Real-world outcomes in patients with neovascular age-related macular degeneration treated with intravitreal vascular endothelial growth factor inhibitors Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2018-01-02 Hemal Mehta, Adnan Tufail, Vincent Daien, Aaron Lee, Vuong Nguyen, Mehmet Ozturk, Daniel Barthelmes, Mark C. Gillies
Clinical trials identified intravitreal vascular endothelial growth factor inhibitors (anti-VEGF agents) have the potential to stabilise or even improve visual acuity outcomes in neovascular age-related macular degeneration (AMD), a sight-threatening disease. Real-world evidence allows us to assess whether results from randomised controlled trials can be applied to the general population. We describe the development of global registries, in particular the Fight Retinal Blindness! registry that originated in Australia, the United Kingdom AMD Electronic Medical Records User Group and the IRIS registry in the USA. Real-world observations relating to efficacy, safety and resource utilisation of intravitreal anti-VEGF therapy for neovascular AMD are then summarised. Novel observations that would have been challenging to identify in a clinical trial setting are then highlighted, including the risk of late disease reactivation, outcomes in second versus first treated eyes, and the increased risk of posterior capsular rupture during cataract surgery in patients who have received intravitreal anti-VEGF therapy. We conclude by exploring future directions in the field. This includes the development of a global consensus on real-world outcome measures to allow greater comparison of results. Real-world neovascular AMD outcome registries can be linked with other databases to determine systemic safety or genetic predictors of treatment efficacy. Machine learning offers opportunities to extract useful insights from “Big Data” often collected in these registries. Real-world registries could be used by drug regulatory authorities and industry as an alternative to more costly and time-consuming phase 4 clinical trials, potentially allowing medication costs to be based on outcomes achieved.
Optical coherence tomography angiography Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-12-08 Richard F. Spaide, James G. Fujimoto, Nadia K. Waheed, Srinivas R. Sadda, Giovanni Staurenghi
Optical coherence tomography (OCT) was one of the biggest advances in ophthalmic imaging. Building on that platform, OCT angiography (OCTA) provides depth resolved images of blood flow in the retina and choroid with levels of detailed far exceeding that obtained with older forms of imaging. This new modality is challenging because of the need for new equipment and processing techniques, current limitations of imaging capability, and rapid advancements in both imaging and in our understanding of the imaging and applicable pathophysiology of the retina and choroid, and the requirement for understanding the origins of image artifacts. These factors lead to a steep learning curve, even for those with a working understanding dye-based ocular angiography. All for a method of imaging that is a little more than 10 years old. This review begins with a historical account of the development of OCTA, and the methods used in OCTA, including signal processing, image generation, and display techniques. This forms the basis to understand what OCTA images show as well as how image artifacts arise. The anatomy and imaging of specific vascular layers of the eye are reviewed. The integration of OCTA in multimodal imaging in the evaluation of retinal vascular occlusive diseases, diabetic retinopathy, uveitis, inherited diseases, age-related macular degeneration, and disorders of the optic nerve is presented. OCTA is an exciting, disruptive technology. Its use is rapidly expanding in clinical practice as well as for research into the pathophysiology of diseases of the posterior pole.
Neural control of choroidal blood flow Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-12-08 Anton Reiner, Malinda E.C. Fitzgerald, Nobel Del Mar, Chunyan Li
The choroid is richly innervated by parasympathetic, sympathetic and trigeminal sensory nerve fibers that regulate choroidal blood flow in birds and mammals, and presumably other vertebrate classes as well. The parasympathetic innervation has been shown to vasodilate and increase choroidal blood flow, the sympathetic input has been shown to vasoconstrict and decrease choroidal blood flow, and the sensory input has been shown to both convey pain and thermal information centrally and act locally to vasodilate and increase choroidal blood flow. As the choroid lies behind the retina and cannot respond readily to retinal metabolic signals, its innervation is important for adjustments in flow required by either retinal activity, by fluctuations in the systemic blood pressure driving choroidal perfusion, and possibly by retinal temperature. The former two appear to be mediated by the sympathetic and parasympathetic nervous systems, via central circuits responsive to retinal activity and systemic blood pressure, but adjustments for ocular perfusion pressure also appear to be influenced by local autoregulatory myogenic mechanisms. Adaptive choroidal responses to temperature may be mediated by trigeminal sensory fibers. Impairments in the neural control of choroidal blood flow occur with aging, and various ocular or systemic diseases such as glaucoma, age-related macular degeneration (AMD), hypertension, and diabetes, and may contribute to retinal pathology and dysfunction in these conditions, or in the case of AMD be a precondition. The present manuscript reviews findings in birds and mammals that contribute to the above-summarized understanding of the roles of the autonomic and sensory innervation of the choroid in controlling choroidal blood flow, and in the importance of such regulation for maintaining retinal health.
Towards the application of precision medicine in age-related Macular Degeneration Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-11-29 Raffaella Cascella, Claudia Strafella, Valerio Caputo, Valeria Errichiello, Stefania Zampatti, Filippo Milano, Saverio Potenza, Silvestro Mauriello, Giuseppe Novelli, Federico Ricci, Andrea Cusumano, Emiliano Giardina
The review essentially describes genetic and non-genetic variables contributing to the onset and progression of exudative Age-related Macular Degeneration (AMD) in Italian population. In particular, AMD susceptibility within Italian population is contributed to by genetic variants, accounting for 23% of disease and non-genetic variants, accounting for 10% of AMD. Our data highlighted prominent differences concerning genetic and non-genetic contributors to AMD in our cohort with respect to worldwide populations. Among genetic variables, SNPs of CFH, ARMS2, IL-8, TIMP3, SLC16A8, RAD51B, VEGFA and COL8A1 were significantly associated with the risk of AMD in the Italian cohort. Surprisingly, other susceptibility variants described in European, American and Asiatic populations, did not reach the significance threshold in our cohort. As expected, advanced age, smoking and dietary habits were associated with the disease. In addition, we also describe a number of gene-gene and gene-phenotype interactions. In fact, AMD-associated genes may be involved in the alteration of Bruch's membrane and induction of angiogenesis, contributing to exacerbate the damage caused by aging and environmental factors. Our review provides an overview of genetic and non-genetic factors characterizing AMD susceptibility in Italian population, outlining the differences with respect to the worldwide populations. Altogether, these data reflect historical, geographic, demographic and lifestyle peculiarities of Italian population. The role of epigenetics, pharmacogenetics, comorbities and genetic counseling in the management of AMD patients have been described, in the perspective of the application of a “population-specific precision medicine” approach addressed to prevent AMD onset and improve patients’ quality of life.
Retinal vasculature development in health and disease Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-11-10 Senthil Selvam, Tejas Kumar, Marcus Fruttiger
Development of the retinal vasculature is based on highly coordinated signalling between different cell types of the retina, integrating internal metabolic requirements with external influences such as the supply of oxygen and nutrients. The developing mouse retinal vasculature is a useful model system to study these interactions because it is experimentally accessible for intra ocular injections and genetic manipulations, can be easily imaged and develops in a similar fashion to that of humans. Research using this model has provided insights about general principles of angiogenesis as well as pathologies that affect the developing retinal vasculature. In this review, we discuss recent advances in our understanding of the molecular and cellular mechanisms that govern the interactions between neurons, glial and vascular cells in the developing retina. This includes a review of vascular mechanisms that shape the retinal vasculature, such as sprouting angiogenesis, vascular network remodelling and vessel maturation. We also explore how the disruption of these processes in mice can lead to pathology - such as oxygen induced retinopathy - and how this translates to human retinopathy of prematurity.
Mechanisms of macular edema: Beyond the surface Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-11-07 Alejandra Daruich, Alexandre Matet, Alexandre Moulin, Laura Kowalczuk, Michaël Nicolas, Alexandre Sellam, Pierre-Raphaël Rothschild, Samy Omri, Emmanuelle Gélizé, Laurent Jonet, Kimberley Delaunay, Yvonne De Kozak, Marianne Berdugo, Min Zhao, Patricia Crisanti, Francine Behar-Cohen
Macular edema consists of intra- or subretinal fluid accumulation in the macular region. It occurs during the course of numerous retinal disorders and can cause severe impairment of central vision. Major causes of macular edema include diabetes, branch and central retinal vein occlusion, choroidal neovascularization, posterior uveitis, postoperative inflammation and central serous chorioretinopathy. The healthy retina is maintained in a relatively dehydrated, transparent state compatible with optimal light transmission by multiple active and passive systems. Fluid accumulation results from an imbalance between processes governing fluid entry and exit, and is driven by Starling equation when inner or outer blood-retinal barriers are disrupted. The multiple and intricate mechanisms involved in retinal hydro-ionic homeostasis, their molecular and cellular basis, and how their deregulation lead to retinal edema, are addressed in this review. Analyzing the distribution of junction proteins and water channels in the human macula, several hypotheses are raised to explain why edema forms specifically in the macular region. “Pure” clinical phenotypes of macular edema, that result presumably from a single causative mechanism, are detailed. Finally, diabetic macular edema is investigated, as a complex multifactorial pathogenic example. This comprehensive review on the current understanding of macular edema and its mechanisms opens perspectives to identify new preventive and therapeutic strategies for this sight-threatening condition.
Development of the hyaloid, choroidal and retinal vasculatures in the fetal human eye Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-11-02 Gerard A. Lutty, D. Scott McLeod
The development of the ocular vasculatures is perfectly synchronized to provide the nutritional and oxygen requirements of the forming human eye. The fetal vasculature of vitreous, which includes the hyaloid vasculature, vasa hyaloidea propria, and tunica vasculosa lentis, initially develops around 4–6 weeks gestation (WG) by hemo-vasculogenesis (development of blood and blood vessels from a common progenitor, the hemangioblast). This transient fetal vasculature expands around 12 WG by angiogenesis (budding from primordial vessels) and remains until a retinal vasculature begins to form. The fetal vasculature then regresses by apoptosis with the assistance of macrophages/hyalocytes. The human choroidal vasculature also forms by a similar process and will supply nutrients and oxygen to outer retina. This lobular vasculature develops in a dense collagenous tissue juxtaposed with a cell constitutively producing vascular endothelial growth factor (VEGF), the retinal pigment epithelium. This epithelial/endothelial relationship is critical in maintaining the function of this vasculature throughout life and maintaining it's fenestrated state. The lobular capillary system (choriocapillaris) develops first by hemo-vasculogenesis and then the intermediate choroidal blood vessels form by angiogenesis, budding from the choriocapillaris. The human retinal vasculature is the last to develop. It develops by vasculogenesis, assembly of CXCR4+/CD39+ angioblasts or vascular progenitors perhaps using Muller cell Notch1 or axonal neuropilinin-1 for guidance of semaphorin 3A-expressing angioblasts. The fovea never develops a retinal vasculature, which is probably due to the foveal avascular zone area of retina expressing high levels of antiangiogenic factors. From these studies, it is apparent that development of the mouse ocular vasculatures is not representative of the development of the human fetal, choroidal and retinal vasculatures.
Molecular genetics and emerging therapies for retinitis pigmentosa: Basic research and clinical perspectives Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-10-31 Marina França Dias, Kwangsic Joo, Jessica A. Kemp, Silvia Ligório Fialho, Armando da Silva Cunha Jr., Se Joon Woo, Young Jik Kwon
Diagnosis and treatment guideline for myopic choroidal neovascularization due to pathologic myopia Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-10-28 Kyoko Ohno-Matsui, Yasushi Ikuno, Timothy Y.Y. Lai, Chui Ming Gemmy Cheung
Pathologic myopia is a leading cause of visual impairment. Development of myopic choroidal neovascularization (CNV) is one of the most common complications that leads to central vision loss in patients with pathologic myopia. If left untreated, it can cause scarring with expanding macular atrophy leading to irreversible visual loss in a period as short as 5 years. Advancements in multimodal imaging technology have furthered our understanding of the condition; however, further studies are necessary to extend its utility in the diagnosis of myopic CNV. Intravitreal anti-vascular endothelial growth factor (anti-VEGF) therapy has become the standard-of-care and the recommended first-line treatment option for myopic CNV. Long-term studies have demonstrated that early treatment of confirmed myopic CNV cases with an intravitreal anti-VEGF agent is useful to avoid late-stage complications. This strategy has also been shown to achieve visual outcome improvements for up to 4 years and visual stabilization up to 6 years. This review article provides an overview of the current knowledge on myopic CNV and discusses recent updates in the diagnosis and management of the condition. Furthermore, treatment recommendations are provided based on the authors’ expert opinions.
Genotype-functional-phenotype correlations in photoreceptor guanylate cyclase (GC-E) encoded by GUCY2D Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-10-20 Dror Sharon, Hanna Wimberg, Yael Kinarty, Karl-Wilhelm Koch
The GUCY2D gene encodes for the photoreceptor guanylate cyclase GC-E that synthesizes the intracellular messenger of photoreceptor excitation cGMP and is regulated by intracellular Ca2+-sensor proteins named guanylate cyclase-activating proteins (GCAPs). Over 140 disease-causing mutations have been described so far in GUCY2D, 88% of which cause autosomal recessive Leber congenital amaurosis (LCA) while heterozygous missense mutations cause autosomal dominant cone-rod degeneration (adCRD). Mutations in GUCY2D are one of the major causes of all LCA cases and are the major cause of adCRD. A single amino acid, arginine at position 838, is likely to be the most sensitive one in GC-E as four single mutations and two complex mutations were reported to affect R838.The biochemical effect of 45 GC-E variants was studied showing a clear genotype-phenotype correlation: LCA-causing mutations either show reduced ability or complete inability to synthesize cGMP from GTP, while CRD-causing mutations are functional, but shift the Ca2+-sensitivity of the GC-E – GCAP complex.Eight animal models of retinal guanylate cyclase deficiency have been reported including knockout (KO) mouse and chicken models. These two models were used for gene augmentation therapy that yielded promising results.Here we integrate the available information on the genetics, biochemistry and phenotype that is related to GUCY2D mutations. These data clearly show that mutation type (missense versus null) and localization (dimerization domain versus other protein domains) are correlated with the pattern of inheritance, impact on enzymatic function and retinal phenotype. Such clear correlation is unique to GUCY2D while mutations in many other retinal disease genes show variable phenotypes and lack of available biochemical assays.
The molecular and cellular basis of rhodopsin retinitis pigmentosa reveals potential strategies for therapy Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-10-16 Dimitra Athanasiou, Monica Aguila, James Bellingham, Wenwen Li, Caroline McCulley, Philip J. Reeves, Michael E. Cheetham
Inherited mutations in the rod visual pigment, rhodopsin, cause the degenerative blinding condition, retinitis pigmentosa (RP). Over 150 different mutations in rhodopsin have been identified and, collectively, they are the most common cause of autosomal dominant RP (adRP). Mutations in rhodopsin are also associated with dominant congenital stationary night blindness (adCSNB) and, less frequently, recessive RP (arRP). Recessive RP is usually associated with loss of rhodopsin function, whereas the dominant conditions are a consequence of gain of function and/or dominant negative activity. The in-depth characterisation of many rhodopsin mutations has revealed that there are distinct consequences on the protein structure and function associated with different mutations. Here we categorise rhodopsin mutations into seven discrete classes; with defects ranging from misfolding and disruption of proteostasis, through mislocalisation and disrupted intracellular traffic to instability and altered function. Rhodopsin adRP offers a unique paradigm to understand how disturbances in photoreceptor homeostasis can lead to neuronal cell death. Furthermore, a wide range of therapies have been tested in rhodopsin RP, from gene therapy and gene editing to pharmacological interventions. The understanding of the disease mechanisms associated with rhodopsin RP and the development of targeted therapies offer the potential of treatment for this currently untreatable neurodegeneration.
The mechanism of cone cell death in Retinitis Pigmentosa Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-09-27 Peter A. Campochiaro, Tahreem A. Mir
Retinitis Pigmentosa (RP) is a group of diseases in which one of a large number of mutations causes death of rod photoreceptors. After rods die, cone photoreceptors slowly degenerate in a characteristic pattern. The mechanism of rod cell death varies depending upon the gene that is mutated and the rate that rods degenerate is an important prognostic feature, because cones do not begin to degenerate until almost all rods have been eliminated. Rod cell death causes night blindness, but visual disability and blindness result from cone degeneration and therefore it is critical to determine the mechanisms by which it occurs. The death of rods reduces oxygen consumption resulting in high tissue levels of oxygen in the outer retina. The excess oxygen stimulates superoxide radical production by mismatches in the electron transport chain in mitochondria and by stimulation of NADPH oxidase activity in cytoplasm. The high levels of superoxide radicals overwhelm the antioxidant defense system and generate more reactive species including peroxynitrite which is extremely damaging and difficult to detoxify. This results in progressive oxidative damage in cones which contributes to cone cell death and loss of function because drugs or gene transfer that reduce oxidative stress promote cone survival and maintenance of function. Compared with aqueous humor samples from control patients, those from patients with RP show significant elevation of carbonyl content on proteins indicating oxidative damage and a reduction in the ratio of reduced to oxidized glutathione indicating depletion of a major component of the antioxidant defense system from ongoing oxidative stress. The first step in clinical trials will be to identify doses of therapeutic agents that reverse these biomarkers of disease to assist in design of much longer trials with functional and anatomic endpoints.
Pathophysiology, screening and treatment of ROP: A multi-disciplinary perspective Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-09-27 Tailoi Chan-Ling, Glen A. Gole, Graham E. Quinn, Samuel J. Adamson, Brian A. Darlow
The population of infants at risk for retinopathy of prematurity (ROP) varies by world region; in countries with well developed neonatal intensive care services, the highest risk infants are those born at less than 28 weeks gestational age (GA) and less than 1 kg at birth, while, in regions where many aspects of neonatal intensive and ophthalmological care are not routinely available, more mature infants up to 2000 g at birth and 37 weeks GA are also at risk for severe ROP. Treatment options for both groups of patients include standard retinal laser photocoagulation or, more recently, intravitreal anti-VEGF drugs. In addition to detection and treatment of ROP, this review highlights new opportunities created by telemedicine, where screening and diagnosis of ROP in remote locations can be undertaken by non-ophthalmologists using digital fundus cameras. The ophthalmological care of the ROP infant is undertaken in the wider context of neonatal care and general wellbeing of the infant. Because of this context, this review takes a multi-disciplinary perspective with contributions from retinal vascular biologists, pediatric ophthalmologists, an epidemiologist and a neonatologist. This review highlights the latest insights regarding cellular and molecular mechanisms in the formation of the retinal vasculature in the human infant, pathogenesis of ROP, detection and treatment of severe ROP, the risks and benefits of anti-VEGF therapy, the identification of new therapies over the horizon, and the optimal neonatal care regimen for best ROP outcomes, and the benefits and pitfalls of telemedicine in the remote screening and diagnosis of ROP, all of which have the potential to improve ROP outcomes.
The epidemics of myopia: Aetiology and prevention Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-09-23 Ian G. Morgan, Amanda N. French, Regan S. Ashby, Xinxing Guo, Xiaohu Ding, Mingguang He, Kathryn A. Rose
There is an epidemic of myopia in East and Southeast Asia, with the prevalence of myopia in young adults around 80–90%, and an accompanying high prevalence of high myopia in young adults (10–20%). This may foreshadow an increase in low vision and blindness due to pathological myopia. These two epidemics are linked, since the increasingly early onset of myopia, combined with high progression rates, naturally generates an epidemic of high myopia, with high prevalences of “acquired” high myopia appearing around the age of 11–13. The major risk factors identified are intensive education, and limited time outdoors. The localization of the epidemic appears to be due to the high educational pressures and limited time outdoors in the region, rather than to genetically elevated sensitivity to these factors. Causality has been demonstrated in the case of time outdoors through randomized clinical trials in which increased time outdoors in schools has prevented the onset of myopia. In the case of educational pressures, evidence of causality comes from the high prevalence of myopia and high myopia in Jewish boys attending Orthodox schools in Israel compared to their sisters attending religious schools, and boys and girls attending secular schools. Combining increased time outdoors in schools, to slow the onset of myopia, with clinical methods for slowing myopic progression, should lead to the control of this epidemic, which would otherwise pose a major health challenge. Reforms to the organization of school systems to reduce intense early competition for accelerated learning pathways may also be important.
Manipulating ocular endothelial tight junctions: Applications in treatment of retinal disease pathology and ocular hypertension Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-09-22 Matthew Campbell, Paul S. Cassidy, Jeffrey O'Callaghan, Darragh E. Crosbie, Pete Humphries
Protein levels of endothelial tight-junctions of the inner retinal microvasculature, together with those of Schlemm's canal, can be readily manipulated by RNA interference (RNAi), resulting in the paracellular clefts between such cells to be reversibly modulated. This facilitates access to the retina of systemically-deliverable low molecular weight, potentially therapeutic compounds, while also allowing potentially toxic material, for example, soluble Amyloid-β1-40, to be removed from the retina into the peripheral circulation. The technique has also been shown to be highly effective in alleviation of pathological cerebral oedema and we speculate that it may therefore have similar utility in the oedematous retina. Additionally, by manipulating endothelial tight-junctions of Schlemm's canal, inflow of aqueous humour from the trabecular meshwork into the Canal can be radically enhanced, suggesting a novel avenue for control of intraocular pressure. Here, we review the technology underlying this approach together with specific examples of clinical targets that are, or could be, amenable to this novel form of genetic intervention.
Complement factor H in AMD: Bridging genetic associations and pathobiology Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-09-18 Christopher B. Toomey, Lincoln V. Johnson, Catherine Bowes Rickman
AMD is a complex multifactorial disease characterized in its early stages by lipoprotein accumulations in BrM, seen on fundoscopic exam as drusen, and in its late forms by neovascularization (“wet”) or geographic atrophy of the RPE cell layer (“dry”). Genetic studies have strongly supported a relationship between the alternative complement cascade, in particular the common H402 variant in Complement Factor H (CFH) and development of AMD. However, the functional significance of the CFH Y402H polymorphism remains elusive. In this article, we critically review the literature surrounding the functional significance of this polymorphism. Furthermore, based on our group's studies we propose a model in which CFH H402 affects CFH binding to heparan sulfate proteoglycans leading to accelerated lipoprotein accumulation in BrM and drusen progression. We also review the literature on the role of other complement components in AMD pathobiologies, including C3a, C5a and membrane attack complex (MAC) and on transgenic mouse models developed to interrogate in vivo the effects of the CFH H402 polymorphism.
Age-related cataracts: Role of unfolded protein response, Ca2+ mobilization, epigenetic DNA modifications, and loss of Nrf2/Keap1 dependent cytoprotection Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-08-31 Palsamy Periyasamy, Toshimichi Shinohara
Age-related cataracts are closely associated with lens chronological aging, oxidation, calcium imbalance, hydration and crystallin modifications. Accumulating evidence indicates that misfolded proteins are generated in the endoplasmic reticulum (ER) by most cataractogenic stresses. To eliminate misfolded proteins from cells before they can induce senescence, the cells activate a clean-up machinery called the ER stress/unfolded protein response (UPR). The UPR also activates the nuclear factor-erythroid-2-related factor 2 (Nrf2), a central transcriptional factor for cytoprotection against stress. Nrf2 activates nearly 600 cytoprotective target genes. However, if ER stress reaches critically high levels, the UPR activates destructive outputs to trigger programmed cell death. The UPR activates mobilization of ER-Ca2+ to the cytoplasm and results in activation of Ca2+-dependent proteases to cleave various enzymes and proteins which cause the loss of normal lens function. The UPR also enhances the overproduction of reactive oxygen species (ROS), which damage lens constituents and induce failure of the Nrf2 dependent cytoprotection. Kelch-like ECH-associated protein 1 (Keap1) is an oxygen sensor protein and regulates the levels of Nrf2 by the proteasomal degradation. A significant loss of DNA methylation in diabetic cataracts was found in the Keap1 promoter, which overexpresses the Keap1 protein. Overexpressed Keap1 significantly decreases the levels of Nrf2. Lower levels of Nrf2 induces loss of the redox balance toward to oxidative stress thereby leading to failure of lens cytoprotection. Here, this review summarizes the overall view of ER stress, increases in Ca2+ levels, protein cleavage, and loss of the well-established stress protection in somatic lens cells.
A novel hypothesis for the pathogenesis of glaucomatous disc hemorrhage Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-08-30 Eun Jung Lee, Jong Chul Han, Changwon Kee
Disc hemorrhage is known to be associated with glaucoma development and progression. Several hypotheses have been proposed to explain the pathogenesis of disc hemorrhage in glaucoma, including mechanical and ischemic theories. However, no theory has yet provided a clear explanation of cellular-level events and related histologic findings. Moreover, research has yet to elucidate why glaucomatous disc hemorrhage occurs around the optic disc and at the margin of the retinal nerve fiber layer defect. Understanding the pathogenic mechanism of disc hemorrhage will facilitate interpretation of its clinical importance, and provide better insight into clinical practice. In this review, we sought to provide a plausible hypothesis for the development of glaucomatous disc hemorrhage that could explain the aforementioned characteristic features. We suggest a new and detailed mechanism for disc hemorrhage. Critical microscopic events are also discussed in relation to reactive gliosis in glaucoma. With proliferative reactive gliosis, fibrous glial scar forms, and we suggest that the traction force induced by glial scar formation might disrupt capillary at the border between the healthy and damaged retinal nerve fiber layer, and develop splinter-shaped peripapillary hemorrhage. In addition to glial scar formation, remodeling and deformation of lamina cribrosa beams would insult the capillary surrounding the pore of the lamina cribrosa, and lead to development of round blotch-shaped cup hemorrhage. Histopathologic confirmation of these findings should be explored in future investigations.
Myofibroblast transdifferentiation: The dark force in ocular wound healing and fibrosis Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-08-12 Daisy Y. Shu, Frank J. Lovicu
Wound healing is one of the most complex biological processes to occur in life. Repair of tissue following injury involves dynamic interactions between multiple cell types, growth factors, inflammatory mediators and components of the extracellular matrix (ECM). Aberrant and uncontrolled wound healing leads to a non-functional mass of fibrotic tissue. In the eye, fibrotic disease disrupts the normally transparent ocular tissues resulting in irreversible loss of vision. A common feature in fibrotic eye disease is the transdifferentiation of cells into myofibroblasts that can occur through a process known as epithelial-mesenchymal transition (EMT). Myofibroblasts rapidly produce excessive amounts of ECM and exert tractional forces across the ECM, resulting in the distortion of tissue architecture. Transforming growth factor-beta (TGFβ) plays a major role in myofibroblast transdifferentiation and has been implicated in numerous fibrotic eye diseases including corneal opacification, pterygium, anterior subcapsular cataract, posterior capsular opacification, proliferative vitreoretinopathy, fibrovascular membrane formation associated with proliferative diabetic retinopathy, submacular fibrosis, glaucoma and orbital fibrosis. This review serves to introduce the pathological functions of the myofibroblast in fibrotic eye disease. We also highlight recent developments in elucidating the multiple signaling pathways involved in fibrogenesis that may be exploited in the development of novel anti-fibrotic therapies to reduce ocular morbidity due to scarring.
Optical coherence tomography angiography: A comprehensive review of current methods and clinical applications Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-07-29 Amir H. Kashani, Chieh-Li Chen, Jin K. Gahm, Fang Zheng, Grace M. Richter, Philip J. Rosenfeld, Yonggang Shi, Ruikang K. Wang
OCT has revolutionized the practice of ophthalmology over the past 10–20 years. Advances in OCT technology have allowed for the creation of novel OCT-based methods. OCT-Angiography (OCTA) is one such method that has rapidly gained clinical acceptance since it was approved by the FDA in late 2016. OCTA images are based on the variable backscattering of light from the vascular and neurosensory tissue in the retina. Since the intensity and phase of backscattered light from retinal tissue varies based on the intrinsic movement of the tissue (e.g. red blood cells are moving, but neurosensory tissue is static), OCTA images are essentially motion-contrast images. This motion-contrast imaging provides reliable, high resolution, and non-invasive images of the retinal vasculature in an efficient manner. In many cases, these images are approaching histology level resolution. This unprecedented resolution coupled with the simple, fast and non-invasive imaging platform have allowed a host of basic and clinical research applications. OCTA demonstrates many important clinical findings including areas of macular telangiectasia, impaired perfusion, microaneurysms, capillary remodeling, some types of intraretinal fluid, and neovascularization among many others. More importantly, OCTA provides depth-resolved information that has never before been available. Correspondingly, OCTA has been used to evaluate a spectrum of retinal vascular diseases including diabetic retinopathy (DR), retinal venous occlusion (RVO), uveitis, retinal arterial occlusion, and age-related macular degeneration among others. In this review, we will discuss the methods used to create OCTA images, the practical applications of OCTA in light of invasive dye-imaging studies (e.g. fluorescein angiography) and review clinical studies demonstrating the utility of OCTA for research and clinical practice.
Phosphenes, retinal discrete dark noise, negative afterimages and retinogeniculate projections: A new explanatory framework based on endogenous ocular luminescence Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-07-17 Vahid Salari, Felix Scholkmann, Ram Lakhan Pandey Vimal, Noémi Császár, Mehdi Aslani, István Bókkon
Cellular luminescence is the emission of photons by living cells due to various biophysical and biochemical processes, mostly associated with cellular metabolism. In this review paper we summarize today's understanding of four luminescence-dependent phenomena in the eye, i.e., phosphenes, retinal discrete dark noise, negative afterimages and the development of retinogeniculate projections in the brain. We review the phenomena above in the context of knowledge gained from experimental and theoretical works. Finally, we discuss this knowledge in terms of its physiological significance.
The connective tissue phenotype of glaucomatous cupping in the monkey eye - Clinical and research implications Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-03-12 Hongli Yang, Juan Reynaud, Howard Lockwood, Galen Williams, Christy Hardin, Luke Reyes, Cheri Stowell, Stuart K. Gardiner, Claude F. Burgoyne
In a series of previous publications we have proposed a framework for conceptualizing the optic nerve head (ONH) as a biomechanical structure. That framework proposes important roles for intraocular pressure (IOP), IOP-related stress and strain, cerebrospinal fluid pressure (CSFp), systemic and ocular determinants of blood flow, inflammation, auto-immunity, genetics, and other non-IOP related risk factors in the physiology of ONH aging and the pathophysiology of glaucomatous damage to the ONH. The present report summarizes 20 years of technique development and study results pertinent to the characterization of ONH connective tissue deformation and remodeling in the unilateral monkey experimental glaucoma (EG) model. In it we propose that the defining pathophysiology of a glaucomatous optic neuropathy involves deformation, remodeling, and mechanical failure of the ONH connective tissues. We view this as an active process, driven by astrocyte, microglial, fibroblast and oligodendrocyte mechanobiology. These cells, and the connective tissue phenomena they propagate, have primary and secondary effects on retinal ganglion cell (RGC) axon, laminar beam and retrolaminar capillary homeostasis that may initially be “protective” but eventually lead to RGC axonal injury, repair and/or cell death. The primary goal of this report is to summarize our 3D histomorphometric and optical coherence tomography (OCT)-based evidence for the early onset and progression of ONH connective tissue deformation and remodeling in monkey EG. A second goal is to explain the importance of including ONH connective tissue processes in characterizing the phenotype of a glaucomatous optic neuropathy in all species. A third goal is to summarize our current efforts to move from ONH morphology to the cell biology of connective tissue remodeling and axonal insult early in the disease. A final goal is to facilitate the translation of our findings and ideas into neuroprotective interventions that target these ONH phenomena for therapeutic effect.
Unravelling the genetics of inherited retinal dystrophies: Past, present and future Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-03-29 Suzanne Broadgate, Jing Yu, Susan M. Downes, Stephanie Halford
The identification of the genes underlying monogenic diseases has been of interest to clinicians and scientists for many years. Using inherited retinal dystrophies as an example of monogenic disease we describe the history of molecular genetic techniques that have been pivotal in the discovery of disease causing genes. The methods that were developed in the 1970's and 80's are still in use today but have been refined and improved. These techniques enabled the concept of the Human Genome Project to be envisaged and ultimately realised. When the successful conclusion of the project was announced in 2003 many new tools and, as importantly, many collaborations had been developed that facilitated a rapid identification of disease genes. In the post-human genome project era advances in computing power and the clever use of the properties of DNA replication has allowed the development of next-generation sequencing technologies. These methods have revolutionised the identification of disease genes because for the first time there is no need to define the position of the gene in the genome. The use of next generation sequencing in a diagnostic setting has allowed many more patients with an inherited retinal dystrophy to obtain a molecular diagnosis for their disease. The identification of novel genes that have a role in the development or maintenance of retinal function is opening up avenues of research which will lead to the development of new pharmacological and gene therapy approaches. Neither of which can be used unless the defective gene and protein is known. The continued development of sequencing technologies also holds great promise for the advent of truly personalised medicine.
Alternatives to eye bank native tissue for corneal stromal replacement Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-04-24 Isabelle Brunette, Cynthia J. Roberts, François Vidal, Mona Harissi-Dagher, Jean Lachaine, Heather Sheardown, Georges M. Durr, Stéphanie Proulx, May Griffith
Corneal blindness is a major cause of blindness in the world and corneal transplantation is the only widely accepted treatment to restore sight in these eyes. However, it is becoming increasingly difficult for eye banks to meet the increasing demand for transplantable tissue, which is in part due to population aging. Donor tissue shortage is therefore a growing concern globally and there is a need for alternatives to human donor corneas. Biosynthetic corneal substitutes offer several significant advantages over native corneas: Large-scale production offers a powerful potential solution to the severe shortage of human donor corneas worldwide; Good manufacturing practices ensure sterility and quality control; Acellular corneal substitutes circumvent immune rejection induced by allogeneic cells; Optical and biomechanical properties of the implants can be adapted to the clinical need; and finally these corneal substitutes could benefit from new advances in biomaterials science, such as surface coating, functionalization and nanoparticles. This review highlights critical contributions from laboratories working on corneal stromal substitutes. It focuses on synthetic inert prostheses (keratoprostheses), acellular scaffolds with and without enhancement of endogenous regeneration, and cell-based replacements. Accent is put on the physical properties and biocompatibility of these biomaterials, on the functional and clinical outcome once transplanted in vivo in animal or human eyes, as well as on the main challenges of corneal stromal replacement. Regulatory and economic aspects are also discussed. All of these perspectives combined highlight the founding principles of the clinical application of corneal stromal replacement, a concept that has now become reality.
Lateral thinking – Interocular symmetry and asymmetry in neurovascular patterning, in health and disease Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-04-28 James R. Cameron, Roly D. Megaw, Andrew J. Tatham, Sarah McGrory, Thomas J. MacGillivray, Fergus N. Doubal, Joanna M. Wardlaw, Emanuele Trucco, Siddharthan Chandran, Baljean Dhillon
No biological system or structure is likely to be perfectly symmetrical, or have identical right and left forms. This review explores the evidence for eye and visual pathway asymmetry, in health and in disease, and attempts to provide guidance for those studying the structure and function of the visual system, where recognition of symmetry or asymmetry may be essential.The principal question with regards to asymmetry is not ‘are the eyes the same?’, for some degree of asymmetry is pervasive, but ‘when are they importantly different?’. Knowing if right and left eyes are ‘importantly different’ could have significant consequences for deciding whether right or left eyes are included in an analysis or for examining the association between a phenotype and ocular parameter. The presence of significant asymmetry would also have important implications for the design of normative databases of retinal and optic nerve metrics.In this review, we highlight not only the universal presence of asymmetry, but provide evidence that some elements of the visual system are inherently more asymmetric than others, pointing to the need for improved normative data to explain sources of asymmetry and their impact on determining associations with genetic, environmental or health-related factors and ultimately in clinical practice.
Roles of exosomes in the normal and diseased eye Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-04-29 Mikael Klingeborn, W. Michael Dismuke, Catherine Bowes Rickman, W. Daniel Stamer
Exosomes are nanometer-sized vesicles that are released by cells in a controlled fashion and mediate a plethora of extra- and intercellular activities. Some key functions of exosomes include cell-cell communication, immune modulation, extracellular matrix turnover, stem cell division/differentiation, neovascularization and cellular waste removal. While much is known about their role in cancer, exosome function in the many specialized tissues of the eye is just beginning to undergo rigorous study. Here we review current knowledge of exosome function in the visual system in the context of larger bodies of data from other fields, in both health and disease. Additionally, we discuss recent advances in the exosome field including use of exosomes as a therapeutic vehicle, exosomes as a source of biomarkers for disease, plus current standards for isolation and validation of exosome populations. Finally, we use this foundational information about exosomes in the eye as a platform to identify areas of opportunity for future research studies.
The application of optical coherence tomography angiography in uveitis and inflammatory eye diseases Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-04-29 Francesco Pichi, David Sarraf, Sruthi Arepalli, Careen Y. Lowder, Emmett T. Cunningham, Piergiorgio Neri, Thomas A. Albini, Vishali Gupta, Kimberly Baynes, Sunil K. Srivastava
Since its introduction in the early 1990s, optical coherence tomography (OCT) has evolved in resolution and technological advances, and in recent years its initial application of assessing the morphology of a tissue has been implemented by the study of its functional blood flow, through optical coherence tomography angiography (OCTA). This novel technique details capillary networks by comparing the amount of light returned from static and moving targets without the need for intravenous dye administration. While this imaging modality has been used for various ocular conditions, the application OCTA to uveitis conditions remains sparse.This review aims to establish the basis of OCTA and its current application to ocular inflammatory disorders, with an emphasis on monitoring progression and response to treatment, as well as predicting visual complications. In particular, this review explores the use of OCTA in iris vessel dilation seen in various forms of iritis, as a predictive factor for further episodes of inflammation. OCTA can also depict ischemia in the deep plexus layers of the retina and identify true choroicapillaris ischemia in cases of placoid diseases or masking of the indocyanine green dye, as in multiple evanescent white dot syndrome. In addition, OCTA can depict neovascularization in granulomatous disease of the retina or choroid not previously depicted with previous imaging methods. While OCTA provides several advancements in the imaging, management and prognosis of uveitis diseases, we emphasize that further studies are required to fully understand its application to these conditions.
Fluorescence lifetime imaging ophthalmoscopy Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-06-30 Chantal Dysli, Sebastian Wolf, Mikhail Y. Berezin, Lydia Sauer, Martin Hammer, Martin S. Zinkernagel
Imaging techniques based on retinal autofluorescence have found broad applications in ophthalmology because they are extremely sensitive and noninvasive. Conventional fundus autofluorescence imaging measures fluorescence intensity of endogenous retinal fluorophores. It mainly derives its signal from lipofuscin at the level of the retinal pigment epithelium. Fundus autofluorescence, however, can not only be characterized by the spatial distribution of the fluorescence intensity or emission spectrum, but also by a characteristic fluorescence lifetime function. The fluorescence lifetime is the average amount of time a fluorophore remains in the excited state following excitation. Fluorescence lifetime imaging ophthalmoscopy (FLIO) is an emerging imaging modality for in vivo measurement of lifetimes of endogenous retinal fluorophores. Recent reports in this field have contributed to our understanding of the pathophysiology of various macular and retinal diseases.Within this review, the basic concept of fluorescence lifetime imaging is provided. It includes technical background information and correlation with in vitro measurements of individual retinal metabolites. In a second part, clinical applications of fluorescence lifetime imaging and fluorescence lifetime features of selected retinal diseases such as Stargardt disease, age-related macular degeneration, choroideremia, central serous chorioretinopathy, macular holes, diabetic retinopathy, and retinal artery occlusion are discussed. Potential areas of use for fluorescence lifetime imaging ophthalmoscopy will be outlined at the end of this review.
The chick eye in vision research: An excellent model for the study of ocular disease Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-06-28 C. Ellis Wisely, Javed A. Sayed, Heather Tamez, Chris Zelinka, Mohamed H. Abdel-Rahman, Andy J. Fischer, Colleen M. Cebulla
The domestic chicken, Gallus gallus, serves as an excellent model for the study of a wide range of ocular diseases and conditions. The purpose of this manuscript is to outline some anatomic, physiologic, and genetic features of this organism as a robust animal model for vision research, particularly for modeling human retinal disease. Advantages include a sequenced genome, a large eye, relative ease of handling and maintenance, and ready availability. Relevant similarities and differences to humans are highlighted for ocular structures as well as for general physiologic processes. Current research applications for various ocular diseases and conditions, including ocular imaging with spectral domain optical coherence tomography, are discussed. Several genetic and non-genetic ocular disease models are outlined, including for pathologic myopia, keratoconus, glaucoma, retinal detachment, retinal degeneration, ocular albinism, and ocular tumors. Finally, the use of stem cell technology to study the repair of damaged tissues in the chick eye is discussed. Overall, the chick model provides opportunities for high-throughput translational studies to more effectively prevent or treat blinding ocular diseases.
Connexin channel and its role in diabetic retinopathy Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-06-08 Sayon Roy, Jean X. Jiang, An-Fei Li, Dongjoon Kim
Diabetic retinopathy is the leading cause of blindness in the working age population. Unfortunately, there is no cure for this devastating ocular complication. The early stage of diabetic retinopathy is characterized by the loss of various cell types in the retina, namely endothelial cells and pericytes. As the disease progresses, vascular leakage, a clinical hallmark of diabetic retinopathy, becomes evident and may eventually lead to diabetic macular edema, the most common cause of vision loss in diabetic retinopathy. Substantial evidence indicates that the disruption of connexin-mediated cellular communication plays a critical role in the pathogenesis of diabetic retinopathy. Yet, it is unclear how altered communication via connexin channel mediated cell-to-cell and cell-to-extracellular microenvironment is linked to the development of diabetic retinopathy. Recent observations suggest the possibility that connexin hemichannels may play a role in the pathogenesis of diabetic retinopathy by allowing communication between cells and the microenvironment. Interestingly, recent studies suggest that connexin channels may be involved in regulating retinal vascular permeability. These cellular events are coordinated at least in part via connexin-mediated intercellular communication and the maintenance of retinal vascular homeostasis. This review highlights the effect of high glucose and diabetic condition on connexin channels and their impact on the development of diabetic retinopathy.
On phagocytes and macular degeneration Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-06-07 Xavier Guillonneau, Chiara M. Eandi, Michel Paques, José-Alain Sahel, Przemyslaw Sapieha, Florian Sennlaub
Age related macular degeneration (AMD) is a complex multifactorial disease caused by the interplay of age and genetic and environmental risk factors. A common feature observed in early and both forms of late AMD is the breakdown of the physiologically immunosuppressive subretinal environment and the protracted accumulation of mononuclear phagocytes (MP). We here discuss the origin and nature of subretinal MPs, the mechanisms that lead to their accumulation, the inflammatory mediators they produce as well as the consequences of their chronic presence on photoreceptors, retinal pigment epithelium and choroid. Recent advances highlight how both genetic and environmental risk factors directly promote subretinal inflammation and tip the balance from a beneficial inflammation that helps control debris accumulation to detrimental chronic inflammation and destructive late AMD. Finally, we discuss how changes in life style or pharmacological intervention can help to break the vicious cycle of inflammation and degeneration, restore the immunosuppressive properties of the subretinal space, and reestablish homeostasis.
Dopamine signaling and myopia development: What are the key challenges Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-06-07 Xiangtian Zhou, Machelle T. Pardue, P. Michael Iuvone, Jia Qu
In the face of an “epidemic” increase in myopia over the last decades and myopia prevalence predicted to reach 2.5 billion people by the end of this decade, there is an urgent need to develop effective and safe therapeutic interventions to slow down this “myopia booming” and prevent myopia-related complications and vision loss. Dopamine (DA) is an important neurotransmitter in the retina and mediates diverse functions including retina development, visual signaling, and refractive development. Inspired by the convergence of epidemiological and animal studies in support of the inverse relationship between outdoor activity and risk of developing myopia and by the close biological relationship between light exposure and dopamine release/signaling, we felt it is timely and important to critically review the role of DA in myopia development. This review will revisit several key points of evidence for and against DA mediating light control of myopia: 1) the causal role of extracellular retinal DA levels, 2) the mechanism and action of dopamine D1 and D2 receptors and 3) the roles of cellular/circuit retinal pathways. We examine the experiments that show causation by altering DA, DA receptors and visual pathways using pharmacological, transgenic, or visual environment approaches. Furthermore, we critically evaluate the safety issues of a DA-based treatment strategy and some approaches to address these issues. The review identifies the key questions and challenges in translating basic knowledge on DA signaling and myopia from animal studies into effective pharmacological treatments for myopia in children.
Human antimicrobial peptides in ocular surface defense Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-06-03 Imran Mohammed, Dalia G. Said, Harminder S. Dua
Sight depends on the passage of light through the transparent cornea and being focused on the fovea. Its exposed position renders it vulnerable to microbial infection. The cornea has developed a wide array of defense mechanisms against infection, of which endogenous antimicrobial peptides (AMPs) are key. AMPs are essentially small molecular weight cationic peptides with a wide range of activity against virus, bacteria, fungi and parasites. Some proteins such as RNases and S100As are also included in this group. Several AMPs act synergistically allowing low expression of multiple AMPs to act efficiently. AMPs also have a range of non-microbicidal functions and serve as signaling molecules, immunomodulators; show anti-tumour activity, and influence vascularization and wound healing. Different toll-like receptors (TLR) have been implicated in the preferential induction of specific AMPs. A range of bacteria, including mycobacteria tuberculosis, viruses including herpes virus, fungi and parasites including acanthamoeba, that cause ocular infections have been shown to induce specific AMPs via TLR activation. Non-TLR mediated induction of AMP expression can occur and several molecules such as L-isoleucine, sodium butyrate, vitamin D3, phenylbutyrate, vasoactive intestinal peptide, and etinostat have been identified in this regard. Given the rising microbe resistance to antibiotics, the slow rate of development of new antibiotics and the limited access to effective antibiotics by patients living in the developing world, an ideal solution would be to find AMPs that are effective singly or in combination with each other or other antimicrobial proteins to reduce, if possible eliminate reliance on antibiotics alone.
The role of systemic and topical fatty acids for dry eye treatment Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-05-19 Stefano Barabino, Jutta Horwath-Winter, Elisabeth M. Messmer, Maurizio Rolando, Pasquale Aragona, Shigeru Kinoshita
Dry eye is a prevalent condition and one of the main reasons for patients to seek ophthalmic medical care. A low systemic level of omega fatty acids is a risk factor for dry eye disease (DED). There are two groups of essential fatty acids (EFAs): the omega-6 (n-6) family and the omega-3 (n-3) family. Humans evolved on a diet in which the n-6:n-3 ratio was approximately 1:1, however the current Western diet tends to be deficient in n-3 EFAs and this ratio is typically much higher (approaching 17:1). The metabolism of EFAs generates four new families of local acting mediators: lipoxins, resolvins, protectins, and maresins. These molecules have anti-inflammatory and pro-resolution properties. We present a critical overview of animal model studies and human clinical trials that have shown that dietary modification and oral supplementation could be complementary therapeutic strategies for the treatment of dry eye. Furthermore, we discuss preliminary results of the topical application of n-3 and n-6 EFAs because these molecules may act as natural anti-inflammatory agents with positive changes of the entire ocular surface system.
Cilia - The sensory antennae in the eye Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-05-11 Helen May-Simera, Kerstin Nagel-Wolfrum, Uwe Wolfrum
Cilia are hair-like projections found on almost all cells in the human body. Originally believed to function merely in motility, the function of solitary non-motile (primary) cilia was long overlooked. Recent research has demonstrated that primary cilia function as signalling hubs that sense environmental cues and are pivotal for organ development and function, tissue hoemoestasis, and maintenance of human health. Cilia share a common anatomy and their diverse functional features are achieved by evolutionarily conserved functional modules, organized into sub-compartments. Defects in these functional modules are responsible for a rapidly growing list of human diseases collectively termed ciliopathies. Ocular pathogenesis is common in virtually all classes of syndromic ciliopathies, and disruptions in cilia genes have been found to be causative in a growing number of non-syndromic retinal dystrophies.This review will address what is currently known about cilia contribution to visual function. We will focus on the molecular and cellular functions of ciliary proteins and their role in the photoreceptor sensory cilia and their visual phenotypes. We also highlight other ciliated cell types in tissues of the eye (e.g. lens, RPE and Müller glia cells) discussing their possible contribution to disease progression. Progress in basic research on the cilia function in the eye is paving the way for therapeutic options for retinal ciliopathies. In the final section we describe the latest advancements in gene therapy, read-through of non-sense mutations and stem cell therapy, all being adopted to treat cilia dysfunction in the retina.
Cell-based therapeutic strategies for replacement and preservation in retinal degenerative diseases Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-01-19 Melissa K. Jones, Bin Lu, Sergey Girman, Shaomei Wang
Cell-based therapeutics offer diverse options for treating retinal degenerative diseases, such as age-related macular degeneration (AMD) and retinitis pigmentosa (RP). AMD is characterized by both genetic and environmental risks factors, whereas RP is mainly a monogenic disorder. Though treatments exist for some patients with neovascular AMD, a majority of retinal degenerative patients have no effective therapeutics, thus indicating a need for universal therapies to target diverse patient populations. Two main cell-based mechanistic approaches are being tested in clinical trials. Replacement therapies utilize cell-derived retinal pigment epithelial (RPE) cells to supplant lost or defective host RPE cells. These cells are similar in morphology and function to native RPE cells and can potentially supplant the responsibilities of RPE in vivo. Preservation therapies utilize supportive cells to aid in visual function and photoreceptor preservation partially by neurotrophic mechanisms. The goal of preservation strategies is to halt or slow the progression of disease and maintain remaining visual function. A number of clinical trials are testing the safety of replacement and preservation cell therapies in patients; however, measures of efficacy will need to be further evaluated. In addition, a number of prevailing concerns with regards to the immune-related response, longevity, and functionality of the grafted cells will need to be addressed in future trials. This review will summarize the current status of cell-based preclinical and clinical studies with a focus on replacement and preservation strategies and the obstacles that remain regarding these types of treatments.
Advances in thickness measurements and dynamic visualization of the tear film using non-invasive optical approaches☆ Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-02-23 Yuqiang Bai, Jason J. Nichols
The thickness of tear film has been investigated under both invasive and non-invasive methods. While invasive methods are largely historical, more recent noninvasive methods are generally based on optical approaches that provide accurate, precise, and rapid measures. Optical microscopy, interferometry, and optical coherence tomography (OCT) have been developed to characterize the thickness of tear film or certain aspects of the tear film (e.g., the lipid layer). This review provides an in-depth overview on contemporary optical techniques used in studying the tear film, including both advantages and limitations of these approaches. It is anticipated that further developments of high-resolution OCT and other interferometric methods will enable a more accurate and precise measurement of the thickness of the tear film and its related dynamic properties.
Bestrophin 1 and retinal disease Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-01-30 Adiv A. Johnson, Karina E. Guziewicz, C. Justin Lee, Ravi C. Kalathur, Jose S. Pulido, Lihua Y. Marmorstein, Alan D. Marmorstein
Mutations in the gene BEST1 are causally associated with as many as five clinically distinct retinal degenerative diseases, which are collectively referred to as the “bestrophinopathies”. These five associated diseases are: Best vitelliform macular dystrophy, autosomal recessive bestrophinopathy, adult-onset vitelliform macular dystrophy, autosomal dominant vitreoretinochoroidopathy, and retinitis pigmentosa. The most common of these is Best vitelliform macular dystrophy. Bestrophin 1 (Best1), the protein encoded by the gene BEST1, has been the subject of a great deal of research since it was first identified nearly two decades ago. Today we know that Best1 functions as both a pentameric anion channel and a regulator of intracellular Ca2+ signaling. Best1 is an integral membrane protein which, within the eye, is uniquely expressed in the retinal pigment epithelium where it predominantly localizes to the basolateral plasma membrane. Within the brain, Best1 expression has been documented in both glial cells and astrocytes where it functions in both tonic GABA release and glutamate transport. The crystal structure of Best1 has revealed critical information about how Best1 functions as an ion channel and how Ca2+ regulates that function. Studies using animal models have led to critical insights into the physiological roles of Best1 and advances in stem cell technology have allowed for the development of patient-derived, “disease in a dish” models. In this article we review our knowledge of Best1 and discuss prospects for near-term clinical trials to test therapies for the bestrophinopathies, a currently incurable and untreatable set of diseases.
Bestrophinopathy: An RPE-photoreceptor interface disease Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-01-19 Karina E. Guziewicz, Divya Sinha, Néstor M. Gómez, Kathryn Zorych, Emily V. Dutrow, Anuradha Dhingra, Robert F. Mullins, Edwin M. Stone, David M. Gamm, Kathleen Boesze-Battaglia, Gustavo D. Aguirre
Characterizing the “POAGome”: A bioinformatics-driven approach to primary open-angle glaucoma Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-02-20 Ian D. Danford, Lana D. Verkuil, Daniel J. Choi, David W. Collins, Harini V. Gudiseva, Katherine E. Uyhazi, Marisa K. Lau, Levi N. Kanu, Gregory R. Grant, Venkata R.M. Chavali, Joan M. O'Brien
Primary open-angle glaucoma (POAG) is a genetically, physiologically, and phenotypically complex neurodegenerative disorder. This study addressed the expanding collection of genes associated with POAG, referred to as the “POAGome.” We used bioinformatics tools to perform an extensive, systematic literature search and compiled 542 genes with confirmed associations with POAG and its related phenotypes (normal tension glaucoma, ocular hypertension, juvenile open-angle glaucoma, and primary congenital glaucoma). The genes were classified according to their associated ocular tissues and phenotypes, and functional annotation and pathway analyses were subsequently performed. Our study reveals that no single molecular pathway can encompass the pathophysiology of POAG. The analyses suggested that inflammation and senescence may play pivotal roles in both the development and perpetuation of the retinal ganglion cell degeneration seen in POAG. The TGF-β signaling pathway was repeatedly implicated in our analyses, suggesting that it may be an important contributor to the manifestation of POAG in the anterior and posterior segments of the globe. We propose a molecular model of POAG revolving around TGF-β signaling, which incorporates the roles of inflammation and senescence in this disease. Finally, we highlight emerging molecular therapies that show promise for treating POAG.
Retinal oxygen: from animals to humans Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-01-18 Robert A. Linsenmeier, Hao F. Zhang
This article discusses retinal oxygenation and retinal metabolism by focusing on measurements made with two of the principal methods used to study O2 in the retina: measurements of PO2 with oxygen-sensitive microelectrodes in vivo in animals with a retinal circulation similar to that of humans, and oximetry, which can be used non-invasively in both animals and humans to measure O2 concentration in retinal vessels. Microelectrodes uniquely have high spatial resolution, allowing the mapping of PO2 in detail, and when combined with mathematical models of diffusion and consumption, they provide information about retinal metabolism. Mathematical models, grounded in experiments, can also be used to simulate situations that are not amenable to experimental study. New methods of oximetry, particularly photoacoustic ophthalmoscopy and visible light optical coherence tomography, provide depth-resolved methods that can separate signals from blood vessels and surrounding tissues, and can be combined with blood flow measures to determine metabolic rate. We discuss the effects on retinal oxygenation of illumination, hypoxia and hyperoxia, and describe retinal oxygenation in diabetes, retinal detachment, arterial occlusion, and macular degeneration. We explain how the metabolic measurements obtained from microelectrodes and imaging are different, and how they need to be brought together in the future. Finally, we argue for revisiting the clinical use of hyperoxia in ophthalmology, particularly in retinal arterial occlusions and retinal detachment, based on animal research and diffusion theory.
The lens growth process Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-04-11 Steven Bassnett, Hrvoje Šikić
The factors that regulate the size of organs to ensure that they fit within an organism are not well understood. A simple organ, the ocular lens serves as a useful model with which to tackle this problem. In many systems, considerable variance in the organ growth process is tolerable. This is almost certainly not the case in the lens, which in addition to fitting comfortably within the eyeball, must also be of the correct size and shape to focus light sharply onto the retina. Furthermore, the lens does not perform its optical function in isolation. Its growth, which continues throughout life, must therefore be coordinated with that of other tissues in the optical train. Here, we review the lens growth process in detail, from pioneering clinical investigations in the late nineteenth century to insights gleaned more recently in the course of cell and molecular studies. During embryonic development, the lens forms from an invagination of surface ectoderm. Consequently, the progenitor cell population is located at its surface and differentiated cells are confined to the interior. The interactions that regulate cell fate thus occur within the obligate ellipsoidal geometry of the lens. In this context, mathematical models are particularly appropriate tools with which to examine the growth process. In addition to identifying key growth determinants, such models constitute a framework for integrating cell biological and optical data, helping clarify the relationship between gene expression in the lens and image quality at the retinal plane.
The impact of oxidative stress and inflammation on RPE degeneration in non-neovascular AMD Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-03-20 Sayantan Datta, Marisol Cano, Katayoon Ebrahimi, Lei Wang, James T. Handa
The retinal pigment epithelium (RPE) is a highly specialized, unique epithelial cell that interacts with photoreceptors on its apical side and with Bruch's membrane and the choriocapillaris on its basal side. Due to vital functions that keep photoreceptors healthy, the RPE is essential for maintaining vision. With aging and the accumulated effects of environmental stresses, the RPE can become dysfunctional and die. This degeneration plays a central role in age-related macular degeneration (AMD) pathobiology, the leading cause of blindness among the elderly in western societies. Oxidative stress and inflammation have both physiological and potentially pathological roles in RPE degeneration. Given the central role of the RPE, this review will focus on the impact of oxidative stress and inflammation on the RPE with AMD pathobiology. Physiological sources of oxidative stress as well as unique sources from photo-oxidative stress, the phagocytosis of photoreceptor outer segments, and modifiable factors such as cigarette smoking and high fat diet ingestion that can convert oxidative stress into a pathological role, and the negative impact of impairing the cytoprotective roles of mitochondrial dynamics and the Nrf2 signaling system on RPE health in AMD will be discussed. Likewise, the response by the innate immune system to an inciting trigger, and the potential role of local RPE production of inflammation, as well as a potential role for damage by inflammation with chronicity if the inciting trigger is not neutralized, will be debated.
BAX to basics: How the BCL2 gene family controls the death of retinal ganglion cells Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-01-04 Margaret E. Maes, Cassandra L. Schlamp, Robert W. Nickells
Retinal ganglion cell (RGC) death is the principal consequence of injury to the optic nerve. For several decades, we have understood that the RGC death process was executed by apoptosis, suggesting that there may be ways to therapeutically intervene in this cell death program and provide a more direct treatment to the cells and tissues affected in diseases like glaucoma. A major part of this endeavor has been to elucidate the molecular biological pathways active in RGCs from the point of axonal injury to the point of irreversible cell death. A major component of this process is the complex interaction of members of the BCL2 gene family. Three distinct family members of proteins orchestrate the most critical junction in the apoptotic program of RGCs, culminating in the activation of pro-apoptotic BAX. Once active, BAX causes irreparable damage to mitochondria, while precipitating downstream events that finish off a dying ganglion cell. This review is divided into two major parts. First, we summarize the extent of knowledge of how BCL2 gene family proteins interact to facilitate the activation and function of BAX. This area of investigation has rapidly changed over the last few years and has yielded a dramatically different mechanistic understanding of how the intrinsic apoptotic program is run in mammalian cells. Second, we provided a comprehensive analysis of nearly two decades of investigation of the role of BAX in the process of RGC death, much of which has provided many important insights into the overall pathophysiology of diseases like glaucoma.
Primary angle closure glaucoma: What we know and what we don’t know Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2016-12-28 Xinghuai Sun, Yi Dai, Yuhong Chen, Dao-Yi Yu, Stephen J. Cringle, Junyi Chen, Xiangmei Kong, Xiaolei Wang, Chunhui Jiang
Primary angle-closure glaucoma (PACG) is a common cause of blindness. Angle closure is a fundamental pathologic process in PAGC. With the development of imaging devices for the anterior segment of the eye, a better understanding of the pathogenesis of angle closure has been reached. Aside from pupillary block and plateau iris, multiple-mechanisms are more common contributors for closure of the angle such as choroidal thickness and uveal expansion, which may be responsible for the presenting features of PACG. Recent Genome Wide Association Studies identified several new PACG loci and genes, which may shed light on the molecular mechanisms of PACG. The current classification systems of PACG remain controversial. Focusing the anterior chamber angle is a principal management strategy for PACG. Treatments to open the angle or halt the angle closure process such as laser peripheral iridotomy and/or iridoplasty, as well as cataract extraction, are proving their effectiveness. PACG may be preventable in the early stages if future research can identify which kind of angles and/or persons are more likely to benefit from prophylactic treatment. New treatment strategies like adjusting the psychological status and balancing the sympathetic-parasympathetic nerve activity, and innovative medicines are needed to improve the prognosis of PACG.In this review, we intend to describe current understanding and unknown aspects of PACG, and to share the clinical experience and viewpoints of the authors.
Improving our understanding, and detection, of glaucomatous damage: An approach based upon optical coherence tomography (OCT) Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2016-12-22 Donald C. Hood
Although ophthalmologists are becoming increasingly reliant upon optical coherence tomography (OCT), clinicians who care for glaucoma patients are not taking full advantage of the potential of this powerful technology. First, we ask, how would one describe the nature of glaucomatous damage if only OCT scans were available? In particular, a schematic model of glaucomatous damage is developed in section 2, and the nature of glaucomatous damage seen on OCT scans described in the context of this model in section 3. In particular, we illustrate that local thinning of the circumpapillary retinal nerve fiber layer (cpRNFL) around the optic disc can vary in location, depth, and/or width, as well as homogeneity of damage. Second, we seek to better understand the relationship between the thinning of the cpRNFL and the various patterns of sensitivity loss seen on visual fields obtained with standard automated perimetry. In sections 4 and 5, we illustrate why one should expect a wide range of visual field patterns, and iilustrate why they should not be placed into discrete categories. Finally, section 6 describes how the clinician can take better advantage of the information in OCT scans. The approach is summarized in a single-page report, which can be generated from a single wide-field scan. The superiority of this approach, as opposed to the typical reliance on summary metrics, is described.
Adaptive optics optical coherence tomography in glaucoma Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2016-12-01 Zachary M. Dong, Gadi Wollstein, Bo Wang, Joel S. Schuman
Since the introduction of commercial optical coherence tomography (OCT) systems, the ophthalmic imaging modality has rapidly expanded and it has since changed the paradigm of visualization of the retina and revolutionized the management and diagnosis of neuro-retinal diseases, including glaucoma. OCT remains a dynamic and evolving imaging modality, growing from time-domain OCT to the improved spectral-domain OCT, adapting novel image analysis and processing methods, and onto the newer swept-source OCT and the implementation of adaptive optics (AO) into OCT. The incorporation of AO into ophthalmic imaging modalities has enhanced OCT by improving image resolution and quality, particularly in the posterior segment of the eye. Although OCT previously captured in-vivo cross-sectional images with unparalleled high resolution in the axial direction, monochromatic aberrations of the eye limit transverse or lateral resolution to about 15–20 μm and reduce overall image quality. In pairing AO technology with OCT, it is now possible to obtain diffraction-limited resolution images of the optic nerve head and retina in three-dimensions, increasing resolution down to a theoretical 3 μm3. It is now possible to visualize discrete structures within the posterior eye, such as photoreceptors, retinal nerve fiber layer bundles, the lamina cribrosa, and other structures relevant to glaucoma. Despite its limitations and barriers to widespread commercialization, the expanding role of AO in OCT is propelling this technology into clinical trials and onto becoming an invaluable modality in the clinician's arsenal.
Imaging retina to study dementia and stroke Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2017-01-03 Carol Yim-lui Cheung, M. Kamran Ikram, Christopher Chen, Tien Yin Wong
With increase in life expectancy, the number of persons suffering from common age-related brain diseases, including neurodegenerative (e.g., dementia) and cerebrovascular (e.g., stroke) disease is expected to rise substantially. As current neuro-imaging modalities such as magnetic resonance imaging may not be able to detect subtle subclinical changes (resolution <100–500 μm) in dementia and stroke, there is an urgent need for other complementary techniques to probe the pathophysiology of these diseases. The retina - due to its anatomical, embryological and physiological similarities with the brain - offers a unique and accessible “window” to study correlates and consequences of subclinical pathology in the brain. Retinal components such as the microvasculature and retinal ganglion cell axons can now be visualized non-invasively using different retinal imaging techniques e.g., ocular fundus photography and optical coherence tomography. Advances in retinal imaging may provide new and potentially important insights into cerebrovascular neurodegenerative processes in addition to what is currently possible with neuro-imaging. In this review, we present an overview of the current literature on the application of retinal imaging in the study of dementia and stroke. We discuss clinical implications of these studies, novel state-of-the-art retinal imaging techniques and future directions aimed at evaluating whether retinal imaging can be an additional investigation tool in the study of dementia and stroke.
Aqueous outflow - A continuum from trabecular meshwork to episcleral veins Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2016-12-24 Teresia Carreon, Elizabeth van der Merwe, Ronald L. Fellman, Murray Johnstone, Sanjoy K. Bhattacharya
In glaucoma, lowered intraocular pressure (IOP) confers neuroprotection. Elevated IOP characterizes glaucoma and arises from impaired aqueous humor (AH) outflow. Increased resistance in the trabecular meshwork (TM), a filter-like structure essential to regulate AH outflow, may result in the impaired outflow. Flow through the 360° circumference of TM structures may be non-uniform, divided into high and low flow regions, termed as segmental. After flowing through the TM, AH enters Schlemm's canal (SC), which expresses both blood and lymphatic markers; AH then passes into collector channel entrances (CCE) along the SC external well. From the CCE, AH enters a deep scleral plexus (DSP) of vessels that typically run parallel to SC. From the DSP, intrascleral collector vessels run radially to the scleral surface to connect with AH containing vessels called aqueous veins to discharge AH to blood-containing episcleral veins. However, the molecular mechanisms that maintain homeostatic properties of endothelial cells along the pathways are not well understood. How these molecular events change during aging and in glaucoma pathology remain unresolved. In this review, we propose mechanistic possibilities to explain the continuum of AH outflow control, which originates at the TM and extends through collector channels to the episcleral veins.
Pharmacokinetic aspects of retinal drug delivery Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2016-12-24 Eva M. del Amo, Anna-Kaisa Rimpelä, Emma Heikkinen, Otto K. Kari, Eva Ramsay, Tatu Lajunen, Mechthild Schmitt, Laura Pelkonen, Madhushree Bhattacharya, Dominique Richardson, Astrid Subrizi, Tiina Turunen, Mika Reinisalo, Jaakko Itkonen, Elisa Toropainen, Marco Casteleijn, Heidi Kidron, Maxim Antopolsky, Arto Urtti
Drug delivery to the posterior eye segment is an important challenge in ophthalmology, because many diseases affect the retina and choroid leading to impaired vision or blindness. Currently, intravitreal injections are the method of choice to administer drugs to the retina, but this approach is applicable only in selected cases (e.g. anti-VEGF antibodies and soluble receptors). There are two basic approaches that can be adopted to improve retinal drug delivery: prolonged and/or retina targeted delivery of intravitreal drugs and use of other routes of drug administration, such as periocular, suprachoroidal, sub-retinal, systemic, or topical. Properties of the administration route, drug and delivery system determine the efficacy and safety of these approaches. Pharmacokinetic and pharmacodynamic factors determine the required dosing rates and doses that are needed for drug action. In addition, tolerability factors limit the use of many materials in ocular drug delivery. This review article provides a critical discussion of retinal drug delivery, particularly from the pharmacokinetic point of view. This article does not include an extensive review of drug delivery technologies, because they have already been reviewed several times recently. Instead, we aim to provide a systematic and quantitative view on the pharmacokinetic factors in drug delivery to the posterior eye segment. This review is based on the literature and unpublished data from the authors' laboratory.
In vivo genome editing as a potential treatment strategy for inherited retinal dystrophies Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2016-09-10 Mert Yanik, Brigitte Müller, Fei Song, Jacqueline Gall, Franziska Wagner, Wolfgang Wende, Birgit Lorenz, Knut Stieger
In vivo genome editing represents an emerging field in the treatment of monogenic disorders, as it may constitute a solution to the current hurdles in classic gene addition therapy, which are the low levels and limited duration of transgene expression. Following the introduction of a double strand break (DSB) at the mutational site by highly specific endonucleases, such as TALENs (transcription activator like effector nucleases) or RNA based nucleases (clustered regulatory interspaced short palindromic repeats - CRISPR-Cas), the cell's own DNA repair machinery restores integrity to the DNA strand and corrects the mutant sequence, thus allowing the cell to produce protein levels as needed. The DNA repair happens either through the error prone non-homologous end-joining (NHEJ) pathway or with high fidelity through homology directed repair (HDR) in the presence of a DNA donor template. A third pathway called microhomology mediated endjoining (MMEJ) has been recently discovered. In this review, the authors focus on the different DNA repair mechanisms, the current state of the art tools for genome editing and the particularities of the retina and photoreceptors with regard to in vivo therapeutic approaches. Finally, current attempts in the field of retinal in vivo genome editing are discussed and future directions of research identified.
Retinal regeneration mechanisms linked to multiple cancer molecules: A therapeutic conundrum Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2016-08-30 Amanda Barber, Kyle Farmer, Keith R. Martin, Patrice D. Smith
Over the last decade, a large number of research articles have been published demonstrating regeneration and/or neuroprotection of retinal ganglion cells following manipulation of specific genetic and molecular targets. Interestingly, of the targets that have been identified to promote repair following visual system damage, many are genes known to be mutated in different types of cancer. This review explores recent literature on the potential for modulating cancer genes as a therapeutic strategy for visual system repair and looks at the potential clinical challenges associated with implementing this type of therapy. We also discuss signalling mechanisms that have been implicated in cancer and consider how similar mechanisms may improve axonal regeneration in the optic nerve.
The neural retina in retinopathy of prematurity Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2016-09-23 Ronald M. Hansen, Anne Moskowitz, James D. Akula, Anne B. Fulton
Retinopathy of prematurity (ROP) is a neurovascular disease that affects prematurely born infants and is known to have significant long term effects on vision. We conducted the studies described herein not only to learn more about vision but also about the pathogenesis of ROP. The coincidence of ROP onset and rapid developmental elongation of the rod photoreceptor outer segments motivated us to consider the role of the rods in this disease. We used noninvasive electroretinographic (ERG), psychophysical, and retinal imaging procedures to study the function and structure of the neurosensory retina. Rod photoreceptor and post-receptor responses are significantly altered years after the preterm days during which ROP is an active disease. The alterations include persistent rod dysfunction, and evidence of compensatory remodeling of the post-receptor retina is found in ERG responses to full-field stimuli and in psychophysical thresholds that probe small retinal regions. In the central retina, both Mild and Severe ROP delay maturation of parafoveal scotopic thresholds and are associated with attenuation of cone mediated multifocal ERG responses, significant thickening of post-receptor retinal laminae, and dysmorphic cone photoreceptors. These results have implications for vision and control of eye growth and refractive development and suggest future research directions. These results also lead to a proposal for noninvasive management using light that may add to the currently invasive therapeutic armamentarium against ROP.
Steroid-induced ocular hypertension/glaucoma: Focus on pharmacogenomics and implications for precision medicine Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2016-09-22 M. Elizabeth Fini, Stephen G. Schwartz, Xiaoyi Gao, Shinwu Jeong, Nitin Patel, Tatsuo Itakura, Marianne O. Price, Francis W. Price Jr., Rohit Varma, W. Daniel Stamer
Elevation of intraocular pressure (IOP) due to therapeutic use of glucocorticoids is called steroid-induced ocular hypertension (SIOH); this can lead to steroid-induced glaucoma (SIG). Glucocorticoids initiate signaling cascades ultimately affecting expression of hundreds of genes; this provides the potential for a highly personalized pharmacological response. Studies attempting to define genetic risk factors were undertaken early in the history of glucocorticoid use, however scientific tools available at that time were limited and progress stalled. In contrast, significant advances were made over the ensuing years in defining disease pathophysiology. As the genomics age emerged, it appeared the time was right to renew investigation into genetics. Pharmacogenomics is an unbiased discovery approach, not requiring an underlying hypothesis, and provides a way to pinpoint clinically significant genes and pathways that could not have been discovered any other way. Results of the first genome-wide association study to identify polymorphisms associated with SIOH, and follow-up on two novel genes linked to the disorder, GPR158 and HCG22, is discussed in the second half of the article. However, knowledge of genetic variants determining response to steroids in the eye also has value in its own right as a predictive and diagnostic tool. This article concludes with a discussion of how the Precision Medicine Initiative®, announced by U.S. President Obama in his 2015 State of the Union address, is beginning to touch the practice of ophthalmology. It is argued that SIOH/SIG may provide one of the next opportunities for effective application of precision medicine.
The physiological optics of the lens Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2016-09-14 Paul J. Donaldson, Angus C. Grey, Bianca Maceo Heilman, Julie C. Lim, Ehsan Vaghefi
The optical properties of the ocular lens are important to overall vision quality. As a transparent biological tissue, the lens contributes to the overall and dynamic focussing power of the eye, and corrects for optical errors introduced by the cornea. The optical properties of the lens change throughout life. Alterations to the refractive properties and transparency of the lens result in presbyopia and cataract, respectively. However, it is not well understood how changes to lens cellular structure and function initiate these changes in refraction and transparency. Here, we attempt to bridge this knowledge gap by reviewing how the optical properties of the lens are first established, and then maintained at the cellular level throughout the lifetime of an individual. Central to this understanding is the fact that the lens has a microcirculation system that generates a flux of ions and water that circulates through the lens. By supporting ionic and metabolic homeostasis in the lens, the system actively maintains lens transparency, and by regulating the steady state water content of the lens, controls the two key parameters, lens geometry and the gradient of refractive index, which determine the refractive properties of the lens. Thus, water transport is emerging as the critical parameter that links the transparency and refractive properties of the lens at the cellular level, and highlights the need to study how age-related changes in water transport result in presbyopia and cataract, the leading causes of refractive error and blindness in the world today.
Caveolins and caveolae in ocular physiology and pathophysiology Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2016-09-21 Xiaowu Gu, Alaina M. Reagan, Mark E. McClellan, Michael H. Elliott
Caveolae are specialized, invaginated plasma membrane domains that are defined morphologically and by the expression of signature proteins called, caveolins. Caveolae and caveolins are abundant in a variety of cell types including vascular endothelium, glia, and fibroblasts where they play critical roles in transcellular transport, endocytosis, mechanotransduction, cell proliferation, membrane lipid homeostasis, and signal transduction. Given these critical cellular functions, it is surprising that ablation of the caveolae organelle does not result in lethality suggesting instead that caveolae and caveolins play modulatory roles in cellular homeostasis. Caveolar components are also expressed in ocular cell types including retinal vascular cells, Müller glia, retinal pigment epithelium (RPE), conventional aqueous humor outflow cells, the corneal epithelium and endothelium, and the lens epithelium. In the eye, studies of caveolae and other membrane microdomains (i.e., “lipid rafts”) have lagged behind what is a substantial body of literature outside vision science. However, interest in caveolae and their molecular components has increased with accumulating evidence of important roles in vision-related functions such as blood-retinal barrier homeostasis, ocular inflammatory signaling, pathogen entry at the ocular surface, and aqueous humor drainage. The recent association of CAV1/2 gene loci with primary open angle glaucoma and intraocular pressure has further enhanced the need to better understand caveolar functions in the context of ocular physiology and disease. Herein, we provide the first comprehensive review of literature on caveolae, caveolins, and other membrane domains in the context of visual system function. This review highlights the importance of caveolae domains and their components in ocular physiology and pathophysiology and emphasizes the need to better understand these important modulators of cellular function.
Detection and measurement of clinically meaningful visual field progression in clinical trials for glaucoma Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2016-10-20 C. Gustavo De Moraes, Jeffrey M. Liebmann, Leonard A. Levin
Glaucomatous visual field progression has both personal and societal costs and therefore has a serious impact on quality of life. At the present time, intraocular pressure (IOP) is considered to be the most important modifiable risk factor for glaucoma onset and progression. Reduction of IOP has been repeatedly demonstrated to be an effective intervention across the spectrum of glaucoma, regardless of subtype or disease stage. In the setting of approval of IOP-lowering therapies, it is expected that effects on IOP will translate into benefits in long-term patient-reported outcomes. Nonetheless, the effect of these medications on IOP and their associated risks can be consistently and objectively measured. This helps to explain why regulatory approval of new therapies in glaucoma has historically used IOP as the outcome variable. Although all approved treatments for glaucoma involve IOP reduction, patients frequently continue to progress despite treatment. It would therefore be beneficial to develop treatments that preserve visual function through mechanisms other than lowering IOP. The United States Food and Drug Administration (FDA) has stated that they will accept a clinically meaningful definition of visual field progression using Glaucoma Change Probability criteria. Nonetheless, these criteria do not take into account the time (and hence, the speed) needed to reach significant change. In this paper we provide an analysis based on the existing literature to support the hypothesis that decreasing the rate of visual field progression by 30% in a trial lasting 12–18 months is clinically meaningful. We demonstrate that a 30% decrease in rate of visual field progression can be reliably projected to have a significant effect on health-related quality of life, as defined by validated instruments designed to measure that endpoint.
Advances in bone marrow stem cell therapy for retinal dysfunction Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2016-10-23 Susanna S. Park, Elad Moisseiev, Gerhard Bauer, Johnathon D. Anderson, Maria B. Grant, Azhar Zam, Robert J. Zawadzki, John S. Werner, Jan A. Nolta
The most common cause of untreatable vision loss is dysfunction of the retina. Conditions, such as age-related macular degeneration, diabetic retinopathy and glaucoma remain leading causes of untreatable blindness worldwide. Various stem cell approaches are being explored for treatment of retinal regeneration. The rationale for using bone marrow stem cells to treat retinal dysfunction is based on preclinical evidence showing that bone marrow stem cells can rescue degenerating and ischemic retina. These stem cells have primarily paracrine trophic effects although some cells can directly incorporate into damaged tissue. Since the paracrine trophic effects can have regenerative effects on multiple cells in the retina, the use of this cell therapy is not limited to a particular retinal condition. Autologous bone marrow-derived stem cells are being explored in early clinical trials as therapy for various retinal conditions. These bone marrow stem cells include mesenchymal stem cells, mononuclear cells and CD34+ cells. Autologous therapy requires no systemic immunosuppression or donor matching. Intravitreal delivery of CD34+ cells and mononuclear cells appears to be tolerated and is being explored since some of these cells can home into the damaged retina after intravitreal administration. The safety of intravitreal delivery of mesenchymal stem cells has not been well established. This review provides an update of the current evidence in support of the use of bone marrow stem cells as treatment for retinal dysfunction. The potential limitations and complications of using certain forms of bone marrow stem cells as therapy are discussed. Future directions of research include methods to optimize the therapeutic potential of these stem cells, non-cellular alternatives using extracellular vesicles, and in vivo high-resolution retinal imaging to detect cellular changes in the retina following cell therapy.
Next generation sequencing technology and genomewide data analysis: Perspectives for retinal research Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2016-06-11 Vijender Chaitankar, Gökhan Karakülah, Rinki Ratnapriya, Felipe O. Giuste, Matthew J. Brooks, Anand Swaroop
The advent of high throughput next generation sequencing (NGS) has accelerated the pace of discovery of disease-associated genetic variants and genomewide profiling of expressed sequences and epigenetic marks, thereby permitting systems-based analyses of ocular development and disease. Rapid evolution of NGS and associated methodologies presents significant challenges in acquisition, management, and analysis of large data sets and for extracting biologically or clinically relevant information. Here we illustrate the basic design of commonly used NGS-based methods, specifically whole exome sequencing, transcriptome, and epigenome profiling, and provide recommendations for data analyses. We briefly discuss systems biology approaches for integrating multiple data sets to elucidate gene regulatory or disease networks. While we provide examples from the retina, the NGS guidelines reviewed here are applicable to other tissues/cell types as well.
Structural and molecular bases of rod photoreceptor morphogenesis and disease Prog. Retin. Eye. Res. (IF 11.587) Pub Date : 2016-06-22 Theodore G. Wensel, Zhixian Zhang, Ivan A. Anastassov, Jared C. Gilliam, Feng He, Michael F. Schmid, Michael A. Robichaux
The rod cell has an extraordinarily specialized structure that allows it to carry out its unique function of detecting individual photons of light. Both the structural features of the rod and the metabolic processes required for highly amplified light detection seem to have rendered the rod especially sensitive to structural and metabolic defects, so that a large number of gene defects are primarily associated with rod cell death and give rise to blinding retinal dystrophies. The structures of the rod, especially those of the sensory cilium known as the outer segment, have been the subject of structural, biochemical, and genetic analysis for many years, but the molecular bases for rod morphogenesis and for cell death in rod dystrophies are still poorly understood. Recent developments in imaging technology, such as cryo-electron tomography and super-resolution fluorescence microscopy, in gene sequencing technology, and in gene editing technology are rapidly leading to new breakthroughs in our understanding of these questions. A summary is presented of our current understanding of selected aspects of these questions, highlighting areas of uncertainty and contention as well as recent discoveries that provide new insights. Examples of structural data from emerging imaging technologies are presented.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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