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Файл:Ординатура / Офтальмология / Учебные материалы / Section 3 Clinical Optics 2015-2016.pdf
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- •Contents
- •General Introduction
- •Objectives
- •1 Geometric Optics
- •Rays, Refraction, and Reflection
- •Introduction
- •Point Sources, Pencils, and Beams of Light
- •Object Characteristics
- •Image Characteristics
- •Magnification
- •Image Location
- •Depth of Focus
- •Image Quality
- •Light Propagation
- •Optical Media and Refractive Index
- •Law of Rectilinear Propagation
- •Optical Interfaces
- •Law of Reflection (Specular Reflection)
- •Law of Refraction (Specular Transmission)
- •Normal Incidence
- •Total Internal Reflection
- •Dispersion
- •Reflection and Refraction at Curved Surfaces
- •The Fermat Principle
- •Pinhole Imaging
- •Locating the Image: The Lensmaker’s Equation
- •Ophthalmic Lenses
- •Vergence
- •Reduced Vergence
- •Thin-Lens Approximation
- •Lens Combinations
- •Virtual Images and Objects
- •Focal Points and Planes
- •Paraxial Ray Tracing Through Convex Spherical Lenses
- •Paraxial Ray Tracing Through Concave Spherical Lenses
- •Objects and Images at Infinity
- •Principal Planes and Points
- •Section Exercises
- •Focal Lengths
- •Gaussian Reduction
- •Knapp’s Law, the Badal Principle, and the Lensmeter
- •Afocal Systems
- •Section Exercises
- •Questions
- •Power of a Lens in a Medium
- •Spherical Interface and Thick Lenses
- •Thick Lens
- •Back Vertex Power Is Not True Power
- •Aberrations of Ophthalmic Lenses
- •Third-Order Seidel Aberrations
- •Chromatic Aberrations
- •Avoiding Aberrations
- •Mirrors
- •Reflection From a Plane Mirror
- •Spherically Curved Mirrors
- •Reversal of the Image Space
- •The Central Ray for Mirrors
- •Vergence Calculations for Mirrors
- •Spherocylindrical Lenses
- •Combination of Spherocylindrical Lenses
- •The Conoid of Sturm
- •The Jackson Cross Cylinder
- •Prisms
- •Prism Diopter
- •Prismatic Effect of Lenses and the Prentice Rule
- •Prism Aberrations
- •Fresnel Prisms
- •Chapter Exercises
- •Questions
- •Appendix 1.1
- •Quick Review of Angles, Trigonometry, and the Pythagorean Theorem
- •Appendix 1.2
- •Light Properties and First-Order Optics
- •2 Optics of the Human Eye
- •The Human Eye as an Optical System
- •Schematic Eyes
- •Important Axes of the Eye
- •Pupil Size and Its Effect on Visual Resolution
- •Visual Acuity
- •Contrast Sensitivity and the Contrast Sensitivity Function
- •Refractive States of the Eyes
- •Binocular States of the Eyes
- •Accommodation and Presbyopia
- •Epidemiology of Refractive Errors
- •Developmental Myopia
- •Developmental Hyperopia
- •Prevention of Refractive Errors
- •Chapter Exercises
- •Questions
- •3 Clinical Refraction
- •Objective Refraction Technique: Retinoscopy
- •Positioning and Alignment
- •Fixation and Fogging
- •The Retinal Reflex
- •The Correcting Lens
- •Finding Neutrality
- •Retinoscopy of Regular Astigmatism
- •Aberrations of the Retinoscopic Reflex
- •Subjective Refraction Techniques
- •Astigmatic Dial Technique
- •Stenopeic Slit Technique
- •Cross-Cylinder Technique
- •Refining the Sphere
- •Binocular Balance
- •Cycloplegic and Noncycloplegic Refraction
- •Overrefraction
- •Spectacle Correction of Ametropias
- •Spherical Correcting Lenses and the Far Point Concept
- •The Importance of Vertex Distance
- •Cylindrical Correcting Lenses and the Far Point Concept
- •Prescribing for Children
- •Myopia
- •Hyperopia
- •Anisometropia
- •Clinical Accommodative Problems
- •Presbyopia
- •Accommodative Insufficiency
- •Accommodative Excess
- •Accommodative Convergence/Accommodation Ratio
- •Effect of Spectacle and Contact Lens Correction on Accommodation and Convergence
- •Prescribing Multifocal Lenses
- •Determining the Add Power of a Bifocal Lens
- •Types of Bifocal Lenses
- •Trifocal Lenses
- •Progressive Addition Lenses
- •The Prentice Rule and Bifocal Lens Design
- •Occupation and Bifocal Segment
- •Prescribing Special Lenses
- •Aphakic Lenses
- •Absorptive Lenses
- •Special Lens Materials
- •Therapeutic Use of Prisms
- •Chapter Exercises
- •Questions
- •Appendix 3.1
- •Common Guidelines for Prescribing Cylinders for Spectacle Correction
- •4 Contact Lenses
- •Introduction
- •Contact Lens Glossary
- •Clinically Important Features of Contact Lens Optics
- •Field of Vision
- •Image Size
- •Accommodation
- •Convergence Demands
- •Tear Lens
- •Correcting Astigmatism
- •Correcting Presbyopia
- •Contact Lens Materials and Manufacturing
- •Materials
- •Manufacturing
- •Patient Examination and Contact Lens Selection
- •Patient Examination
- •Contact Lens Selection
- •Contact Lens Fitting
- •Soft Contact Lenses
- •Rigid Gas-Permeable Contact Lenses
- •Toric Soft Contact Lenses
- •Contact Lenses for Presbyopia
- •Keratoconus and the Abnormal Cornea
- •Contact Lens Overrefraction
- •Gas-Permeable Scleral Contact Lenses
- •Therapeutic Lens Usage
- •Orthokeratology and Corneal Reshaping
- •Custom Contact Lenses and Wavefront Technology
- •Contact Lens Care and Solutions
- •Contact Lens–Related Problems and Complications
- •Infections
- •Hypoxic/Metabolic Problems
- •Toxicity
- •Mechanical Problems
- •Inflammation
- •Chapter Exercises
- •Questions
- •Appendix 4.1
- •Transmission of Human Immunodeficiency Virus in Contact Lens Care
- •Appendix 4.2
- •Federal Law and Contact Lenses
- •5 Intraocular Lenses
- •Intraocular Lens Designs
- •Classification
- •Background
- •Optical Considerations for Intraocular Lenses
- •Intraocular Lens Power Calculation
- •Piggyback and Supplemental Intraocular Lenses
- •Intraocular Lens Power Calculation After Corneal Refractive Surgery
- •Instrument Error
- •Index of Refraction Error
- •Formula Error
- •Power Calculation Methods for the Post–Keratorefractive Procedure Eye
- •Intraocular Lens Power in Corneal Transplant Eyes
- •Silicone Oil Eyes
- •Pediatric Eyes
- •Image Magnification
- •Lens-Related Vision Disturbances
- •Nonspherical Optics
- •Multifocal Intraocular Lenses
- •Types of Multifocal Intraocular Lenses
- •Clinical Results of Multifocal Intraocular Lenses
- •Accommodating Intraocular Lenses
- •Intraocular Lens Standards
- •Chapter Exercises
- •Questions
- •Appendix 5.1
- •History of Intraocular Lens Design
- •6 Optical Considerations in Keratorefractive Surgery
- •Corneal Shape
- •Angle Kappa
- •Pupil Size
- •Irregular Astigmatism
- •Application of Wavefront Analysis in Irregular Astigmatism
- •Causes of Irregular Astigmatism
- •Conclusion
- •Chapter Exercises
- •Questions
- •7 Optical Instruments and Low Vision Aids
- •Magnification
- •Telescopes
- •Galilean Telescope
- •Astronomical Telescope
- •Accommodation Through a Telescope
- •Surgical Loupe
- •General Principles of Optical Engineering
- •Terminology
- •Measurements of Performance of Optical Systems
- •Optical Instruments and Techniques Used in Ophthalmic Practice
- •Direct Ophthalmoscope
- •Indirect Ophthalmoscope
- •Fundus Camera
- •Slit-Lamp Biomicroscope
- •Gonioscopy
- •Surgical Microscope
- •Geneva Lens Clock
- •Lensmeter
- •Knapp’s Rule
- •Optical Pachymeter
- •Applanation Tonometry
- •Specular Microscopy
- •Keratometer
- •Topography
- •Ultrasonography of the Eye and Orbit
- •Macular Function Tests
- •Scanning Laser Ophthalmoscopes
- •Scheimpflug Camera
- •Autorefractors
- •Optical Coherence Tomography
- •Optical Aids
- •Magnifiers
- •Telescopes
- •Prisms
- •High-Add Spectacles
- •Nonoptical Aids
- •Electronic Devices
- •Lighting, Glare Control, and Contrast Enhancement
- •Nonvisual Assistance
- •Eccentric Viewing or Fixation Training
- •Instruction and Training
- •Chapter Exercises
- •Questions
- •Appendix 7.1
- •Approach to the Patient With Low Vision
- •8 Physical Optics
- •The Corpuscular Theory of Light
- •Diffraction
- •The Speed of Light
- •The Superposition of Waves
- •Coherence
- •Electromagnetic Waves
- •Polarization
- •Refractive Index and Dispersion
- •Reflection, Transmission, and Absorption
- •The Electromagnetic Spectrum
- •Frequency and Color
- •Energy in an Electromagnetic Wave
- •Quantum Theory
- •Light Sources
- •Thermal Sources
- •Luminescent Sources
- •Fluorescence
- •Phosphorescence
- •Lasers
- •Light–Tissue Interactions
- •Photocoagulation
- •Photoablation
- •Photodisruption
- •Photoactivation
- •Light Scattering
- •Rayleigh Scattering
- •Mie Scattering
- •The Tyndall Effect
- •Radiometry and Photometry
- •Light Hazards
- •Clinical Applications
- •Polarization
- •Interference
- •Diffraction
- •Imaging and the Point Spread Function
- •Image Quality—Modulation Transfer Function
- •Chapter Exercises
- •Questions
- •Appendix 8.1
- •Radiometric and Photometric Units
- •Basic Texts
- •Related Academy Materials
- •Requesting Continuing Medical Education Credit
Figure 6-7 Irregular astigmatism in a corneal topographic map of the left eye of a patient with significant epithelial basement membrane dystrophy. The patient experienced glare and a general decline in quality of vision. Simulated K shows the flattest meridian at 39° and the steeper meridian at 129°. N = nasal; T = temporal. (Courtesy of Ming Wang, MD.)
To normalize wavefront aberration measurements and improve postoperative visual quality in patients undergoing keratorefractive surgery, ophthalmologists are developing technologies to improve the accuracy of higher-order aberration measurements and treatment by using “flying spot” excimer lasers. Such lasers use small spot sizes (<1-mm diameter) to create smooth ablations, addressing the minute topographic changes associated with aberration errors.
For a more detailed discussion of the topics covered in this subsection, see BCSC Section 13,
Refractive Surgery.
Causes of Irregular Astigmatism
Irregular astigmatism may be present before keratorefractive surgery; it may be caused by the surgery; or it may develop postoperatively. Preoperative causes include keratoconus, pellucid marginal
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