Retinal Diseases
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Over 260 OCT Images Optical Coherence Tomography in Retinal Diseases A Practical Interactive Book For Technicians And Retinal Clinicians Mariano Cozzi Alessandro Invernizzi Carlo Domenico Bianchi Supervised By: E. Priel - G. Staurenghi COPYRIGHT Mariano Cozzi Alessandro Invernizzi Carlo Domenico Bianchi i Main Authors Mariano Cozzi Alessandro Invernizzi Carlo Domenico Bianchi Contributors Alessandro Pagani Sergio Pagliarini Ethan Priel Supervisor Ethan Priel Giovanni Staurenghi Between flesh and what’s fantasy B. Springsteen ii AUTHORS AFFILIATIONS Mariano Cozzi Orthoptist/Research Ophthalmic Photographer, Eye Clinic, Department of Biomedical and Clinical Sciences "Luigi Sacco" Sacco Hospital, Univer- sity of Milan, Milano, Italy. Alessandro Invernizzi MD Ophthalmologist, medical retina and uveitis service, Eye Clinic, Depart- ment of Biomedical and Clinical Sciences "Luigi Sacco" Sacco Hospital, University of Milan, Milano, Italy. Carlo Domenico Bianchi Orthoptist, Eye Clinic, Department of Biomedical and Clinical Sciences "Luigi Sacco" Sacco Hospital, University of Milan, Milano, Italy. Alessandro Pagani Orthoptist, Eye Clinic, Department of Biomedical and Clinical Sciences "Luigi Sacco" Sacco Hospital, University of Milan, Milano, Italy. Sergio Pagliarini MD Ophthalmologist, Retinal Consultant, The Macular Unit, University Hos- pital Coventry and Warwickshire, Coventry, United Kingdom. Ethan Priel Director / Chief Ophthalmic Photographer, Ophthalmology Department, MOR, Bnei Brak, Israel. Giovanni Staurenghi MD Professor of Ophthalmology, Chairman Eye Clinic, Director Residency Program, Eye Clinic, Department of Biomedical and Clinical Sciences "Luigi Sacco" Sacco Hospital, University of Milan, Milano, Italy. iii ABBREVIATIONS AMD: age-related macular degeneration ICG: indocyanine green angiography ART: automatic real time ILM: inner limiting membrane INL: inner nuclear layer BM: Bruch’s membrane IPL: inner plexiform layer BRAO: branch retinal artery occlusion IR: infrared reflectance image BRVO: branch retinal vein occlusion IS/OS: inner segment/outer segment C: choroid MAC TEL: macular telangiectasia CC: choriocapillaris MC: multicolor image CNV: choroidal neovascularization CRAO: central retinal artery occlusion NFL: nerve fiber layer CRVO: central retinal vein occlusion CSCR: central serous chorioretinopathy OCT: optical coherence tomography CSJ: choroid scleral junction ONL: outer nuclear layer cSLO: confocal scanning laser ophthalmoscope OPL: outer plexiform layer EDI: enhanced depth imaging PCV: polypoidal choroidal vasculopathy ELM: external limiting membrane PED: pigment epithelium detachment ERM: epiretinal membrane RAP: retinal angiomatous proliferation FA: fluorescein angiography RF: red-free/blue reflectance image FAF: fundus autofluorescence RPE: retinal pigment epithelium FCE: focal choroidal excavation FP: color fundus photo SCL: sclera SD: spectral domain GCL: ganglion cells layer SRD: serous detachment of the neurosensory retina / sub retinal fluid TD: time domain HD: high definition HS: high speed VMA: vitreomacular adhesion VMT: vitreomacular traction iv INTRODUCTION Optical coherence tomography (OCT) is a recently introduced im- ages collected from the same patients with different instruments to aging technique which provides high resolution images of eye tis- better appreciate similarities and differences. sues sections. It signals a new era in the field of non-invasive diag- Finally we will present a large quantity of examples with B-scan nosis and in follow-up of several ophthalmological pathologies. OCT describing pathological findings and pathological conditions The revolution caused by these instruments is a result of their capa- most commonly founded in everyday OCT clinical practice. bility to study eye structures which are vitally important for vision, An assessment chapter with interactive quiz questions is available such as the optical nerve, the choroid, the retina and in particular at the end of the book. This is made up 80 scans each one includes the macula, in much greater detail than is possible with other meth- 4 multiple choices. An enjoyable way to learn and check your ods. knowledges. Since the OCT is mainly used for studying the macular region, this manual will essentially focus on the correct acquisition and inter- pretation of OCT images in this area of the retina. This is essential given the increasing use of OCT in daily clinical practice, and the differences existing between the several commer- cially available instruments. especially nowadays , when the lack of a common software and standard acquisition protocols creates difficulties while comparing images and measurements produced with different machines. Starting from these considerations the aim of this publication is to provide clinicians and technicians a practical support when using this fascinating imaging technique and to overcome the afore- mentioned difficulties with a thorough evaluation and compara- tive examination of different instruments An introduction to OCT methodology, its evolution and basic work- ing principles are presented in the first part of the manual. A com- parison between four OCTs models is presented by a series of im- v CHAPTER 1 Optical Coherence Tomography Alessandro Invernizzi, Mariano Cozzi, Carlo D. Bianchi, Alessandro Pagani 6 SECTION 1 A Brief History Optical Coherence Tomography publications per year 3462 3500 2958 3000 2673 2500 2275 1939 2000 1604 1500 1311 1135 1000 864 690 487 500 300 178 118 131 62 66 1 0 3 3 12 18 28 0 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Year 7 The use of optical interferometry was first described by Simonsohn lecting images beyond a certain resolution and make it vulnerable et al. in 1969.1 to moving artifacts, Following this, experiments to measure bulb length using interfero- However in the 2004 the introduction of a radically different tech- metry were carried out in the early 1980s. From this point on ad- nique for OCT signal analysis, the so called Spectral Domain vances in technology and further researches led to the develop- method, which will be analyzed in coming pages, generated a real ment of OCT in the early 1990s. revolution in the OCT world.6 The first in vivo images of eye tissue using OCT were published in This new technology drastically reduces image acquisition time re- 1993 by independent groups in Boston and Vienna.2-4 sulting in lower susceptibility to moving artifacts and in the crea- tion of scans with much higher resolution and quality. The first system available on the market was produced by Hum- phrey (Humphrey Instruments, Inc., San Leandro, California, USA Currently, Spectral Domain OCTs have supplanted the old Time in 1995 (OCT 1). Image acquisition was based on the so called Time Domain technology thank to the evident advantages they offer. De- Domain technology (OCT-TD) which will be discussed at greater spite this some clinical trials still require the use of Stratus OCT. length later. With this instruments the low resolution of the images Today there are several models available for purchase, produced made it impossible to distinguish fine anatomical detail. by the sector’s market leaders: Carl Zeiss Meditec, Heidelberg Engi- OCT using the same technology were became later available for neering, Nidek, OPKO, Optopol Technology, Optovue, Canon, Op- clinical practice, the most famous being the Stratus OCT (Carl tos, Tomey and Topcon Medical System. Zeiss Meditec, Inc., Dublin, California, USA). This machine made This has pushed producers towards healthy competition in devel- OCT extremely common and actually part of everyday clinical oping machines which are constantly improving. On the other practice. Nowadays, many years later, Stratus OCT can still be hand the existence of several instruments has been responsible for found in a large number of clinics worldwide. The images pro- difficulties in interpretation when comparing images. In fact, as we vided by this instrument allow a good view of retinal tissues associ- noted earlier, the lack of uniformity in image acquisition and analy- ated with a good repeatability so that was used in several clinical sis software often causes discordant results between different ma- trials for the evaluation of drugs and treatments for diabetic macu- chines and makes a definition of common guidelines more lar edema and age-related macular degeneration.5 difficult.7 This model of OCT dominated the market for approximately ten years with practically no competitors, although some technical limi- tations connected with scan acquisition speed, prevent it from col- 8 SECTION 2 Basic Working Principles Figure 1.1 Multiple A-Scans and B-Scans representation 9 From Signal to Image 8 A-scan A one-dimensional longitudinal scan that exploits the phenome- In this section we will examine some concepts frequently referred non of tissue reflectivity. For each A-scan reflectivity-versus-depth to during the course of the manual. These informations are needed curve is built up and then converted by software into a scale of in order to understand how light waves can give rise to retinal sec- false colors or shades of grey. tions similar to histological ones (tomograms). Like other imaging techniques such as ultrasound, OCT sends a wave beam through tissues and analyses the signal reflected back, transforming it into an image. However a single beam can only provide information about the portion of tissue it has travelled through; hence it will generate