OCT Angiography E-Book

David Chow

• Herausgeber: Thieme Medical Publishers
• Kategorie: Fachliteratur
• Sprache: Englisch

Veröffentlichungsjahr: 2017

Beschreibung

The definitive guide on state-of-the-art OCT angiography from leading worldwide experts

OCT Angiography by David R. Chow and a cadre of renowned authors is an authoritative, richly illustrated guide on a groundbreaking new ophthalmic imaging technique. Optical coherence tomography angiography is revolutionizing ophthalmologic diagnosis and management of retinal disease. The technology is transforming the ocular disease diagnostic paradigm - from the retina to the choroid - enabling precision-tailored patient management.

Noninvasive and more sophisticated than fluorescein angiography, OCTA obviates the need for dye and yields an unprecedented level of detail. The layered visualization of the retina and choroid vasculature delivers greater understanding of retinal disease. From sight-robbing eye diseases affecting millions such as age-related macular degeneration, diabetic retinopathy, and glaucoma - to rare conditions like adult-onset vitelliform macular dystrophy, readers will glean insights on the capabilities of this remarkable innovation.

Key Features

• Hands-on pearls from trailblazers who have pioneered and implemented the use of OCTA in clinical practice
• Dedicated chapters on AMD, diabetic retinopathy, retinal venous occlusions, arterial occlusions, central serous chorioretinopathy, macular telangiectasia type 2, adult-onset vitelliform macular dystrophy, and high myopia
• Expanding indications for uveitis, ocular oncology, radiation retinopathy, glaucoma, the anterior segment, as well as future applications
• Grand Rounds cases include a wealth of multimodal images and highly informative learning points

This exceptional resource is a must-have for every ophthalmology resident and practitioner. The comprehensive text coupled with high quality illustrations will enable ophthalmologists to leverage the full potential of this technique in daily practice.

Leseprobe

OCT Angiography

David R. Chow, MD, FRCSC

Assistant ProfessorDepartment of OphthalmologySt. Michaels HospitalUniversity of TorontoFellowship Director and Co-DirectorToronto Retina InstituteToronto, Ontario, Canada

Paulo Ricardo Chaves de Oliveira, MD

Ophthalmology degreeFaculdade de Ciências Médicas da Santa Casa de São PauloRetinal FellowshipRetina Clinic, São PauloUveitis FellowshipFederal University of São Paulo (UNIFESP)Retinal Research FellowToronto Retina Institute, CanadaRetinal SpecialistInstituto Panamericano da VisãoGoiânia, Brazil

ThiemeNew York • Stuttgart • Delhi • Rio de Janeiro

Executive Editor: William LamsbackManaging Editor: Haley PaskalidesDirector, Editorial Services: Mary Jo CaseyProduction Editor: Sean WoznickiInternational Production Director: Andreas SchabertEditorial Director: Sue HodgsonInternational Marketing Director: Fiona HendersonInternational Sales Director: Louisa TurrellDirector of Institutional Sales: Adam BernackiSenior Vice President and Chief Operating Officer:Sarah VanderbiltPresident: Brian D. Scanlan

Library of Congress Cataloging-in-Publication DataNames: Chow, David R., editor. | Oliveira, Paulo Ricardo   Chaves de, editor.Title: OCT angiography/[edited by] David R. Chow, Paulo   Ricardo Chaves de Oliveira.Description: New York, NY: Thieme Medical Publishers, Inc.,   [2018] | Includes bibliographical references.Identifiers: LCCN 2017032576| ISBN 9781626234734 (print) | ISBN 9781626234741 (e book)Subjects: | MESH: Retinal Diseases–diagnostic imaging | Tomography, Optical Coherence | Computed Tomography Angiography | Eye Diseases–diagnostic imaging | Retinal Vessels–diagnostic imaging | Case ReportsClassification: LCC RE79.I42 | NLM WW 270 | DDC 616.07/545–dc23 LC record available at https://lccn.loc.gov/2017032576

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Also available as an e-book:eISBN 978-1-62623-474-1

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Any significant effort or venture requires a lot of help to do properly. This textbook was no different. I would like to thank the authors who provide authoritative views on their areas of expertise and do so for only academic and educational reasons. Paulo Oliveira was my research fellow from Brazil who helped me get this done. It would not have happened without him. Thanks Paulo! And to my family who see me running all over the place. Don't forget you are all more important to me than anything I do at work.

Contents

Preface

Contributors

1      Optical Coherence Tomography Angiography: Understanding the Basics

David R. Chow

1.1    Introduction

1.2    So What Is Optical Coherence Tomography Angiography and Why Is It So Exciting?

1.3    Making Sense of the Information Obtained in an OCTA

1.4    Nomenclature

1.5    Limitations of Optical Coherence Tomography Angiography

1.6    Anatomic Discoveries in Normal Eyes with Optical Coherence Tomography Angiography

1.6.1   Central versus Temporal Macula

1.6.2   Size of the foveal avascular zone

1.6.3   Radial Peripapillary Capillary Network

1.6.4   Vascular Pattern of the Superficial versus Deep Retinal Plexus

1.7    Conclusion

References

2      Optical Coherence Tomography Angiography Artifacts

Paulo Ricardo Chaves de Oliveira, Keyvan Koushan, André Maia, and David R. Chow

2.1    Introduction

2.2    How does Optical Coherence Tomography Angiography work?

2.3    Motion Artifacts

2.4    Projection Artifacts

2.5    Shadowing/Masking Effect

2.6    Segmentation Artifact

2.7    Other Considerations

References

3      Current Optical Coherence Tomography Angiography Clinical Systems

Sumit Sharma and Peter K. Kaiser

3.1    Introduction

3.2    Optovue AngioVue

3.3    Carl Zeiss Meditec AngioPlex

3.4    Nidek RS-3000 Advance Optical Coherence Tomography

3.5    Topcon DRI OCT Triton

3.6    Others

3.7    Comparisons

3.8    Conclusion

3.9    Financial Disclosures

References

4      Optical Coherence Tomography Angiography and Neovascular Age-Related Macular Degeneration

Nicholas A. Iafe, Nopasak Phasukkijwatana, and David Sarraf

4.1    Introduction

4.2    OCTA Features of Neovascular Age-Related Macular Degeneration

4.2.1   Type 1 Neovascular Age-Related Macular Degeneration

4.2.2   Type 2 Neovascular Age-Related Macular Degeneration

4.2.3   Type 3 Neovascular Age-Related Macular Degeneration

4.3    Assessing Neovascular Activity with Optical Coherence Tomography Angiography

4.4    Conclusion

References

5      Optical Coherence Tomography Angiography and Fibrotic Choroidal Neovascularization in Age-Related Macular Degeneration

Eric Souied and Alexandra Miere

5.1    Introduction

5.2    Subretinal Fibrosis

References

6      Nonneovascular Age-Related Macular Degeneration

Ricardo Noguera Louzada, Mark Lane, and Nadia K. Waheed

6.1    Introduction

6.2    Early Nonneovascular Age-Related Macular Degeneration

6.3    Optical Coherence Tomography Angiography in Dry AMD

6.4    Geographic Atrophy

6.5    Varying Interscan Time Analysis

6.6    Conclusion

References

7      Optical Coherence Tomography Angiography and Diabetic Retinopathy

André Romano

7.1    Introduction

7.2    Optical Coherence Tomography Angiography Technique

7.3    Nonproliferative Diabetic Retinopathy

7.3.1   Microaneurysms

7.3.2   Macular Edema

7.3.3   Intraretinal Microvascular Abnormalities

7.4    Proliferative Diabetic Retinopathy

7.5    Ischemic Diabetic Maculopathy

7.6    Quantitative Capillary Perfusion Density Mapping (AngioAnalytics)

7.7    Conclusion

References

8      Optical Coherence Tomography Angiography and Arterial Occlusions

Abtin Shahlaee, Carl D. Regillo, and Allen C. Ho

8.1    Overview of Vascular Anatomy

8.2    Pathogenesis and Diagnosis

8.3    Features of Arterial Occlusion on Optical Coherence Tomography Angiography

8.4    Deep Capillary Ischemia

8.5    Limitations

8.6    Conclusion

References

9      Optical Coherence Tomography Angiography in Retinal Venous Occlusions

Mostafa Hanout, Paulo Ricardo Chaves de Oliveira, and Alan R. Berger

9.1    Introduction

9.2    Evaluation of the Fovea Avascular Zone

9.3    Macular Edema

9.4    Assessment of Retinal Perfusion and Vascular Abnormalities

9.5    Optic Nerve Head Evaluation

9.6    Conclusion

References

10    Optical Coherence Tomography Angiography and Central Serous Chorioretinopathy

Wasim A. Samara, Carl D. Regillo, and Allen C. Ho

10.1   Introduction

10.2   Acute Central Serous Chorioretinopathy

10.3   Chronic Central Serous Chorioretinopathy

References

11    Optical Coherence Tomography Angiography in Macular Telangiectasia Type 2

Alain Gaudric and Valérie Krivosic

11.1   Introduction Telangiectasia

11.2   Early Stage with Isolated Telangiectasia

11.3   Intermediate Stage with Outer Intraretinal New Vessels

11.4   Advanced Stage with Subretinal New Vessels and Fibrosis

11.5    Late Atrophic Stage

11.6    Conclusion

11.7    Disclosure

  References

12    Optical Coherence Tomography Angiography and Adult-Onset Foveomacular Vitelliform Dystrophy

Giuseppe Querques, Adriano Carnevali, Federico Corvi, Lea Querques, Eric Souied, and Francesco Bandello

12.1   Introduction

12.2   Conventional Multimodal Imaging

12.3   Optical Coherence Tomography Angiography

12.4   Conclusion

References

13    Optical Coherence Tomography Angiography and High Myopia

Taku Wakabayashi and Yasushi Ikuno

13.1   Introduction

13.2   Optical Coherence Tomography in High Myopia

13.3   Imaging Artifacts in High Myopia

13.4   Myopic Choroidal Neovascularization

13.5   Lacquer Cracks

13.6   Chorioretinal Atrophy

 Reference

14     Optical Coherence Tomography Angiography and Uveitis

 Eduardo A. Novais, André Romano, and Rubens Belfort Jr.

14.1   Introduction

14.2   Optical Coherence Tomography Angiography in Retinal Vasculitis

14.3   Optical Coherence Tomography Angiography in Chorioretinal Inflammations

14.3.1 White Dot Syndromes

14.3.2 OCT Angiography for Secondary Choroidal Neovascularization

14.4   Disadvantages of Optical Coherence Tomography Angiography in Uveitis

14.5   Conclusion

References

15    Optical Coherence Tomography Angiography Findings in Ocular Oncology and Radiation Retinopathy

Meghna V. Motiani, Colin A. McCannel, and Tara A. McCannel

15.1   Introduction

15.2   Posterior Segment Tumors

15.2.1 Retinal Tumors

15.2.2 Retinal Pigment Epithelial Tumors

15.2.3 Choroidal Tumors

15.3    Cancer Associated Ocular Vascular Complications

15.3.1 Radiation Treatment of Choroidal Tumors

15.3.2 Radiation Retinopathy

15.4    MEK-Inhibitor Maculopathy

15.5    Conclusion

References

16    Optical Coherence Tomography Angiography and Glaucoma

Gábor Holló

16.1   Why Use Optical Coherence Tomography Angiography for Disc Assessment in Glaucoma?

16.2   Determination of Disc and Peripapillary Vessel Density with Optical Coherence Tomography Angiography

16.3   Optical Coherence Tomography Angiography of the Healthy Disc

16.4   Comparison of Vessel Density between Healthy and End-Stage Glaucomatous Eyes

16.5   Diffuse Perfusion Damage and Retinal Nerve Fiber Loss in Advanced Glaucoma

16.6   Localized Perfusion Damage and Retinal Nerve Fiber Loss in Early Glaucoma

16.7   Discrimination of an Aneurysm from a Deep Disc Hemorrhage in Glaucoma Using Optical Coherence Tomography Angiography

16.8   Optical Coherence Tomography Angiography Signs of a True Disc Hemorrhage

16.9   Detection of Artifacts Resembling Perfusion Damage and Nerve Fiber Loss

16.10  Differential Diagnosis of Glaucoma Using Optical Coherence Tomography Angiography

16.11  The Future of Optical Coherence Tomography Angiography in Glaucoma Research and Clinics

16.12  Disclosure

 References

17    Optical Coherence Tomography Angiography and Anterior Segment Vasculature

Christophe Baudouin, Stephanie Hayek, and Adil El Maftouhi

17.1   Introduction

17.2   Principles of Optical Coherence Tomography Angiography for the Front of the Eye

17.3   Technical Issues

17.4   Optical Coherence Tomography Angiography in Corneal Diseases

17.5   OCTA for Conjunctival Vessel Assessment: Application in Glaucoma Surgery

17.6   Iris Vessels

17.7   Blood or Lymphatic Vessels?

17.8   Conclusion

References

18    The Future of Optical Coherence Tomography Angiography

Emily D. Cole, Eric M. Moult, Eduardo A. Novais, James G. Fujimoto, and Nadia K. Waheed

18.1   Spectral Domain and Swept-Source Optical Coherence Tomography

18.2   Advances in Optical Coherence Tomography Angiography Algorithms

18.3   Quantitative Analysis of Optical Coherence Tomography Angiography

18.4   Quantifying Ocular Blood Flow with Doppler Optical Coherence Tomography

18.5   Conclusion

References

19    Optical Coherence Tomography Angiography Rounds

David R. Chow

19.1    Case 1

19.2    Case 2

19.3    Case 3

19.4    Case 4

19.5    Case 5

19.6    Case 6

19.7    Case 7

19.8    Case 8

19.9    Case 9

19.10   Case 10

19.11   Case 11

    Index

Preface

Ophthalmologists are fortunate to be the recipient of great advances in technology. Over and over, we are presented with exciting new technologies to aid in the diagnosis of our patients and to treat our patients in the office or operating room. Without question one of the areas that will change the most over the next decade will be imaging technologies that will make the examining room of the 21st-century retina specialist a very technologically savvy thing! Optical coherence tomography (OCT) angiography will be one of the exciting new imaging technologies that will transform our office. It offers ophthalmologists the ability to image the vasculature of the retina and choroid in a noninvasive way using a technology and platform that is already integral and familiar to our offices. An OCTvolume scan can now be taken and split into “slabs” that can then be viewed to assess the functional vasculature at different layers of the retina and choroid. Even though it is a very immature technology, already great advances are being made in our understanding of retinal diseases due to its ability to provide insights into parts of the retinal circulation that were previously poorly imaged. Furthermore, recent advances in imaging resolution, image quality, and software algorithms for interpretation of images are forwarding the technology as a whole. This textbook includes many authors who are experts in this new imaging modality from all over the world. It covers the technology in a comprehensive manner with most of the chapters focusing on retinal diseases and a few focusing on expanding indications of this technology in glaucoma, the anterior segment, uveitis, and oncology. We hope you will find this textbook a valuable addition to your library, providing a current state-of-the-art look at the technology!

David R. Chow, MD, FRCSC

Contributors

Francesco Bandello, MD, FEBOOphthalmologistDepartment of OphthalmologyUniversity Vita-SaluteIRCCS Ospedale San RaffaeleMilan, Italy

Christophe Baudouin, MD, PhDProfessor and Chair of OphthalmologyQuinze-Vingts National Ophthalmology Hospital &Vision InstituteParis, France

Rubens Belfort Jr., MD, PhD, MBAHead ProfessorFederal University of São Paulo (UNIFESP)São Paulo, BrazilPresidentVision InstituteSão Paulo, Brazil

Alan R. Berger, MDCM, FRCSCVitreoretinal Surgeon, St. Michael's HospitalVice Chairman, Clinical ServicesDept. of Ophthalmology and Vision SciencesUniversity of TorontoToronto, Canada

Adriano Carnevali, MDDepartment of OphthalmologyUniversity Vita-SaluteIRCCS Ospedale San RaffaeleMilan, ItalyDepartment of OphthalmologyUniversity of “Magna Graecia”Catanzaro, Italy

David R. Chow, MD, FRCSCAssistant ProfessorDepartment of OphthalmologySt Michaels HospitalUniversity of TorontoFellowship Director and Co-DirectorToronto Retina InstituteToronto, Ontario, Canada

Emily D. Cole, BSNew England Eye CenterTufts University School of MedicineBoston, Massachusetts

Federico Corvi, MDDepartment of OphthalmologyUniversity Vita-SaluteIRCCS Ospedale San RaffaeleMilan, Italy

James G. Fujimoto, PhDElihu Thomson Professor of Electrical EngineeringMassachusetts Institute of TechnologyDepartment of Electrical Engineering and ComputerScience and Research Lab of ElectronicsCambridge, Massachusetts

Alain Gaudric, MDEmeritus ProfessorUniversité Paris-Diderot, Sorbonne Paris-CitéHôpital Lariboisiere, AP-HPParis, France

Mostafa Hanout, MD, MScClinical Fellow, Vitreoretinal SurgeryDepartment of Opthalmology and Visual SciencesUniversity of TorontoSt. Michael's HospitalToronto, Ontario, Canada

Stephanie Hayek, MDResidentQuinze-Vingts National Ophthalmology HospitalParis, France

Allen C. Ho, MDProfessor of OphthalmologyWills Eye Hospital Retina ServiceMid Atlantic RetinaThomas Jefferson UniversityPhiladelphia, Pennsylvania

Gábor Holló, MD, PhD, DScProfessor of OphthalmologyHead, Glaucoma and Perimetry UnitDepartment of Ophthalmology, Semmelweis University,BudapestBudapest, Hungary

Nicholas A. Iafe, MDOphthalmology ResidentStein Eye InstituteUniversity of California Los AngelesLos Angeles, California

Yasushi Ikuno, MDDirector and FounderIkuno Eye CenterInvited ProfessorGraduate School of MedicineOsaka UniversityClinical ProfessorGraduate School of Medical SciencesKanazawa UniversityOsaka, Japan

Peter K. Kaiser, MDChaney Family Endowed Chair in OphthalmologyResearchProfessor of OphthalmologyCleveland, Ohio

Keyvan Koushan, MD, FRCSCVitreoretinal SurgeonMt. Sinai HospitalUniversity of TorontoToronto, Ontario, Canada

Valérie Krivosic, MDHôpital Lariboisiere, AP-HPService d'OpthalmologieReference Center for Rare Vascular Diseases of Brainand Eye (CERVCO)Paris, France

Mark Lane, MDOpthalmologistUniversity Hospitals Birmingham NHS Foundation TrustBirmingham, United Kingdom

Ricardo Noguera Louzada, MDOpthalmologistDepartment of OphthalmologyFederal University of GoiásGoiânia, BrazilNew England Eye CenterTufts University School of MedicineBoston, Massachusetts

Adil El Maftouhi, ODCentre Ophtalmologique RabelaisLyon, France

André Correa Maia de Carvalho, MD, PhDRetina ClinicSão Paulo, BrazilDepartment of OphthalmologyFederal University of São Paulo (UNIFESP)School of MedicineSão Paulo, Brazil

Colin A. McCannel, MD, FACS, FRCSAssociate Professor of OphthalmologyCharles Drew UniversityVisiting Associate ProfessorStein Eye InstituteUniversity of California, Los AngelesLos Angeles, California

Tara A. McCannel, MD, PhDAssociate Clinical Professor of OphthalmologyDirectorOphthalmic Oncology CenterJules Stein Eye InstituteLos Angeles, CA, United States

Alexandra Miere, MDOpthalmologistDepartment of OphthalmologyCentre Hospitalier Intercommunal de Créteil (CHIC)Université Paris Est CréteilCréteil, France

Meghna Motiani, MDResident PhysicianCedars Sinai Medical CenterDepartment of Internal MedicineLos Angeles, California

Eric M. Moult, BScMassachusetts Institute of TechnologyDepartment of Electrical Engineering and ComputerScience and Research Lab of ElectronicsCambridge, Massachusetts

Eduardo A. Novais, MDRetina Specialist and PhD CandidateDepartment of OphthalmologyFederal University of São Paulo (UNIFESP)São Paulo, Brazil

Paulo Ricardo Chaves de Oliveira, MDOphthalmology degreeFaculdade de Ciências Médicas da Santa Casa de São PauloRetinal fellowshipRetina Clinic, São PauloUveitis fellowshipFederal University of São Paulo (UNIFESP)Retinal Research FellowToronto Retina Institute, CanadaRetinal specialistInstituto Panamericano da VisãoGoiânia, Brazil

Nopasak Phasukkijwatana, PhD, MDInternational Fellow in Medical RetinaStein Eye Institute, University of California Los AngelesLos Angeles, CaliforniaDepartment of OphthalmologyFaculty of Medicine Siriraj Hospital, Mahidol UniversityBangkok, Thailand

Giuseppe Querques, MD, PhDHead - Medical Retina & Imaging UnitDepartment of OphthalmologyUniversity Vita SaluteIRCCS Ospedale San RaffaeleMilan, Italy

Lea Querques, MDOphthalmologistDepartment of OphthalmologyUniversity Vita-SaluteIRCCS Ospedale San RaffaeleMilan, Italy

Carl D. Regillo, MDProfessor of OphthalmologyDirector of Wills Eye Hospital Retina ServiceMid Atlantic RetinaThomas Jefferson UniversityPhiladephia, Pennsylvania

André Romano, MDDirectorNeovista Eye InstituteSão Paulo, BrazilAdjunct ProfessorUniversity of MiamiMiller School of MedicineMiami, Florida

Wasim A. Samara, MDPostdoctoral Research FellowWills Eye Hospital Retina ServiceMid Atlantic RetinaThomas Jefferson UniversityPhiladelphia, PennsylvaniaDavid Sarraf, MDClinical Professor of OphthalmologyStein Eye InstituteUniversity of California Los AngelesLos Angeles, California

Abtin Shahlaee, MDPostdoctoral Research FellowWills Eye Hospital Retina ServiceMid Atlantic RetinaThomas Jefferson UniversityPhiladelphia, Pennsylvania

Sumit Sharma, MDAssistant ProfessorOphthalmologyCleveland Clinic Cole Eye InstituteCleveland, Ohio

Eric Souied, MD, PhDProfessor and HeadDepartment of OphthalmologyCentre Hospitalier Intercommunal de Créteil (CHIC)Université Paris Est CréteilCréteil, France

Nadia K. Waheed, MD, MPHAssociate Professor of OphthalmologyTufts University School of MedicineDirectorBoston Image Reading CenterTufts Medical Center/New England Eye CenterBoston Image Reading CenterNew England Eye CenterBoston, Massachusetts

Taku Wakabayashi, MDOphthalmologistDepartment of OphthalmologyOsaka University Graduate School of MedicineOsaka, Japan

1 Optical Coherence Tomography Angiography: Understanding the Basics

David R. Chow

Summary

Optical coherence tomography (OCT) angiography is an exciting new imaging modality that uses motion contrast to provide a noninvasive image of the retinal and choroidal vasculature. It is based on the acquisition of a three-dimensional (3D) volume OCT scan, which is then autosegmented and viewed en face to provide a view of the vasculature at any level of the retina or choroid. This chapter will review the basics of OCT angiography including the underlying technology, understanding the images obtained, and the evolving literature on these images in healthy eyes.

Keywords: optical coherence tomography angiography, fluorescein angiography, split spectrum amplitude decorrelation angiography, motion correction technology, autosegmentation

1.1 Introduction

Over the past 25 years, there has been a dramatic uptake in the usage of optical coherence tomography (OCT) as a noninvasive clinical tool to evaluate the structural anatomy of the macula and optic nerve head. Following its initial release as a research tool in the early 1990s, it reached mainstream clinical usage in the early 2000s with time domain technology, but really took off after 2005 with the release of Fourier domain or spectral domain OCT, which featured vast improvements in imaging resolution due to the higher scanning speeds coupled with motion correction technologies, such as eye tracking.1 Present-day clinical retina practice is characterized by a combination of a clinical exam, OCT imaging to evaluate the structural anatomy of the macula, fluorescein angiography (FA) to evaluate the retinal vasculature and identify sites of leakage or staining, and on occasion indocyanine green (ICG) angiography to better evaluate the deeper choroidal circulation. Practice patterns as defined by the graduating Retina Fellows at the Retina Fellow Forum have shown an increasing reliance on OCT imaging to define clinical activity and a reducing usage of FA in the diagnosis and management of retinal diseases ( ▶ Fig. 1.1, ▶ Fig. 1.2). Since 1961 when FA was first used to image the retinal vasculature, it has been the gold standard for evaluating the retinal vasculature and retinal conditions characterized by leakage or staining. Although the capabilities of FA are well known to all retina specialists, so too are its risks, related to the intravenous injection of a dye, which is associated with nausea, vomiting, and anaphylactic shock.2,​3,​4,​5 It also requires a significant investment in time, equipment, and well-trained personnel to perform properly.

Fig. 1.1 Decreasing utilization of fluorescein angiography on new patients with WET ARMD. ARMD, age-related macular degeneration.

(Data from graduating retina fellows at the North American Retina Fellow Forum, 2010–2015.)

Fig. 1.2 Decreasing utilization of fluorescein angiography for patients with WET ARMD on Anti-VEGF therapy. ARMD, age-related macular degeneration; VEGF, vascular endothelial growth factor.

(Data from graduating retina fellows at the North American Retina Fellow Forum, 2010-2015.)

1.2 So What Is Optical Coherence Tomography Angiography and Why Is It So Exciting?

Over the last few years, the advances in imaging speeds and resolution of OCT platforms have resulted in the ability to detect blood flow by motion contrast and by extension provide an en face view of the retinal vasculature. The underlying principle behind this is that sequential B-scans are taken of the SAME retinal location and then subjected to analysis to determine if there was any change in the amplitude or phase of the scan. If changes are detected, this signifies movement in the retinal tissue of this location ( ▶ Fig. 1.3). The movement is inferred to be due to the flow of red blood cells in the vasculature, although there are occasional artifacts that can create a “false” impression of movement of the retina. The obtained signal can then be amplified (ex SSADA—split spectrum amplitude decorrelation angiography) and digitally processed to provide an en face view of the vasculature at different layers of the retina. Various motion correction technologies are also typically applied to the data to further enhance the quality (signal-to-noise ratio) of the obtained images ( ▶ Fig. 1.4).6,​7,​8,​9,​10,​11,​12 The data are obtained in the typical manner that a structural OCT cube scan is done and in the same time sequence approximately 3 to 4 seconds. So, it importantly does not change the flow in a busy clinical retinal practice. Even better, and without question the most outstanding feature of OCT angiography (OCTA) is that this is all done without the injection of a contrast dye, so no intravenous (IV) and no risks of allergic reactions. OCTA is NONINVASIVE!

Fig. 1.3 Basic principle behind optical coherence tomography (OCT) angiography: sequential B-scans are taken of the retina at the exact same location. These scans are then compared to look for any changes in the signal. When present, this is deemed to represent movement in the retina at this location and inferred to represent blood flow. The deviation in the signal is mathematically assessed to provide a decorrelation signal representing the amount of blood flow at that point on the retina.

Fig. 1.4 Motion correction technology. (a) Horizontal priority fast transverse scans (Fast-X), (b) vertical priority fast transverse scans (Fast-Y) are taken, and then (c) software analyzed (Optovue’s AngioVue system 2015) and merged to create a better-quality image free of motion artifacts including residual axial motion and transverse saccadic motions.

1.3 Making Sense of the Information Obtained in an OCTA

As every OCTA obtained is essentially a cube scan, it is a three-dimensional (3D) assessment of the retinal vasculature unlike traditional fluorescein or ICG angiography, which is two dimensional. As a result, to properly evaluate the data, an approach has to be taken to make sense of the volume of information. One approach could be to evaluate the scans from the inner retinal surface right down to the choroid in a continuous manner. This could be done manually or by creating a movie file of the scans. Both of these options require significant physician time and as a result there would be reluctance to use the data in this manner. In an attempt to simplify the data, most commercially available OCTA machines have taken the cube and split it into slabs to reflect a known anatomic layer of the retinal vasculature, referred to as autosegmentation. For instance, the AngioVue software on the Optovue OCTA splits the volume cube up into the following four slabs:

Inner retinal slab extends from 3 µm below the internal limiting membrane to 15 µm below the inner plexiform layer. This incorporates the known anatomic location of the superficial retinal vascular plexus, which is generally what we see on traditional FA ( ▶ Fig. 1.5).

Middle retinal slab extends from 15 µm below the inner plexiform layer to 70 µm below the inner plexiform layer and incorporates the known location of the deep retinal capillary plexus. This plexus is poorly seen on traditional FA and beautifully seen on OCTA. Evaluating this region on OCTA is already providing insights into the pathology of conditions such as parafoveal telangiectasia (PFT) type 2b, paracentral acute middle maculopathy (PAMM), and retinal angiomatous proliferation (RAP), which we were unable to visualize clearly on traditional FA ( ▶ Fig. 1.6).

Outer retinal slab extends from 70 µm below the inner plexiform layer to 30 µm below the retinal pigment epithelium (RPE) reference line. This region anatomically corresponds to a part of the retina within which there is NEVER any vasculature in a normal individual. As a result, this slab should always be empty or blank unless there is pathology ( ▶ Fig. 1.7). This slab can be very useful to identify type 2 (subretinal) neovascular membranes.

Choriocapillaris extends from 30 µm below the RPE reference to 60 µm below the RPE reference. It incorporates the choriocapillaris and allows detection of early type 1 (sub-RPE) choroidal neovascular membranes (CNVM; ▶ Fig. 1.8).

Fig. 1.5 Inner retinal slab (Optovue’s AngioVue system) extends from 3 µ below the internal limiting membrane to 15 µ below the inner plexiform layer. (a) The optical coherence tomography (OCTA) image obtained looks very similar to the view obtained on traditional fluorescein angiography. (b) The traditional anatomic structure of the superficial retinal vascular plexus.

Fig. 1.6 Middle retinal slab (Optovue’s AngioVue system) extends from 15 µm below the inner plexiform layer to 70 µm below the inner plexiform layer. (a) The optical coherence tomography (OCTA) image shows the deep retinal vascular plexus in detail never seen on traditional fluorescein angiography. This view of the deep retinal plexus is one of the more powerful new capabilities of OCTA. (b) The traditional view of the anatomy of the deep retinal plexus.

Fig. 1.7 Outer retinal slab (Optovue’s AngioVue system) extends from 70 µm below the inner plexiform layer to 30 µm below the retinal pigment epithelium (RPE) reference line. (a) The optical coherence tomography (OCTA) image shows an empty box in normal individuals, as there is NEVER any vasculature in this part of a normal retina. (b) The anatomy of the slab imaged in the outer retinal slab.