the labile and less labile fractions were very significant in tailing for the majority of heavy metals. The methodology applied in this study may constitute a valuable tool to develop appropriate mine reclamation solution

An investigation of Hertzian contact in soft materials using photoelastic tomography

Hertzian contact of a rigid sphere and a highly deformable soft solid is investigated using integrated photoelasticity. The experiments are performed by pressing a styrene sphere of 15 mm diameter against a 44 x 44 x 47 mm$^3$ cuboid made of 5% wt. gelatin, inside a circular polariscope, and with a range of forces. The emerging light rays are processed by considering that the retardation of each ray carries the cumulative effect of traversing the contact-induced axisymmetric stress field. Then, assuming Hertzian theory is valid, the retardation is analytically calculated for each ray and compared to the experimental one. Furthermore, a finite element model of the process introduces the effect of finite displacements and strains. Beyond the qualitative comparison of the retardation fields, the experimental, theoretical, and numerical results are quantitatively compared in terms of the maximum equivalent stress, surface displacement, and contact radius dimensions. A favorable agreement is found at lower force levels, where the assumptions of Hertz theory hold, whereas deviations are observed at higher force levels. A major discovery of this work is that at the maximum equivalent stress location, all three components of principal stress can be determined experimentally, and show satisfactory agreement with theoretical and numerical ones in our measurement range. This provides valuable insight into Hertzian contact problems since the maximum equivalent stress controls the initiation of plastic deformation or failure. The measured displacement and contact radii also reasonably agree with the theoretical and numerical ones. Finally, the limitations that arise due to the linearization of this problem are explored

Ocular Graft Versus Host Disease Following Allogeneic Stem Cell Transplantation: A Review of Current Knowledge and Recommendations

Graft versus host disease (GVHD) is a common complication of allogeneic stem cell transplantation (allo-SCT). Ocular GVHD develops in approximately 40-60% of patients following allo-SCT and its most common clinical manifestations include keratoconjunctivitis sicca and cicatricial conjunctivitis. Ocular GVHD may lead to severe ocular surface disease, which can significantly diminish quality of life and restrict daily activities. It is thus important to monitor the condition closely since with timely diagnosis, irreversible damage can be avoided. The current review will focus on updated information regarding ocular GVHD

The Effect of Credit Allocation on Entrepreneurship

This paper aims to empirically assess Schumpeter's view that access to credit is vital for entrepreneurial activities. Credit allocation refers to the allocation of bank credits by the monetary authorities to non-financial economic activities. To measure the scope and penetration of entrepreneurship, two common indicators are used: The New Business Entry Density (ED) of the World Bank (WB) and Total Early-stage Entrepreneurial Activity (TEA) of the Global Entrepreneurship Monitor (GEM). Our sample for the first case includes 66 countries over the period 2006 to 2016, and for the second case, 54 countries during the period 2001 to 2016. The results rejects the hypothesis of the impacts of credit allocation on entrepreneurship in the case of former indicators, but do not reject it in the case of the latter indicators.  Furthermore, the sensitivity of the results to the choice of entrepreneurship measure indicates that further inquiries as well as alternative indicators are required to address the Schumpeterian hypothesis