1,721,156 research outputs found
Systematic Review on Fractal Dimension of the Retinal Vasculature in Neurodegeneration and Stroke: Assessment of a Potential Biomarker
No full textIntroduction: Ocular manifestations in several neurological pathologies accentuate the strong relationship between the eye and the brain. Retinal alterations in particular can serve as surrogates for cerebral changes. Offering a "window to the brain," the transparent eye enables non-invasive imaging of these changes in retinal structure and vasculature. Fractal dimension (FD) reflects the overall complexity of the retinal vasculature. Changes in FD could reflect subtle changes in the cerebral vasculature that correspond to preclinical stages of neurodegenerative diseases. In this review, the potential of this retinal vessel metric to serve as a biomarker in neurodegeneration and stroke will be explored. Methods: A literature search was conducted, following the PRISMA Statement 2009 criteria, in four large bibliographic databases (Pubmed, Embase, Web Of Science and Cochrane Library) up to 12 October 2019. Articles have been included based upon their relevance. Wherever possible, level of evidence (LOE) has been assessed by means of the Oxford Centre for Evidence-based Medicine Level of Evidence classification. Results: Twenty-one studies were included for qualitative synthesis. We performed a narrative synthesis and produced summary tables of findings of included papers because methodological heterogeneity precluded a meta-analysis. A significant association was found between decreased FD and neurodegenerative disease, mainly addressing cognitive impairment (CI) and dementia. In acute, subacute as well as chronic settings, decreased FD seems to be associated with stroke. Differences in FD between subtypes of ischemic stroke remain unclear. Conclusions: This review provides a summary of the scientific literature regarding the association between retinal FD and neurodegenerative disease and stroke. Central pathology is associated with a decreased FD, as a measure of microvascular network complexity. As retinal FD reflects the global integrity of the cerebral microvasculature, it is an attractive parameter to explore. Despite obvious concerns, mainly due to a lack of methodological standardization, retinal FD remains a promising non-invasive and low-cost diagnostic biomarker for neurodegenerative and cerebrovascular disease. Before FD can be implemented in clinic as a diagnostic biomarker, the research community should strive for uniformization and standardization.sponsorship: SL has received a Ph.D. grant from VITO to performa joint Ph.D. between VITO and UZ Leuven. (VITO)status: Publishe
Ocular blood flow in glaucoma - the Leuven Eye Study
No full textElevated intra-ocular pressure (IOP) has been identified as a major risk factor for glaucoma. Additionally, extensive literature depicts a vascular dysfunction to exist in these patients. However, a large ocular blood flow-oriented trial to integrate these findings in the clinical setting is lacking. This study would likely help to identify which of these vascular data can be used as a clinical tool for screening and disease stratification.status: Publishe
Pathological myopia classification with simultaneous lesion segmentation using deep learning
No full textBACKGROUND AND OBJECTIVES: Pathological myopia (PM) is the seventh leading cause of blindness, with a reported global prevalence up to 3%. Early and automated PM detection from fundus images could aid to prevent blindness in a world population that is characterized by a rising myopia prevalence. We aim to assess the use of convolutional neural networks (CNNs) for the detection of PM and semantic segmentation of myopia-induced lesions from fundus images on a recently introduced reference data set. METHODS: This investigation reports on the results of CNNs developed for the recently introduced Pathological Myopia (PALM) dataset, which consists of 1200 images. Our CNN bundles lesion segmentation and PM classification, as the two tasks are heavily intertwined. Domain knowledge is also inserted through the introduction of a new Optic Nerve Head (ONH)-based prediction enhancement for the segmentation of atrophy and fovea localization. Finally, we are the first to approach fovea localization using segmentation instead of detection or regression models. Evaluation metrics include area under the receiver operating characteristic curve (AUC) for PM detection, Euclidean distance for fovea localization, and Dice and F1 metrics for the semantic segmentation tasks (optic disc, retinal atrophy and retinal detachment). RESULTS: Models trained with 400 available training images achieved an AUC of 0.9867 for PM detection, and a Euclidean distance of 58.27 pixels on the fovea localization task, evaluated on a test set of 400 images. Dice and F1 metrics for semantic segmentation of lesions scored 0.9303 and 0.9869 on optic disc, 0.8001 and 0.9135 on retinal atrophy, and 0.8073 and 0.7059 on retinal detachment, respectively. CONCLUSIONS: We report a successful approach for a simultaneous classification of pathological myopia and segmentation of associated lesions. Our work was acknowledged with an award in the context of the "Pathological Myopia detection from retinal images" challenge held during the IEEE International Symposium on Biomedical Imaging (April 2019). Considering that (pathological) myopia cases are often identified as false positives and negatives in glaucoma deep learning models, we envisage that the current work could aid in future research to discriminate between glaucomatous and highly-myopic eyes, complemented by the localization and segmentation of landmarks such as fovea, optic disc and atrophy.sponsorship: The first author is jointly supported by the Research Group Ophthalmology, KU Leuven and VITO NV. This research received funding from the Flemish Government under the "Onderzoeksprogramma Artificiele Intelligentie (AI) Vlaanderen" programme. No outside entities have been involved in the study design, in the collection, analysis and interpretation of data, in the writing of the manuscript, nor in the decision to submit the manuscript for publication. Thus, the authors declare that there are no conflicts of interest in this work. (Research Group Ophthalmology, VITO NV, Flemish Government, KU Leuven)status: Published onlin
Matrix metalloproteinasen in glaucoom: doelwitten voor nieuwe therapieën?
No full textMatrix metalloproteinases (MMPs), a family of Zn2+-dependent proteases, were originally named after their ability to cleave and remodel the extracellular matrix (ECM), however, their substrate repertoire has proven to be much broader, comprising other proteinases, growth factors, signaling molecules, cell surface receptors, and even intracellular targets. By proteolytic cleavage, MMPs modify the structure and activity of these substrates, and add a complex extra dimension of biological control. As a result, MMPs are important regulatory nodes in the protease web, a complex network of interactions that regulates protease activities and determines the functional state of the proteome and cell activity. Deregulated MMP activity is a common characteristic of many diseases, including neurodegenerative disorders such as glaucoma, multiple sclerosis, Huntington’s disease, Alzheimer’s disease, Parkinson’s disease, etc. Nevertheless, despite their detrimental impact during central nervous system (CNS) pathology, there is ample evidence corroborating MMPs as fine regulators of CNS physiology, and well-balanced MMP activity is instrumental to CNS development, plasticity and repair.
Multiple studies in glaucoma patients and in animal models of spontaneous and experimentally induced glaucoma, reported changes in the expression and activity of several MMPs in the retina, optic nerve, aqueous humor and trabecular meshwork. These data have led to the hypothesis that MMPs might be involved in glaucoma onset and/or disease progression. However, reports are conflicting and research aiming at providing a clear definition of their causative role is lacking. With this work, we intend to contribute to a better understanding of the role of MMPs during glaucoma pathogenesis and to the development of much-needed novel therapeutic approaches to treat this optic neuropathy. Indeed, with more than 65 million patients worldwide, and still on the increase, glaucoma is and will be a major concern for ophthalmologists today and in the future. Current baroprotective therapies allow to reduce intraocular pressure in the majority of glaucoma patients and to halt -yet not reverse- disease progression. Nevertheless, a sizeable percentage of patients do not benefit from this therapeutic approach, and, as no alternatives are available, experience progressive vision loss.
Four MMPs, namely MMP-2, MMP-3, MMP-9 and MT1-MMP, are the subject of different experimental approaches, aiming to answer the central question: “Can we identify MMPs as novel targets for the development of baroprotective, neuroprotective and/or regenerative therapeutic strategies for the treatment of glaucoma?”status: Publishe
ROCK Inhibition as a Versatile Strategy for the Treatment of Glaucoma
No full textGlaucoma is a chronic optic neuropathy which is characterized by the loss of retinal ganglio n cells, resulting in irreversible visual field lo ss. It is the most important cause of irreversible¨blindness worldwide and with aging of the populat ion the number of glaucoma patients is still expan ding. Mostly the appearance of this disease i s correlated with an increased intraocular pressur e (IOP), due to an imbalance between aqueous humor ¨production and outflow. Currently, lowering IOP i s the main treatment modality for glaucoma. A ¨sustained reduction of IOP can be achieved with m edical therapy, laser treatment or surgical i nterventions. First choice treatment for glau coma is medical therapy with IOP-lowering eye drop s. Despite the fact that there are several cl asses of glaucoma medications available, none ¨of them directly targets the trabecular meshwork, ¨which represents the main outflow route in t he human eye. Experimental evidence indicate s that the Rho kinase (ROCK) pathway is direc tly involved in the regulation of trabecular outflow. As such, targeting this pathway could pot entially lead to an improved IOP control for the m edical treatment of glaucoma.
Therefore, in the first part of this PhD projec t we investigated the IOP-lowering potential of AM A0076, a novel locally acting ROCK inhibitor. We d emonstrated that AMA0076 is a potent ROCK inhibito r with an IOP-lowering efficacy comparable to a re ference ROCK inhibitor, Y-39983. While the efficac y profile of ROCK inhibitors is promising, they ar e associated with significant ocular hyperemia due to conjunctival vasodilatation. Howeve r, due to its local mode of action AMA0076 induces ¨almost no conjunctival hyperemia in contrast to Y -39983. As such, AMA0076 clearly has an improved t olerability profile with respect to hyperemia comp ared to other ROCK inhibitors. We also compar ed the IOP-lowering effect of AMA0076 to prostagla ndin analogues (PGAs) because these are the most i mportant treatment modality in the medicinal treatment of glaucoma. Our results revealed that the IO P-lowering efficacy of AMA0076 is equivalent¨ to latanoprost in ocular normotensive rabbits . In a rabbit model of ocular hypertension, A MA0076 was even more potent in preventing IOP elev ation compared to PGAs (bimatoprost and latanopros t).
Taken together, these r esults indicate that ROCK inhibitors, and esp ecially AMA0076, may be promising new candidates a s novel IOP-lowering agents for the treatment glau coma.
Surgical interv ention is an important treatment modality for glau coma when other IOP-lowering measures (medical or¨ laser) are inadequate. However, there is a high ri sk of surgical failure due to excessive subco njunctival wound healing, causing obstruction of t he filtration channel by scar tissue. While the in troduction of antimitotics tremendously improved s urgical success, this has come at the cost of an i ncreased risk at postoperative complications due t o their nonspecific mechanism of action. Hence, th ere is an urgent need for novel, more specific and ¨safer agents to prevent glaucoma filtration failu re and improve surgery outcome. In the secon d part of this project, we investigated the effect ¨of ROCK inhibitor AMA0526 on the wound healing re sponse after glaucoma filtration surgery and its s ubsequent effect on surgical outcome. Our in v itro results showed that the ROCK inhibitor,¨ AMA0526, inhibited proliferation of tenon fib roblasts and fibroblast-to-myofibroblast diff erentiation. Using a rabbit model of glaucoma filtration surgery, we subsequently showed that p ostoperative treatment with the ROCK inhibitor sig nificantly improved glaucoma filtration surgery ou tcome. ROCK inhibition reduced postoperative infla mmation, angiogenesis and fibrosis. These results suggest that ROCK inhibitors are involved at¨ different levels in the process of wound healing a nd therefore may be considered as useful agents to ¨improve the success rate of glaucoma filtration surgery.
Evidence from large scale¨ clinical trials indicated that lowering IOP does n ot prevent glaucomatous progression in all patient s and that progression can continue despite e ffective IOP-lowering. These inadequacies in our c urrent treatment paradigm of this still blinding d isease have encouraged research to investigate neu roprotection as an alternative treatment strategy¨ for glaucoma. However, no neuroprotective therapy¨ is currently available to halt glaucomatous damage . Therefore, in the last part of this project we e laborately reviewed the high potential of the ¨Rho-ROCK pathway as a potential neuroprotective t arget for future management of glaucoma disease pr ogression. Our review indicates that there is ¨increasing evidence that ROCK inhibition can ¨promote RGC survival, and axon regeneration, demo nstrating the neuroprotective potential of ROCK in hibition for the treatment of glaucoma.
In conclusion, in this dissertation w e demonstrated that AMA0076 is a potent ROCK inhib itor with strong IOP-lowering capacity that does n ot induce distinct hyperemia. Secondly, we also sh owed that ROCK inhibition may serve as anti-s carring strategy after glaucoma filtration surgery ¨due to its inhibitory effect on inflammation , angiogenesis and fibrosis. Furthermore, the Rho- ROCK pathway is involved in optic nerve neuroprote ction. Earlier research showed that inactivat ion of ROCK increases survival and axon regen eration of RGCs. Considering the IOP lowering, ant i-scarring and neuroprotective properties of ROCK inhibitors, targeting the Rho-ROCK pathway wi th selective inhibitors may be a versatile and att ractive treatment option for glaucoma.status: Publishe
Deep learning on fundus images detects glaucoma beyond the optic disc
No full textAbstract Although unprecedented sensitivity and specificity values are reported, recent glaucoma detection deep learning models lack in decision transparency. Here, we propose a methodology that advances explainable deep learning in the field of glaucoma detection and vertical cup-disc ratio (VCDR), an important risk factor. We trained and evaluated deep learning models using fundus images that underwent a certain cropping policy. We defined the crop radius as a percentage of image size, centered on the optic nerve head (ONH), with an equidistant spaced range from 10–60% (ONH crop policy). The inverse of the cropping mask was also applied (periphery crop policy). Trained models using original images resulted in an area under the curve (AUC) of 0.94 [95% CI 0.92–0.96] for glaucoma detection, and a coefficient of determination (R2) equal to 77% [95% CI 0.77–0.79] for VCDR estimation. Models that were trained on images with absence of the ONH are still able to obtain significant performance (0.88 [95% CI 0.85–0.90] AUC for glaucoma detection and 37% [95% CI 0.35–0.40] R2 score for VCDR estimation in the most extreme setup of 60% ONH crop). Our findings provide the first irrefutable evidence that deep learning can detect glaucoma from fundus image regions outside the ONH
The Prevalence of Undiagnosed Age-Related Sight-Threatening Diseases in Self-Proclaimed Healthy Individuals
No full textBackground. Age-related conditions such as glaucoma, age-related macular degeneration, diabetic retinopathy, and cataract have become the major cause of visual impairment and blindness in high-income countries. The aim of the current study is to investigate the prevalence of these eye diseases in a cohort of self-proclaimed healthy elderly and thus get a rough estimation of the prevalence of undiagnosed age-related eye conditions in the Belgian population. Methods. Individuals aged 55 and older without ophthalmological complaints were asked to fill in a general medical questionnaire and underwent an ophthalmological examination, which included a biomicroscopic examination, intraocular pressure measurement, axial length measurement, and acquisition of fundus pictures and optical coherence tomography scans. Information regarding follow-up was collected in those who received the advice of referral to an ophthalmologist or the advice to have more frequent follow-up visits, based on their study evaluation. Results. The cohort included 102 people and comprised 46% men (median age 70 years, range 57-85 years). Referral for additional examinations was made in 26 participants (25%). The advice to have more regular follow-up ophthalmologist visits was given to nine additional participants (9%). No significant correlations between baseline characteristics and the need for referral could be identified. Follow-up information was available for 25 out of 26 referred volunteers. Out of these, four underwent a therapeutic intervention based on study referral, up until 18 months after study participation. All four interventions took place in the age group 65-74 years. Conclusions. This study shows that, even in an elderly population with self-proclaimed healthy eyes and good general health, a significant proportion of subjects showed ocular findings that need regular follow-up and/or intervention. The frequency of prior ophthalmological examinations does not seem to be relevant to this proportion, meaning that everyone above 55 years old needs a routine ophthalmological evaluation.The authors would like to thank Professor Emeritus Alfons Verbruggen for the recruitment support and Ms. Sien Boons, Ms. Freya Cachet, and Ms. Sarah Spileers for the administrative support to this study. Sophie Lemmens is holder of a joint VITO-UZ Leuven PhD grant.Lemmens, S (corresponding author), Univ Hosp UZ Leuven, Dept Ophthalmol, Herestr 49, B-3000 Louvain, Belgium ; Katholieke Univ Leuven, Dept Neurosci, Res Grp Ophthalmol, Herestr 49, B-3000 Leuven, Belgium ; VITO Flemish Inst Technol Res, Hlth Unit, Boeretang 200, B-2400 Mol, Belgium.
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Venous circulation in glaucoma
No full textTese de doutoramento, Medicina (Oftalmologia), Universidade de Lisboa, Faculdade de Medicina, 2012A pulsatilidade venosa espontânea (SVP) da veia central da retina (CRV) é um sinal oftalmológico conhecido há mais de um século. Apesar da sua utilidade ser já reconhecida em várias doenças do foro neurológico e oftalmológico, trabalhos recentes têm sugerido que poderá também ter relevância em doentes com glaucoma. Os mecanismos envolvidos na formação deste sinal não são consensuais, existindo várias teorias sobre a sua génese. Esta ausência de consensos tem levado a várias hipóteses sobre o porquê da baixa frequência desta SVP em doentes com glaucoma (glaucoma primário de ângulo aberto – POAG) quando comparados com a população em geral. O nosso estudo prospectivo, caso-controlo apresenta a maior série publicada sobre o tema, incluindo o uso de tecnologias e variáveis ainda não estudadas neste contexto. Mais ainda, pela primeira vez foram estudados doentes em que a componente vascular terá um componente significativo na patogénese e evolução da doença (doentes com glaucoma normotensional – NTG). O nosso trabalho confirmou a diminuição significativa na identificação da SVP quer em doentes POAG (50%), quer em doentes NTG (51%) quando comparados com a população controlo (82%). Não se verificaram contudo diferenças na prevalência deste fenómeno entre os dois grupos com glaucoma. O facto mais interessante do nosso trabalho será talvez o facto de nos doentes com NTG, a ausência de SVP associar-se a danos funcionais significativamente mais avançados do que a verificada nos doentes NTG com SVP. A ausência deste sinal ao exame objectivo, ao indentificar doentes com patologia mais avançada, poderá ser particularmente útil na avaliação clínica dos doentes com esta forma da doença. Os nossos resultados sugerem ainda que esta diferença poderá estar associada a alterações da actividade metabólica das células ganglionares da retina, uma vez que apesar das diferenças funcionais, não registámos diferenças estruturais na camada de fibras nervosas retinianas. A verificação do fenómeno SVP não se correlacionou com nenhuma variável morfológica das topografias da cabeça do nervo óptico, quer em indivíduos saudáveis quer em doentes com glaucoma. Como um aumento da escavação do disco óptico influencia necessariamente o trajecto e grau de curvatura dos vasos papilares (e consequentemente os padrões de fluxo intraluminal), os nossos resultados parecem sugerir que alterações de fluxo assim induzidas serão insuficientes para modificar o status SVP. Para os mesmos intervalos de IOP, os doentes com glaucoma apresentam um registo menor de doentes com SVP. No entanto, nos doentes com POAG, um aumento deste factor mecânico está associado a uma maior prevalência do fenómeno, enquando que nos doentes com NTG essa prevalência não é alterada, o que parece sugerir que a ausência deste fenómeno nesta população não se deverá a factores mecânicos intraoculares. As pressões extraoculares, avaliadas indirectamente pelo diâmetro da bainha do nervo óptico (ONSD), parecem ter um impacto diferente nos vários grupos experimentais. Em indivíduos controlo, maiores ONSD estiveram associadas a uma menor frequência de detecção do fenómeno. Nos grupos com glaucoma, apesar das menores frequências de registo, essa prevalência não é alterada ao longo dos valores de ONSD. Estes doentes NTG sem SVP têm contudo uma associação importante com o ONSD, na medida em que se parece correlacionar positivamente com a IOP. Os nossos resultados parecem assim sugerir que neste tipo de glaucoma, a drenagem do humor aquoso pelo sistema venoso poderá ser particularmente sensível a alterações das pressões orbitárias retro-oculares. As duas populações de glaucoma apresentaram ainda correlações distintas com esta variável (ONSD), em que apenas doentes com POAG sem SVP apresentaram uma correlação entre o ONSD e as velocidades de fluxo dos vasos centrais da retina. Os nossos resultados sugerem assim que a veia central da retina (CRV) dos doentes com POAG poderá ser mais susceptível a uma compressão extrínseca, particularmente se esta for aplicada a jusante do ponto major de obstrução do vaso (a passagem pela lamina crivosa). Os doentes com NTG, em que possivelmente se regista uma alteração do microambiente no que diz respeito aos agentes vasoactivos, poderão apresentar uma alteração estrutural dos vasos – provavelmente hipertrofia da parede vascular – e consequentemente menos maleáveis a pressões externas. Estes estudos com Eco-Doppler dos vasos centrais da retina identificaram que os doentes NTG sem SVP apresentaram menores velocidades arteriais e venosas, enquanto que os doentes com POAG registaram apenas alterações venosas. Uma vez que a associação a um estadio de doença glaucomatosa mais avançada apenas se observou nos doentes em que co-existiam alterações arteriais e venosas, os nossos resultados parecem sugerir que ainda que a ausência de SVP possa estar associada a alterações venosas, apenas existindo um envolvimento arterial se verifique a associação a com maior dano glaucomatoso A análise efectuada das frentes da onda Doppler da artéria oftálmica (OA) identificou diferenças entre os grupos, reforçando a hipótese de existirem variações estruturais ao nível da parede dos vasos entre os doentes NTG com e sem SVP. Os nossos dados não sustentam que o status SVP identifique limiares de resistência vasculares que têm sido sugerido como limiares de autoregulação vascular nos doentes com glaucoma. Na medida em que os limiares utilizados parecem reflectir uma incapacidade de adaptação por parte dos capilares a condições de hipoperfusão, o status SVP poderá reflectir, não uma disfunção capilar, mas uma disfunção arterial e venosa ainda não esclarecida. Do ponto de vista hemodinâmico, a única diferença identificada nos indivíduos controlo foi um aumento das velocidades mínimas da veia central da retina (Vmin) nos indivíduos sem SVP. Este padrão tem sido descrito em situações de estase venosa no restante organismo. Estudos adicionais serão ainda necessários para validar esta teoria. Outro dado interessante do nosso trabalho é a associação nos doentes POAG entre a ausência de SVP e maiores valores de pressão arterial diastólica. Dado este ser um factor de risco conhecido no desenvolvimento da oclusão da CRV, a ausência deste sinal em doentes POAG poderá identificar os doentes com glaucoma em maior risco de desenvolverem esta patologias vascular. Serão contudo necessários estudos com maior follow-up para confirmar esta suspeita. As limitações do nosso estudo estão condicionadas por falhas metodológicas e insuficiências tecnológicas. O nosso estudo de caso-controlo carece de informação sobre a medicação sistémica e baseia-se na descrição pelo próprio dos seus antecedentes médicos sistémicos e oftalmológicos. Adicionalmente, as limitações referentes a qualquer estudo doppler retrobulbar (em que não é possível extrair dados referentes ao diâmetro dos vasos analisados) bem como a incapacidade de clinicamente avaliar directamente as pressões retrobulbares, impôem limitações sobre a interpretação de fluxos e pressões arteriais e venosas. Por fim, e dado a elevada prevalência de SVP em indivíduos saudáveis, ainda que com a maior série registada na literatura, o nosso reduzido número de individuos controlo sem SVP poderá levantar reservas sobre a significância estatística a atribuir aos nossos resultados nesta população. Concluindo, e ainda que seja necessário ainda complementar o nosso estudo com outros trabalhos incidindo nesta vertente de circulação venosa no glaucoma, o nosso trabalho parece demonstrar que as pulsatibilidades venosas poderão ser particularmente importantes nos doentes com NTG, onde a ausência das mesmas poderá sinalizar não só uma disfunção vascular (arterial e venosa) como também uma forma mais avançada da doença
Therapeutisch potentieel van VEGF en PlGF inhibitie in littekenvorming na glaucoom filtratie chirurgie
No full textGlaucoma is a neurodegenerative disease and the second most important cause of irreversible blindness. This disease is characterized by a raised intraocular pressure (IOP) and by progressive retinal ganglion cell degeneration, resulting in irreversible visual field loss. Filtration surgery (trabeculectomy) remains the most effective therapy to reduce IOP in glaucoma patients. However, in 30% of the cases this surgery fails due to subconjunctival wound healing. Pharmacological enhancement of trabeculectomy using different anti-scarring agents was found to significantly improve rates of surgical success. However, the nonspecific mechanism of action of these agents may result in severe side-effects. Therefore, there is still a need for alternative strategies to prevent filtration failure. Vascular endothelial growth factor (VEGF) plays an important role in both physiological and pathological angiogenesis. VEGF-R2 mediates most biologically relevant VEGF responses, including vascular permeability, cell migration and proliferation. Alternative splicing of a single VEGF-gene results in multiple isoforms, such as VEGF121, VEGF165 and VEGF189. Different anti-VEGF treatments are used in the ophthalmological practice, some of which have more selective properties. Pegaptanib (Macugen, Pfizer) is an aptamer that selectively prevents the binding of VEGF165 to its receptor, whereas bevacizumab (AvastinTM; Genentech) is a humanized, monoclonal full-length antibody against all isoforms. Placental growth factor (PlGF) is a VEGF-homologue which only binds to VEGF-R1. Therefore, this growth factor only acts on pathological angiogenesis and inflammation and is not involved in physiological angiogenic processes. A monoclonal anti-PlGF antibody against mouse PlGF-2 was developed by ThromboGenics NV. In this thesis work, we explored the hypothesis that VEGF and PlGF are playing an important role in scar formation after glaucoma filtration surgery and that they may be targets for improvement of filtration surgery outcome. The exact role of the different VEGF isoforms in the process of wound healing was also studied. The effect of non-selective and selective VEGF inhibitors and inhibition of PlGF on ocular wound healing was investigated in vivo using different animal models of glaucoma filtration surgery. In the first part of this thesis, we demonstrated that VEGF and PlGF are important players in scar formation in vitro. Aqeuous humor of glaucoma patients was collected and aqueous levels of VEGF and PlGF were significantly upregulated compared to control (cataract). Tenon fibroblasts (TF) and endothelial cells, both regarded as key players in wound healing after glaucoma surgery, were cultured and the expression of VEGF, PlGF and their receptors was determined. Quantitative real-time RT-PCR showed that both growth factors and their receptors (VEGF-R1 and VEGF-R2) were indeed expressed on these cells. Moreover, VEGF and PlGF were able to significantly stimulate proliferation of Tenon fibroblasts.  In a second chapter, we showed that the different VEGF isoforms were differentially involved in ocular wound healing. We demonstrated that VEGF121 and VEGF165 significantly stimulated proliferation of endothelial cells, by activating the ERK pathway. PD98059, an inhibitor of the ERK pathway, significantly inhibited VEGF121 and VEGF165-induced endothelial cell proliferation. We also reported the effect of the different isoforms on TF growth. We showed that TF proliferation was mainly induced by VEGF121 and VEGF189, associated with an activation of the ERK pathway. These proliferative effects were significantly reduced by the ERK pathway inhibitor PD98059. Thus, our results indicated that VEGF isoforms play a differential role not only in ocular angiogenesis but also in wound healing. VEGF165 was found to be the most important isoform in inducing endothelial cell proliferation, while VEGF189 was the most prominent in inducing TF proliferation. VEGF121 clearly affected both cell types. In a third section, the therapeutic potential of selective versus non-selective VEGF inhibition (pegaptanib versus bevacizumab) was investigated in vitro and in vivo by analyzing the area and survival of the filtration bleb area and process of wound healing of rabbit eyes following surgery. Proliferation assays on endothelial cells and TF suggested that non-selective VEGF inhibition might be anti-angiogenic and anti-fibrotic, while selective VEGF165 blockage might mainly inhibit angiogenesis. Indeed, these results were confirmed in our rabbit model for glaucoma surgery. A single administration of bevacizumab at the time of trabeculectomy could improve the surgical outcome by reducing postoperative angiogenesis during the initial phase, and collagen deposition at later stages. Pegaptanib injection(s) improved surgery outcome less efficiently by reducing angiogenesis only. Thus, our in vitro and in vivo data indicated that selective VEGF165 inhibition by pegaptanib was less effective than non-selective VEGF inhibition by bevacizumab in reducing scarring after glaucoma surgery, presumably due to retained action of VEGF121 and VEGF189 isoforms, which had a more pronounced effect on the Tenon fibroblasts as compared to VEGF165. Finally, in the last part, the therapeutic potential of PlGF inhibition was investigated. We showed that anti-VEGF therapy prevented post-surgical scarring by inhibiting angiogenesis and collagen deposition, but did not influence inflammation. Therefore, in collaboration with ThromboGenics NV, the known anti-angiogenic and anti-inflammatory, and possibly anti-fibrotic properties of anti-PlGF-antibody were studied in vitro and in vivo in a mouse model of glaucoma surgery. Administration of anti-PlGF antibody could reduce proliferation of TF in vitro and could improve the surgical outcome in vivo. Postoperative inflammation and angiogenesis was reduced during the initial phase and collagen deposition at later time points. Direct comparison showed that inhibition of PlGF possibly seemed to be even more effectively than inhibition of VEGF-R2, which only had an effect on angiogenesis and fibrosis. In conclusion, we showed that VEGF and PLGF are playing an important role in the process of wound healing after glaucoma surgery. Our study also sheds new light on the differential function of the VEGF isoforms in the mechanisms of angiogenesis and wound healing. VEGF165 and VEGF121 predominantly affect blood vessel growth, whereas VEGF189 seems to be more important in fibrosis. These insights may have important therapeutic implications for glaucoma patients. VEGF treatment - particularly non-selective - could improve the surgical outcome in glaucoma patients by reducing angiogenesis and fibrosis. On the other hand, inhibition of PlGF seems effective in improving surgical outcome by reducing inflammation, angiogenesis and collagen deposition. The insights generated within this thesis may open new perspectives not only for glaucoma surgery, but also for modulation of postoperative scarring in general.status: Publishe
Hou glaucoom patiënten in het oog: Patient gerapporteerde outcomes, therapietrouw met oogdruppelbehandeling en oogdruppelvaardigheden
No full textGlaucoma is a chronic disease in ophthalmology, affecting 3% of the Belgian population. The most important risk-factor of glaucoma is an elevated intraocular pressure. Objective outcomes such as visual field and optic nerve defects only give limited information about the real impact of glaucoma and its treatment on a patients daily life. Therefore the patients perspective or so-called patient reported outcomes (PROs) are essential for evaluating treatment efficacy, clinical outcomes, and disease impact. Due to the treatment complexity, its lifelong character and the presumable effect of nonadherence on disease outcomes, nonadherence should be considered as a very important PRO for patients with glaucoma. Yet, the PRO and adherence literature in glaucoma is characterized by content-and methodology related shortcomings. To fill these gaps, we first performed a systematic review on glaucoma specific PROs and rated them on their quality (chapter 2). Second, a prospective study was conducted to explore the dynamics of eye drop nonadherence and its theory based predictors (chapter 3). Third, we investigated selected system factors in relation to nonadherence in a multi-center study (chapter 4). Fourth, we developed and validated instruments to assess two important theoretical drivers of nonadherence, i.e. barriers (chapter 5) and eye drop administration skills (chapter 6). Patient reported outcomes (PROs) in glaucomaOf the 25 PRO-tools retrieved from literature, most were quality of life measures, with most being poorly developed and not validated according to the current methodological standards. A conceptual definition/framework and patient input were often lacking, which is mandatory for the guidance of the item generation process and further psychometric testing. Second, the selection of items in the final instrument and dimensionality was seldom tested using appropriate statistical techniques, while this is needed to derive subsequent valid (sub) scale scores. Third, the widely applied one size fits all rating scale is outdated, meaning that rating scales should be statistically justified with ranges that might vary across items and within 1 instrument. Finally, researchers should first provide strong evidence with respect to the instruments content validity, before starting further validation based on predefined hypotheses. Unfortunately, most tools did not meet these requirements, indicating a need for well developed and validated PRO instruments for use in glaucoma populations. Future directions in PRO-research should be: 1) improving existing instruments using Rasch-analysis, 2) developing and validating new PROs using modern validation techniques and 3) creating glaucoma specific item banks per patient reported outcome content (e.g. quality of life, side effects, adherence) integrating calibrated scales adapted to the patients ability.Nonadherence to eye drop treatmentIn our prospective study the prevalence of eye drop nonadherence was 52% at baseline and 68.4% after follow-up. Repeated measurements allowed us to detect 4 medication behavior dynamics, i.e. stable adherence, persistent nonadherence, increasing and decreasing adherence, learning us that 25% of the patients altered their behavior over time. Most of the patients reported more problems with timing- (i.e. about 40-47%) compared to taking nonadherence (or instilling eye drops) (i.e. about 30%)). Future studies hence should prospectively monitor adherence over time. Due to possible effects of timing deviations on the effectiveness of eye drops, attention should not only be given to instilling eye drops (i.e. taking adherence), but also to keeping regular intervals between doses (i.e. timing adherence). At patient-level, the number of reported barriers was the single significant predictor of eye drop nonadherence. Other factors such as knowledge, eye drop administration skills, and intention do not seem to play a major role in predicting medication adherence based on the Integrated Model of Behavioral Prediction we used to operationalize our risk factors of interest. Hence, assessing barriers and subsequently developing adherence-enhancing interventions are necessary to prevent adherence. Unfortunately, the glaucoma literature did not provide a well developed and validated tool to assess these barriers. We therefore developed a 13-item instrument focusing on barriers to eye drop adherence. The median number of reported barriers by glaucoma patients was 2 barriers (range 2-10), with the most frequently reported barriers being I had difficulties with getting an eye drop into my eye, something interfered with my daily routine (e.g. vacation) and I forgot to administer my eye drops. Given that barriers are highly individually determined, tailored interventions are mandatory. Besides risk-factors at the patient level, policy guidelines recommend that factors at the healthcare provider and healthcare system are worthwhile to be looked at. In our cross-sectional, multicenter study, using multilevel analyses, we found that, on top of known determinants at the patient level, patients with a lower frequency of follow-up (< every 3 months) are at higher risk for nonadherence, compared to patients visiting their ophthalmologist less frequently. This study also revealed that ophthalmologists cannot accurately detect nonadherence, given that the sensitivity of their adherence-assessment against self-report was only 3%. This indicates the need for training of ophthalmologists in adherence measurement. Not only is the high prevalence of eye drop nonadherence a concern, yet patients also seemed to possess poor eye drop administration skills. These findings were congruent with previous results, yet our study was the first to assess these skills using a standardized observation tool (EYEDO) we developed based on the state of the art eye drop administration technique based on the Fraunfelder method and American Academy of Ophthalmology guidelines. By using an objective observation scale, problems inherent to self-report (i.e. social desirability) are eliminated. When usingthe EyeDO in a sample of 133 patients with glaucoma, the most problematic skills were: 1) forming a conjunctival pocket (20.5%), 2) directing the bottle properly above the eye (60.6%) and 3) compressing the lachrymal duct for 1 to 3 minutes (85.6%). ConclusionGlaucoma demands many self management tasks of patients, which should be supported by the health care team. Based on our results, patients are preferably seen at least every 3 months during their life-long follow-up. Moreover, there is a need to educate and train both patients and professionals in adherence and eye drop administration skills. An advanced practice nurse can play a crucial role in bridging the gap between research and clinical practice. Not only can she support the team by giving evidence based education and training, but can also strengthen patients self management skills. More specifically, an advanced practice nurse can assess adherence and barriers to adherence regularly throughout long-term follow-up and offer patient-tailored interventions to overcome these barriers. Yet, these interventions have to be tested on their efficacy and effectiveness in future studies.status: Publishe
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