Image Modeling of the Human Eye

Image Modeling of the Human Eye Rajendra Acharya U Eddie Y. K. Ng Jasjit S. Suri Editors ARTECH H O U S E BOSTON LONDON artechhouse.com

Contents Preface xiiii CHAPTER1 The Human Eye 1.1 1.2 1. 1.4 1.5 Basic Ocular Anatomy and Physiology 1 1.1.1 1.1.2 1.1. 1.1.4 1.1.5 1.1.6 The Cornea The Aqueous Humor The Iris TheLens The Vitreous Humor The Sclera 1 Cornea 4 1.2.1 Retina 1..1 1..2 1.. Structure of the Cornea Structure of the Retina Organization of Neuronal Cell Layers Path of Visual Signals 4 5 6 7 8 Anterior Segment Abnormalities 9 1.4.1 1.4.2 1.4. 1.4.4 1.4.5 1.4.6 1.4.7 1.4.8 Keratoconus Corneal Ulcer Fuchs'Dystrophy Pterygium and Pingueculae Scleritis Uveitis Corneal Haze Cataracts 9 11 1 1 14 17 18 19 Posterior Segment Abnormalities 22 1.5.1 1.5.2 1.5. 1.5.4 1.5.5 Diabetic Retinopathy Macular Degeneration Retinal Detachment Floaters Glaucoma 22 2 29 1 2 References 5 CHAPTER 2 Introduction to Imaging Optics 7 2.1 Properties of Light 7 V

VI Contents 2.1.1 Refraction 8 2.1.2 Angle of Refraction 9 2.1. Critical Angle and Total Internal Reflection 40 2.1.4 Loss of Energy 41 2.1.5 Dispersion of Light into a Spectrum 41 2.2 Redirection of the Light Ray 42 2.2.1 Basic Prism 42 2.2.2 Optical Wedge 42 2.2. Reflecting Surfaces 4 2.2.4 The Reflected Image 4 2.2.5 Double Reflection 44 2. Practical Prisms 45 2..1 Amici (Roof Edge) Prism 47 2..2 Schmidt Prism 47 2.. Penta Prism 48 2..4 Cube Beam Splitters 48 2..5 Lateral Displacement Beam Splitters 49 2.4 Basic Imaging (First-Order Paraxial Optics) 50 2.4.1 Cardinal (Gauss) Points and Focal Length 50 2.4.2 Image Formation Using a Positive Lens 51 2.4. Optical Axis, Chief Rays, and Marginal Rays 52 2.4.4 Aperture Stop 5 2.4.5 Iris 5 2.4.6 Entrance and Exit Pupils 5 2.4.7 Vignetting 54 2.5 Real Images 54 2.6 Physical Devices and Their Effects 56 2.6.1 Aperture and Lens Hood 57 2.6.2 Obstruction 57 2.7 Virtual Images 59 2.7.1 Converting a Virtual Image into a Real Image 59 2.7.2 Minimum and Maximum Separation Between Lenses 59 2.7. Virtual Image at Infinity 61 2.7.4 Vignetting Due to Eye Position 61 2.8 Controlled Size Imaging 61 2.8.1 Adding an Objective (Convex) Lens to Increase Image Size 62 2.8.2 Multiple Lens Imaging 6 2.8. A Practical Three-Lens System 64 2.9 Lasers 66 2.9.1 Generation of a Laser 66 References 69 CHAPTER Eye Imaging Systems 71.1 Computed Tomography 71.1.1 Principle 72.1.2 Applications 76

.1. Advantages.1.4 Limitations.2 Confocal Laser Scanning Microscopy.2.1 Principle.2.2 Applications.2. Advantages.2.4 Limitations. Magnetic Resonance Imaging..1 Principle..2 Applications.. Advantages..4 Limitations.4 Optical Coherence Tomography.4.1 Principles.4.2 Applications.4. Advantages.4.4 Limitations.5 Ultrasound Imaging.5.1 Principle.5.2 Color Doppler Imaging.5. Applications.5.4 Advantages.5.5 Limitations.6 Discussion.7 Conclusions References Automatic Identification of Anterior Segment Eye Abnormalities Optical Images 4.1 Introduction 4.2 Data Acquisition 4. Preprocessing 4..1 Histogram Equalization 4..2 Binarization 4.4 Features Used for the Classification 4.4.1 Big Ring Area 4.4.2 Small Ring Area 4.4. Homogeneity 4.4.4 BW Morph 4.5 Artificial Neural Network-Based Classifier 4.5.1 Backpropagation Learning Algorithm 4.6 Results 4.7 Discussion 4.8 Conclusions References

VIII Contents CHAPTER 5 Identification of Different Stages of Diabetic Retinopathy Using Retinal Optical Images 115 5.1 Introduction 115 5.2 Computer Methods and Theory 117 5.2.1 Imaging Techniques 118 5.2.2 Features 119 5. System Description 121 5..1 Gaussian Mixture Model for Classification 121 5.4 Statistics of System 12 5.5 Discussion 124 5.6 Conclusions 128 References 128 CHAPTER 6 Computer-Based Detection of Diabetes Maculopathy Stages Using Higher-Order Spectra 1 1 6.1 Introduction 11 6.1.1 Nonclinically Significant Maculopathy 1 6.1.2 Clinically Significant Maculopathy 14 6.2 Data Acquisition and Processing 15 6.2.1 - Preprocessing of Image Data 16 6.2.2 Feature Extraction 16 6.2. Higher-Order Spectra (HOS) 17 6.2.4 Fuzzy Classifier 19 6. Results 140 6.4 Discussion 142 6.5 Conclusions 142 Acknowledgments 14 References 14 CHAPTER 7 Algorithms for Detecting Glaucomatous Structural Changes in the Optic Nerve Head 147 7.1 Anatomy of the Eye and Pathophysiology of Glaucoma 148 7.1.1 Anatomy of the Eye 148 7.1.2 Pathophysiology of Glaucoma 149 7.2 Morphological Changes in the ONH Region in Glaucoma 151 7.2.1 Optic Disc Configuration 151 7.2.2 Retinal Nerve Fiber Layer Defects 15 7.2. Parapapillary Atrophy and Optic Disc Hemorrhages 15 7. Confocal Scanning Laser Ophthalmoscope for ONH Analysis 154 7..1 Principle of Confocal Microscopy 155 7..2 Measuring Optic Disc Stereometrie Parameters from the CSLO Optic Disc Topographs 157 7.. Algorithms for Detecting Glaucomatous Damage of the ONH 160 7.4 Algorithms for Detecting Glaucomatous Progression in the ONH 162

Contents IX 7.4.1 Essential Qualities of the Computational and Statistical Methods Applied for Detecting Glaucomatous Structural Changes 16 7.4.2 Stereometrie Parameter-Based Progression Analysis 16 7.4. Topographie Change Analysis (TCA) 167 7.4.4 Nonparametric Permutation Tests Progression Analysis 17 7.5 Summary 181 Acknowledgments 184 References 184 CHAPTER 8 Fractal Measures for Fungal Keratitis Diagnosis Using a White-Light Confocal Microscope 189 8.1 Introduction 189 8.2 A Computational Framework for Identifying Filamentous Fungi in Corneal Confocal Images 192 8.2.1 Fungal Feature Extraction 192 8.2.2 Fractal Dimension Based Feature Metrics 195 8. Image Classification 196 8.4 Results 197 8.5 Conclusions and Future Work 198 Acknowledgments 201 References 201 CHAPTER 9 Vessel Detection Experiments Using a Gaussian Matched Filter 20 9.1 Spatial Filters for the Detection of Blood Vessels 20 9.2 Estimation of Filter Parameters 206 9.2.1 True Versus False Vessels 207 9.2.2 Some Filter Parameters 210 9. Best Rotation for Filter 1 210 9.4 Band Selection of the Retinal Image 211 9.5 Best Threshold for Segmenting the Vessel Image 211 9.6 Summary 21 References 214 CHAPTER10 Detection of Retinal Blood Vessels Using Gabor Filters 215 10.1 Introduction 215 10.1.1 Retinopathy 215 10.1.2 Detection of Retinal Blood Vessels 216 10.2 Methods 217 10.2.1 Gabor Filters for the Detection of Oriented Patterns 217 10.2.2 Procedure for the Detection of Retinal Blood Vessels 218 10. Experiments and Results 220 10..1 Data Set of Retinal Images and Preprocessing 220 10..2 Single-Scale Filtering and Analysis 220 10.. Multiscale Filtering and Analysis 222

X Contents 10.4 Discussion and Conclusions 22 Acknowledgments 224 References 224 CHAPTER11 Finite Element Simulation of the Eye Structure with Bioheat Analysis: Two- and Three-Dimensional Ocular Surface Temperature Profiles 229 11.1 Introduction 229 11.2 Previously Developed Models 20 11. Development of the Human Eye Model 21 11.4 Mathematical Description 25 11.4.1 Governing Equation 25 11.4.2 Boundary Conditions 25 11.4. Additional Assumptions 27 11.5 Numerical Methodology 27 11.6 Steady-State Temperature Distribution 28 11.7 Sensitivity Analysis 242 11.7.1 Effects of Lens Thermal Conductivity 24 11.7.2 Effects of Blood Convection Coefficient 24 11.7. Effects of Ambient Convection Coefficient 244 11.7.4 Effects of Blood Temperature 244 11.7.5 Effects of Ambient Temperature 245 11.7.6 Effects of Tear Evaporation Rate 245 11.7.7 Summary from Sensitivity Analysis Study 246 11.8 Effects of EM Wave Exposure on the Human Eye 246 11.8.1 Governing Equations and Boundary Conditions 247 11.8.2 Results and Discussion 247 11.9 Summary 249 References 250 CHAPTER 12 Variations of the Corneal Surface Temperature with Contact Lens Wear 25 12.1 Introduction 25 12.2 A Brief History of Contact Lens 254 12. Tear Film and Tear Evaporation 254 12.4 Contact Lens and Corneal Surface Temperature 255 12.5 The Contact Lens Model 256 12.5.1 Model Development 256 12.5.2 Governing Equation and Boundary Conditions 256 12.5. Numerical Methodology 260 12.6 Numerical Predictions and Analysis 261 12.6.1 Steady-State Analysis 261 12.6.2 Transient Analysis 262 12.7 Summary and Discussion 265 References 266

XI CHAPTER1 An Axisymmetric Boundary Element Model for Bioheat Transfer in the Human Eye 269 1.1 Introduction 269 1.2 The Axisymmetric Human Eye Model 270 1.2.1 The Governing Equation 271 1. The Axisymmetric Boundary Element Method 27 1.4 Numerical Results and Analysis 276 1.5 Sensitivity Analysis 278 1.5.1 Effects of Lens Thermal Conductivity 279 1.5.2 Effects of Ambient Temperature 279 1.5. Effects of Blood Temperature 280 1.5.4 Effects of Ambient Convection Coefficient 280 1.5.5 Effects of Blood Convection Coefficient 281 1.5.6 Effects of Tear Evaporation 282 1.6 Discussion and Conclusions 282 References 284 CHAPTER14 Simulation of Aqueous Humor Circulation Inside the Human Eye 287 14.1 Introduction 287 14.2 The Human Eye Model 288 14.2.1 Governing Equations 288 14.2.2 Boundary Conditions 290 14.2. Aqueous Humor Hydrodynamics 292 14. Numerical Methodology 292 14.4 Results and Analysis 292 14.4.1 The Effects of Aqueous Humor Circulation 292 14.4.2 The Effects of Eye Orientation 294 14.5 Discussion 296 14.6 Conclusions 298 References 299 CHAPTER 15 Clinical Implications for Thermography in the Eye World: A Short History of Clinical Ocular Thermography 01 15.1 Introduction 01 15.1.1 Early Techniques of Ocular Temperature Assessment 01 15.1.2 Noncontact Ocular Temperature Measurement 04 15.1. Converting Radiation Readings to Temperatures 05 15.2 Ocular Thermography 06 15.2.1 TypicalOST 07 15.2.2 The Influence of the Environment on OST 12 15.2. Individual Variations in OST 1 15. Ocular Disease and Ocular Temperature 1 15.4 Summary 14 References 15

XII Contents CHAPTER 16 Temperature Measurement of the Anterior Eye During Hydrogel Contact Lens Wear 16.1 Introduction 16.2 Method 16.2.1 Study Population 16.2.2 Study Design and Procedure 16.2. Data Acquisition and Analysis 16. Results 16.4 Discussion 16.4.1 Possible Clinical Relevance 16.5 Conclusions References CHAPTER 17 Variations of C >cular Surface Temperature with Different Age Groups 17.1 Introduction 17.1.1 Variations of Ocular Surface Temperature with Age 17.1.2 Clinical Applications 17.2 Methodology 17.2.1 Equipment Specifications 17.2.2 Reference Emitter Technique 17.2. Test Subjects 17. Results and Discussion 17..1 Effectiveness of Infrared Cameras in Ocular Surface Thermography 17.4 Conclusions Acknowledgments References 19 20 20 20 22 2 2 25 26 27 27 1 1 2 4 4 4 5 6 40 40 41 41 About the Editors List of Contributors ndex 45 47 49