- •Diabetic Retinopathy
- •Preface
- •Contents
- •Contributors
- •Nonproliferative Diabetic Retinopathy
- •Nonproliferative Diabetic Retinopathy
- •Inflammatory Mechanisms
- •Microaneurysms
- •Vascular Permeability
- •Capillary Closure
- •Classification Of Nonproliferative Retinopathy
- •Macular Edema
- •Risk Factors For Progression Of Retinopathy
- •Severity of Retinopathy
- •Glycemic Control
- •The Diabetes Control and Complications Trial
- •Epidemiology of Diabetes Interventions and Complications Trial
- •The United Kingdom Prospective Diabetes Study
- •Hypertension
- •The United Kingdom Prospective Diabetes Study
- •Appropriate Blood Pressure Control in Diabetes Trials
- •Elevated Serum Lipid Levels
- •Pregnancy and Diabetic Retinopathy
- •Other Systemic Risk Factors
- •Management Of Nonproliferative Diabetic Retinopathy
- •Photocoagulation
- •Scatter Photocoagulation for Nonproliferative Diabetic Retinopathy
- •Scatter Photocoagulation for Proliferative Retinopathy
- •Focal Photocoagulation for Diabetic Macular Edema
- •Other Treatment of Diabetic Macular Edema
- •Medical Therapy
- •Aspirin And Antiplatelet Treatments
- •Aldose Reductase Inhibitors
- •Other Medical Treatments
- •Summary
- •Acknowledgment
- •References
- •Proliferative Diabetic Retinopathy
- •Development and Natural History
- •Histopathology and Early Development
- •Proliferation and Regression of New Vessels
- •Contraction of the Vitreous and Fibrovascular Proliferations
- •Retinal Distortion and Detachment
- •Burned-Out Proliferative Diabetic Retinopathy
- •Systemic Associations
- •Proliferative Diabetic Retinopathy and Glycemic Control
- •Other Risk Factors for Proliferative Diabetic Retinopathy
- •Rubeosis Iridis
- •Anterior Hyaloidal Fibrovascular Proliferation
- •Management of Proliferative Diabetic Retinopathy
- •Pituitary Ablation
- •Photocoagulation
- •Randomized Clinical Trials of Laser Photocoagulation
- •The Diabetic Retinopathy Study
- •Risks and Benefits Photocoagulation In The Drs
- •The Early Treatment Diabetic Retinopathy Study
- •Indications For Photocoagulation of Pdr
- •PRP and Macular Edema
- •PRP Treatment Techniques
- •Vitrectomy for PDR
- •Pharmacologic Treatment of PDR
- •Acknowledgment
- •References
- •Brief Historical Background
- •The Wesdr
- •Prevalence of Diabetic Retinopathy
- •Incidence of Diabetic Retinopathy
- •Diabetic Retinopathy in African American and Hispanic Whites
- •Native Americans and Asian Americans
- •Age and Puberty
- •Genetic and Familial Factors
- •Modifiable Risk Factors
- •Hyperglycemia
- •Clinical Trials of Intensive Treatment of Glycemia
- •Diabetes Control and Complications Trial
- •The United Kingdom Diabetes Prospective Study (UKPDS)
- •Hypertension
- •Lipids
- •Subclinical and Clinical Diabetic Nephropathy
- •Microalbuminuria and Diabetic Retinopathy
- •Gross Proteinuria and Retinopathy
- •Diabetic Retinopathy as a Risk Indicator of Subclinical Nephropathy
- •Other Risk Factors For Retinopathy
- •Smoking and Drinking
- •Body Mass Index and Physical Activity
- •Hormone and Reproductive Exposures in Women
- •Prevalence and Incidence of Visual Impairment
- •Conclusions
- •Acknowledgments
- •References
- •Introduction
- •Fluorescein Angiography
- •Properties
- •Side Effects
- •Normal Fluorescein Angiography
- •Terminology
- •Fluorescein Angiography in the Evaluation of Diabetic Retinopathy
- •Fluorescein Angiography in the Evaluation of Diabetic Macular Edema
- •Optical Coherence Tomography
- •Low-Coherence Interferometry
- •OCT Image Interpretation
- •OCT Technology Development
- •The Role of OCT in Diabetic Macular Edema
- •Morphologic Patterns of Diabetic Macular Edema
- •Clinical Applications of OCT in Diabetic Macular Edema
- •Conclusions
- •References
- •Diabetic primates
- •Type of Diabetes
- •Histopathology and Rate of Development of the Retinopathy
- •Therapies Studied in this Model
- •Advantages and Disadvantages of the Model
- •Diabetic dogs
- •Type of Diabetes
- •Histopathology and Rate of Development of Retinopathy
- •Therapies Studied in this Model
- •Advantages and Disadvantages of the Model
- •Diabetic cats
- •Type of Diabetes
- •Histopathology and Rate of Development of Retinopathy
- •Therapies Studied in this Model
- •Advantages and Disadvantages of the Model
- •Diabetic rats
- •Type of Diabetes
- •Type 1 diabetes
- •Type 2 diabetes
- •Histopathology and Rate of Development of Retinopathy
- •Vascular disease
- •Neuronal disease
- •Therapies or Gene Modifications Studied in this Model
- •Advantages and Disadvantages of the Model
- •Diabetic mice
- •Type of Diabetes
- •Type 1 diabetes
- •Type 2 diabetes
- •Histopathology and Rate of Development of Retinopathy
- •Vascular disease
- •Neural disease
- •Therapies or Gene Modifications Studied in this Model
- •Advantages and Disadvantages of the Model
- •Other Rodents
- •Galactose Feeding
- •Nondiabetic Models in Which Growth Factors are Altered
- •VEGF overexpression
- •IGF overexpression
- •PDGF-B-deficient mice
- •Oxygen-Induced Retinopathy
- •Sympathectomy
- •Retinal Ischemia–Reperfusion
- •Summary
- •References
- •Introduction
- •Biochemistry and Genetics of The Polyol Pathway
- •Aldose Reductase
- •The Aldose Reductase Enzyme
- •The Aldose Reductase Gene
- •Polymorphisms of the AR Gene
- •Sorbitol Dehydrogenase
- •The Sorbitol Dehydrogenase Enzyme
- •The Sorbitol Dehydrogenase Gene
- •Ar Polymorphisms and Risk of Diabetic Retinopathy
- •Sdh Polymorphisms and Diabetic Retinopathy
- •Ar Overexpression
- •Sdh Overexpression
- •Ar “Knockout” Mice
- •Sdh-Deficient Mice
- •Osmotic Stress
- •Oxidative Stress
- •Activation of Protein Kinase C
- •Generation of AGE Precursors
- •Proinflammatory Events and Apoptosis
- •Ari Structures and Properties
- •Effects of Aris in Experimental Diabetic Retinopathy
- •The Polyol Pathway in Human Diabetic Retinopathy
- •The Sorbinil Trial
- •Perspective and Needs
- •Rationale for Defining the Pathogenic Role of the Polyol Pathway
- •Needs to be Met to Arrive at Anti-Polyol Pathway Therapy
- •References
- •Introduction to Diabetic Retinopathy
- •Biochemistry of Age Formation
- •Pathogenic Role of Ages In Diabetic Retinopathy
- •AGEs and Clinical Correlation of Diabetic Retinopathy
- •AGE Accumulation in the Eye
- •Effect of AGEs on Retinal Cells
- •RAGE in Diabetic Retinopathy
- •Other AGE Receptors in Diabetic Retinopathy
- •Anti-Age Strategies For Diabetic Retinopathy
- •Conclusion
- •References
- •Introduction
- •Dag-Pkc Pathway
- •Diabetes and Retinal Blood Flow
- •Basement Membrane and Ecm Changes
- •Vascular Permeability and Angiogenesis
- •Conclusions
- •References
- •Sources of Oxidative Stress in The Diabetic Retina
- •Overview
- •Mitochondrial Electron Transport Chain (ETC)
- •Advanced Glycation End (AGE) Product Formation
- •Cyclo-oxygenase (COX)
- •Flux Through Aldose Reductase (AR) Pathway
- •Activation of Protein Kinase C (PKC)
- •Endothelial NO Synthase (eNOS)
- •Inducible NOS (iNOS)
- •NADPH Oxidase
- •Antioxidants in Diabetic Retinopathy
- •Overview
- •Glutathione (GSH)
- •Superoxide Dismutase (SOD)
- •Catalase
- •Effects of Oxidative Stress in The Diabetic Retina
- •Overview
- •Growth Factors and Cytokines
- •Cytoxicity
- •Therapeutic Strategies For Reducing Oxidative Stress
- •Overview
- •Antioxidants
- •PKC Inhibitors
- •Inhibitors of the Renin-Angiotensin System
- •Inhibitors of the Polyol Pathway
- •HMG-CoA Reductase Inhibitors (Statins)
- •PEDF
- •Cannabinoids
- •Cyclo-oxygenase-2 (COX-2) Inhibitors
- •References
- •Pericyte Loss in the Diabetic Retina
- •Introduction
- •Origin and Differentiation
- •Morphology and Distribution
- •Identification
- •Function
- •Contractility
- •Role in Vessel Formation and Stabilization
- •Loss In Diabetic Retinopathy
- •Rats
- •Mice
- •Chinese Hamster
- •Animal Models Mimicking Retinal Pericyte Loss
- •Pdgf-B-Pdgf-Ssr
- •Angiopoietin-Tie
- •Vegf-Vegfr2
- •Mechanisms of Loss
- •Biochemical Pathways
- •Aldose Reductase
- •Age Formation
- •Modification of Ldl
- •Loss Through Active Elimination
- •Capillary Dropout in Diabetic Retinopathy
- •Diabetic Retinopathy
- •Methods to Measure and Detect Capillary Dropout
- •Models to Study Retinal Capillary Dropout in Diabetes
- •Potential Mechanisms For Capillary Dropout
- •Capillary Cell Apoptosis
- •Proinflammatory Changes/Leukostasis
- •Microthrombosis/Platelet Aggregation
- •Consequences of Capillary Dropout
- •Macular Ischemia
- •Neovascularization
- •Macular Edema
- •Acknowledgments
- •References
- •Neuroglial Dysfunction in Diabetic Retinopathy
- •The Neurons of The Retina
- •The Glial Cells of The Retina
- •Diabetes Reduces Retinal Function
- •Diabetes Induces Neurodegeneration in The Retina
- •Neuroinflammation in Diabetic Retinopathy
- •Historical Perspective on Diabetic Retinopathy
- •Neuroglial Dysfunction in Diabetic Retinopathy.
- •References
- •Introduction
- •Inflammatory Cells Promote and Regulate The Development of Ischemic Ocular Neovascularization
- •VEGF as a Proinflammatory Factor in Diabetic Retinopathy
- •VEGF164/165 as a Proinflammatory Cytokine
- •Nonsteroidal Anti-inflammatory Drugs (NSAIDs)
- •Corticosteroids
- •Anti-VEGF Agents
- •Pegaptanib
- •Ranibizumab and Bevacizumab
- •Conclusions
- •Acknowledgment
- •References
- •Glia-Endothelial Interaction
- •Specialized Retinal Vessels Control Flux into Neural Tissue
- •Overview of Tight Junction Proteins
- •Claudins Confer Tight Junction Barrier Properties
- •Occludin Regulates Barrier Properties
- •Alterations in Occludin in Diabetic Retinopathy
- •Ve-Cadherin and Diabetic Retinopathy
- •Permeability in Diabetic Retinopathy
- •Summary and Conclusions
- •References
- •Introduction
- •Stages of Angiogenesis
- •Vascular Endothelial Growth Factor
- •Regulation of Vegf Expression in The Retina
- •Regulation of VEGF in Proliferative Diabetic Retinopathy
- •Regulation of VEGF in Nonproliferative Diabetic Retinopathy
- •Basic Vegf Biology
- •Receptors
- •Vegf’S Multiple Actions on Retinal Endothelial Cells
- •Main Signaling Pathways
- •Other Actions of Vegf
- •Proinflammatory Effects of VEGF
- •VEGF and Retinal Neuronal Development
- •VEGF and Neuroprotection
- •Modulation of Vegf Action By Other Growth Factors
- •Conclusion
- •References
- •Insulin-Like Growth Factor
- •Basic Fibroblast Growth Factor
- •Angiopoietin
- •Erythropoietin
- •Hepatocyte Growth Factor
- •Tumor Necrosis Factor
- •Extracellular Proteinases
- •The Urokinase Plasminogen Activator System (uPA/uPAR System)
- •Proteinases in Retinal Neovascularization
- •Integrins
- •Endogenous Inhibitors of Neovascularization
- •Pigment Epithelium Derived Growth Factor
- •Angiostatin and Endostatin
- •Thrombospondin-1
- •Tissue Inhibitor of Matrix Metalloproteinases
- •Clinical Implications
- •Acknowledgments
- •References
- •Introduction
- •Pathogenesis
- •Vascular Endothelial Growth Factor (Vegf)
- •Vegf in Physiological and Pathological Angiogenesis
- •Vegf in Ocular Neovascularization
- •Vegf and Diabetic Retinopathy
- •Clinical Application of Anti-VEGF Drugs
- •Pegaptanib
- •Bevacizumab
- •Ranibizumab
- •Use of Anti-VEGF Therapies in Diabetic Retinopathy
- •Safety
- •Clinical Experience with Bevacizumab in Diabetic Retinopathy
- •Ranibizumab in Diabetic Macular Edema
- •Effect on Foveal Thickness and Macular Volume
- •Effect on Visual Acuity
- •Summary
- •References
- •Introduction
- •Pkc Inhibition With Ruboxistaurin
- •Early Clinical Trials With Rbx
- •Rbx and Progression of Diabetic Retinopathy
- •Ongoing Trials With Rbx
- •Rbx and Other, Nonocular Complications of Diabetes
- •Safety Profile of Rbx
- •Clinical Status of Rbx
- •Conclusions
- •References
- •The Role of Intravitreal Steroids in the Management of Diabetic Retinopathy
- •Clinical Efficacy
- •Safety
- •Pharmacology
- •Pharmacokinetics
- •Combination With Laser Treatment
- •Clinical Guidelines
- •Macular Edema Caused by Focal Parafoveal Leak
- •Widespread Heavy Diffuse Leak
- •Macular Edema and High-Risk Proliferative Retinopathy
- •Macular Edema Prior to Cataract Surgery
- •Juxtafoveal Hard Exudate With Heavy Leak
- •Control of Systemic Risk Factors
- •The Future of Intravitreal Steroid Therapy
- •References
- •Overview
- •Introduction and Historical Perspective
- •Growth Hormone and Diabetic Retinopathy
- •The IGF-1 System and Retinopathy
- •The Role of SST in Diabetic Retinopathy
- •Rationale for the Clinical use of Octreotide
- •Clinical evidence for sst as a therapeutic for pdr
- •Potential Reasons for Mixed Success in Clinical Trials
- •Future Direction: Sst Analogs in Combination Therapy
- •Conclusion
- •Acknowledgements
- •Introduction
- •Diabetic Retinopathy and Mortality
- •Diabetic Retinopathy and Cerebrovascular Disease
- •Diabetic Retinopathy and Heart Disease
- •Diabetic Retinopathy, Nephropathy, and Neuropathy
- •Conclusion
- •References
- •Name Index
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Klein |
diabetic retinopathy was significantly associated with renal structural endpoints such as glomerular basement membrane mesangial fractional volume while controlling for other risk factors such as age, diabetes duration, sex, glycosylated hemoglobin A1c, mean arterial blood pressure, and body mass index (BMI), suggesting that retinopathy may be a marker of subclinical renal disease.
OTHER RISK FACTORS FOR RETINOPATHY
Smoking and Drinking
Smoking, through its hypoxic effects on tissue and its effects on increasing platelet adhesiveness and aggregability, both hypothesized mechanisms involved in the pathogenesis of diabetic retinopathy, would be expected to be associated with retinopathy (133–135). However, most epidemiologic data do not show a relationship between cigarette smoking and a higher incidence or rate of progression of diabetic retinopathy (87, 88, 94, 96, 135–137). It is not known whether there are substances in cigarette smoke, such as nicotine, that neutralize the presumed detrimental effect of hypoxia and platelet dysfunction on retinopathy pathogenesis. Regardless, smoking should be discouraged in diabetic persons because of an increased risk of cardiovascular and respiratory disease and cancer. In the WESDR, while controlling for other risk factors, persons who smoked with type 1 diabetes or type 2 diabetes were 2.4 times and 1.6 times, respectively, as likely to die as those who did not smoke (138).
Alcohol through decreased platelet aggregation and adhesiveness might be thought of as having a possible protective effect in reducing the incidence and progression of retinopathy (139). However, no consistent relation between a history of alcohol consumption and retinopathy has been found. Data from some studies have shown alcohol to be beneficial, while others have shown no or a detrimental effect on risk of retinopathy (23, 140, 141). In the UKPDS, a relation of increased alcohol consumption to increased severity of retinopathy was found only in newly diagnosed men with type 2 diabetes (142). In the WESDR, there was no relationship between alcohol consumption at the 4-year examination and the incidence and progression of retinopathy in either persons with type 1 or 2 diabetes at the 10-year follow-up (143). With lack of a harmful effect of moderate alcohol consumption on retinopathy, the finding in the WESDR of a protective effect on cardiovascular disease mortality in persons with type 2 diabetes suggests that such behavior might be of benefit (144).
Inflammation and Endothelial Dysfunction and Cellular
Adhesion Molecules
Inflammatory processes have been hypothesized to be involved in the pathogenesis of diabetic retinopathy (145, 146). Elevations in the level of markers of inflammation attributed to hyperglycemia, advanced glycation end-products, and increased BMI (147, 148) have been found in persons with type 1 diabetes (146–148). While inflammatory biomarkers such as serum fibrinogen, tumor necrosis factor alpha (TNF-α), and C-reactive protein (CRP) may be elevated, there are few data regarding the role of inflammation in the progression of diabetic retinopathy (148–152). In two case–control studies, diabetic subjects with macular edema (151) or PDR (150) had higher levels of
The Epidemiology of Diabetic Retinopathy |
95 |
vascular endothelial growth factors and cytokines in their vitreous than those without macular edema or PDR. In a cross-sectional study of normotensive persons with type 1 diabetes, CRP and fibrinogen levels were positively associated with diabetic retinopathy severity (148). In a case series of 93 diabetic patients, serum chemokines were significantly elevated in patients with at least severe nonproliferative diabetic retinopathy compared with those who had less severe retinopathy (153). Data from the Hoorn study in persons with type 2 diabetes also showed retinopathy to be associated with serum CRP and soluble intercellular adhesion molecule-1 (sICAM-1) levels, a marker of endothelial dysfunction (154). While some treatments for chronic macular edema have been focused on use of intravitreal anti-inflammatory agents, e.g., steroids, there are few data showing that decreasing inflammatory activity stops the development or progression of diabetic retinopathy or restores visual acuity.
Endothelial dysfunction may result in increased vascular permeability, alteration of blood flow, oxidative stress, and angiogenesis and has been postulated to play a role in the pathogenesis of diabetic retinopathy (155–162). Endothelial dysfunction is characterized by elevated levels of several systemic markers (e.g., von Willebrand factor, Factor VIII, soluble E-selectin). In addition, homocysteine levels, which have been found to be elevated in persons with type 1 diabetes, have been shown to damage endothelial cells via generation of hydrogen peroxide (162, 163). Homocysteine, von Willebrand factor, and other markers of endothelial dysfunction have been inconsistently associated with the prevalence, severity, and incidence of diabetic retinopathy (148, 164–172). Fewer data are available about potentially protective factors such as folate and vitamins B12 and B6 levels for progression of retinopathy and incidence of proliferative retinopathy in persons with diabetes (166, 170).
Leucocyte adherence to retinal endothelium has been postulated as a cause of capillary occlusion, a factor in the pathogenesis of diabetic retinopathy (173). Adherence of leucocytes to capillary and arteriolar endothelium occurs as a result of a process involving expression of adhesion molecules (e.g., selectins, intercellular adhesion molecules [ICAM-1], and vascular cell adhesion molecules [VCAM]-1) (174–179). Levels of two adhesion molecules, soluble E-selectin and soluble VCAM-1, have been shown to be elevated in patients with type 1 diabetes with more severe retinopathy (153, 180). However, there are neither prospective nor population-based data showing that elevation in concentrations of these molecules precedes the progression of retinopathy nor whether these associations remain while controlling for glycosylated hemoglobin, blood pressure levels, and signs of diabetic nephropathy.
Body Mass Index and Physical Activity
Data from epidemiological studies show that when other risk factors, e.g., hyperglycemia and hypertension, are controlled for, neither BMI, a measure of obesity, nor physical activity are associated with a higher risk of diabetic retinopathy (13, 87, 88, 131, 181–187).
Hormone and Reproductive Exposures in Women
The evidence to date suggests that estrogen exposure is not associated with risk of retinopathy. Use of oral contraceptives, which contain estrogens as well as progestins,