Atlas of Ocular Optical Coherence Tomography

486 Pages·2018·114.31 MB·English

by  Fedra Hajizadeh (eds.)

Fedra Hajizadeh Editor
Atlas of Ocular
Optical Coherence
Tomography
123
Atlas of Ocular Optical Coherence Tomography
Fedra Hajizadeh
Editor
Atlas of Ocular Optical
Coherence Tomography
Editor
Fedra Hajizadeh
Noor Eye Hospital
Tehran, Iran
ISBN 978-3-319-66756-0 ISBN 978-3-319-66757-7 (eBook)
https://doi.org/10.1007/978-3-319-66757-7
Library of Congress Control Number: 2017960826
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Dedicate to
my father, the greatest inspiring in my life,
my mother who graced my world with her unconditional love,
my children, Bamdad and Taraneh who gave me the chance of experiencing a
magical kind of love,
my sisters for kindness in their hearts and fire in their souls,
And to every person who has ever filled my heart with love,
…….and also to all wonderful readers of the book.
Foreword
The textbook Atlas of Ocular Optical Coherence Tomography, edited by Fedra Hajizadeh is a
monumental achievement and should serve as an incredibly important and valuable reference
tool for anyone with an interest in optical coherence tomography (OCT) and its most important
clinical applications. This text should be in particular invaluable to ophthalmology residents,
retina fellows, and general ophthalmologists who are increasingly called upon to have a sophis-
ticated understanding of OCT and its interpretation. OCT has truly transformed ophthalmol-
ogy and is an integral and indispensable tool in our care of patients with eye disease. As with
any diagnostic technology, its usefulness is ultimately limited by the interpretation skill of the
user. This OCT atlas should provide immediate dividends in improving one’s proficiency in
accurately interpreting OCT findings.
The text is comprehensive in its coverage, first providing an overview of OCT technology
and its limitations, and then sequentially reviewing OCT findings and interpretations in various
diseases including age-related macular degeneration, retinal vascular disorders, central serous
chorioretinopathy, vitreo-macular interface disorders, optic nerve diseases, tumors, pathologic
myopia, hereditary disorders, and inflammatory diseases. Although the focus of this text is
clearly the posterior segment, a very useful and important chapter is included on anterior seg-
ment OCT, a current hot topic in imaging.
The text is impeccably written and beautifully illustrated throughout and reflects the tre-
mendous expertize of Dr. Hajizadeh and her exceptional collaborators. There are over 600
images which illustrate the diversity of imaging findings that we encounter in clinical practice.
The images are not limited to OCT and include companion color, infrared reflectance, auto-
fluorescence, and angiographic images which allow the user to appreciate the importance of
multimodal imaging in making accurate disease diagnoses. The images are extensively anno-
tated and the legends are detailed, providing the reader with an exceptionally clear understand-
ing of the key features in each case.
In summary, this impressive atlas of OCT should serve as a key resource and reference for
ophthalmologists for many years to come.
Srinivas R. Sadda, M.D.
vii
Contents
1 Introduction to Optical Coherence Tomography . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Fedra Hajizadeh and Rahele Kafieh
2 Age Related Macular Degeneration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Ramak Roohipoor, Fatemeh Bazvand, Hassan Khojasteh, and Fedra Hajizadeh
3 Diabetic Retinopathy and Retinal Vascular Diseases . . . . . . . . . . . . . . . . . . . . . . 97
Nazanin Ebrahimiadib, Kevin Ferenchak, and Fedra Hajizadeh
4 Central Serous Chorioretinopathy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
Ramak Roohipoor, Fatemeh Bazvand, Mohammad Zarei, and Fedra Hajizadeh
5 Epiretinal Membrane, Macular Hole and Vitreomacular Traction
(VMT) Syndrome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
Fatemeh Bazvand, Ramak Roohipoor, and Fedra Hajizadeh
6 Optic Disc Anomaly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
Fedra Hajizadeh
7 Ocular Tumors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
Nazanin Ebrahimiadib and Fedra Hajizadeh
8 Pathologic Myopia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315
Fedra Hajizadeh
9 Hereditary Disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
Fedra Hajizadeh
10 Uveitis and Intraocular Inflammation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
Nazanin Ebrahimiadib, Fedra Hajizadeh, and Charles Stephen Foster
11 Anterior Segment Optical Coherence Tomography (AS-OCT) . . . . . . . . . . . . . . 417
Hassan Hashemi, Kazem Amanzadeh, and Fedra Hajizadeh
12 Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431
Fedra Hajizadeh
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 479
ix
Introduction to Optical Coherence 1
Tomography
Fedra Hajizadeh and Rahele Kafieh
Abstract
(1) Basics and principles of optical coherence tomography (OCT), which briefly discuss the
mechanisms and operation of OCT systems and a comparison of old and new systems (time
domain vs. spectral domain) and their reproducibility. It concisely explains the swept-
source OCT mechanism and OCT angiography as well. (2) Normal OCT, which describes
normal findings and variations that are expected on normal OCT images, and the layers of
the normal retina and in different parts of the posterior segment. (3) Enhanced-depth imag-
ing (EDI)-OCT and its applications and indications in various diseases such as choroidal
tumors, age-related macular degeneration, diabetic retinopathy, central serous chorioreti-
nopathy, glaucoma, intraocular inflammation, and myopia. Moreover, choroidal measure-
ment and its variations under different conditions are discussed. (4) Limitations and
indications of OCT, which evaluate and explain the drawbacks and advantages of this diag-
nostic method for the exploration of ocular pathologies. (5) Pitfalls and artifacts, which
covers and illustrates diagnostic pitfalls and artifacts in OCT image interpretation in cir-
cumstances such as the presence of an epiretinal membrane and myopia.
1.1 Basic Principles of Optical Coherence to ultrasound, each A-scan signal is acquired through axial
Tomography reflectance from various layers of an object. The location of
internal layers can be determined by using the signal-echo
1.1.1 Introduction to Optical Coherence delay times of each structure. The collection of cross-
Tomography sectional A-scans creates the B-scan or cross-sectional
image. Unlike in ultrasound imaging, there is no need for
Optical coherence tomography (OCT) is a recently devel- direct contact with the eye to transmit or receive light sig-
oped imaging method that depicts cross-sectional informa- nals. In addition, higher spatial resolution can be achieved
tion about an object. The basic performance of this method by using light instead of ultrasound waves [1]. Optical
is similar to that of ultrasound image acquisition, except that coherence tomography achieves a resolution of a few
OCT uses light beams in place of sound profiles. Comparable micrometers by using different light resources such as super
luminescent diodes, ultrashort-pulsed lasers, or supercon-
tinuum lasers. This method can have many applications in
F. Hajizadeh, M.D. (*)
Noor Ophthalmology Research Center, Noor Eye Hospital, the imaging of anatomical structures. Information concern-
No. 96, Esfandiar Blvd., Vali’asr Ave, Tehran, Iran ing the internal layers of medical structures is of interest to
e-mail: [email protected]
scientists. An important feature of an imaged object is the
R. Kafieh maximum allowable depth of 1–2 mm for which OCT is
Medical Image and Signal Processing Research Center, School of
applicable. At greater depths, the scattered beam will be too
Advanced Technologies in Medicine, Isfahan University of
weak to be processed for image reconstruction. Figure 1.1
Medical Sciences, Isfahan, Iran
e-mail: [email protected] depicts a block-diagram of this imaging technique.
© Springer International Publishing AG 2018 1
F. Hajizadeh (ed.), Atlas of Ocular Optical Coherence Tomography, https://doi.org/10.1007/978-3-319-66757-7_1
2 F. Hajizadeh and R. Kafieh
Fig. 1.1 Block diagram of
optical coherence
tomography. FFT fast Fourier Interferometer time
transform, OCT optical (Detector)
coherence tomography
+
Sample Reflection
time
Layers
Partial mirror FFT
Swept
Source λ
Reference Mirror OCT A-Scan Signal
1.1.2 Principles of Optical Coherence For two partially coherent beams, the interference is
Tomography achieved by the formula
In vivo OCT imaging of the anterior section of the eye with I =k1Is+k2Is+2 (k1Is).(k1Is).Reéëg(t)ùû (1.1)
approximately 10-μm resolution was first reported in 1994 [2]. in which I is the source intensity, and k + k < 1 is the
s 1 2
Working with two different teams, Hee and colleagues [2, 3] splitting ratio of the interferometer, and γ(τ) is the degree
introduced OCT of the human retina to discriminate between of coherence (i.e., the complex degree of coherence). The
different layers of the retina, morphological content of the fovea interference envelop depends on the time delay τ in signal
and optic disc, and thickness of the retinal nerve fiber layer. achievement (i.e., the desired variable in OCT). Because of
the gating issue in OCT, the complex degree of coherence
1.1.2.1 Time Domain OCT is usually represented by a Gaussian model:
Optical coherence tomography uses interferometry in low-
coherence or white light and creates cross-sectional images by é æ pDnt ö2ù
using the difference between the reflected light from a biologi- g(t)=expëêê-èç2 ln2ø÷ ûúú.exp(-j2pn0t) (1.2)
cal tissue and the reference light beam. The incident light
encountering a tissue may be scattered, transmitted, or absorbed. in which Δν is the spectral bandwidth of the source in the
According to principles of interferometry, the light from a frequency domain, and ν is the spectral bandwidth of the
light source reaches a beam splitter and is divided into two source in the frequency domain, and ν0 is the central frequency
parts. One beam is the reference beam and the other beam of the source. In Eq. 1.2, an optical carrier modulates the enve-
passes through the imaged structure. Different boundaries lope of the amplitude and the peak of the envelope for this
inside the structure reflect this beam and the echo beams modulation is placed at the desired distance from the object;
backscatter from each layer at different axial distances. At its peak corresponds to surface reflectivity. Based on the
the same time this process is occurring, the reference beam is Doppler phenomenon caused by the moving arm, an optical
reflected from a mirror placed at a specific distance. The two carrier would result. The frequency of the carrier is directly
beams are then combined again by an optical beam splitter correlated with the speed of movement in the arm. Therefore,
and are sent to an optical detector. When the two beams two functions can be defined for the moving arm: (1) depth
match, constructive interference occurs. scanning and (2) optical carrier with Doppler shift. In OCT,
In time domain OCT (TD-OCT), the aforementioned ref- the frequency of the aforementioned optical carrier can be cal-
erence arm should be positioned mechanically to determine culated by the formula
the matched distance. Based on the autocorrelation property
2.u .u
in a symmetric and low-coherence interferometer, the high- f = 0 s (1.3)
est value of the envelope of this modulation can occur with Dopp c
matched path lengths.
1 Introduction to Optical Coherence Tomography 3
in which υ0 is the central frequency of the source, υs is the Fourier transform. The optical setup is easier than the previous
movement speed of the arm, and c is the speed of light. method and the SNR increases. However, the nonlinear wave-
Furthermore, the axial resolution of OCT is defined by the length and high sensitivity are disadvantages of this strategy.
formula:
1.1.2.3 Image Construction
2ln2 l 2 l 2
l = . 0 »0.44. 0 (1.4) B-scans can be obtained by consecutive axial scans at cross-
c p Dl Dl wise locations [1]. In most OCT images, the intensity of the
backscattered signal is represented by false colors, in which
1.1.2.2 Frequency Domain OCT white and red represent the highest intensity reflection and
In frequency domain OCT, the movement of the arm is elimi- blue and black represent the lowest intensity.
nated and, because of Fourier transform, depth information
can be retrieved (Fig. 1.1). In such systems, the speed is 1.1.2.4 Reproducibility
improved to more than 25,000 axial scans per second. This is The reproducibility between time domain OCT and fre-
faster than time domain detection [4]. Frequency domain quency domain OCT has been compared in many studies
OCT can be categorized into two subclasses: (1) spatially [5–7], and intraclass correlation coefficients have been used
encoded and (2) time-encoded. to measure interscan reproducibility. Both imaging methods
In spatially encoded frequency domain OCT (also called show a high degree of reproducibility.
spectral domain OCT or Fourier domain OCT), the informa-
tion can be retrieved by spreading different optical frequen-
1.1.2.5 Optical Coherence Tomography
cies on an array of detectors. Therefore, a single exposure
Angiography
would be sufficient to acquire the needed whole frequencies.
Optical coherence tomography angiography is a novel imag-
However, the signal-to-noise (SNR) ratio is low because of
ing technique that is a noninvasive method that produces
the lower dynamic range of banding detectors, compared to
angiographic images without using dye. This method
that of single photosensitive diodes. Furthermore, the array
acquires many B-scans from the same position and compares
of detectors does not distribute the frequency of the light
them to produce a map from blood flow. Sequential imaging
equally on the detectors, which can also reduce the signal to
from the same location requires a very high imaging speed to
noise ratio (SNR) in the reconstruction stage.
provide approximately 6 s for the construction of each three-
In time encoded frequency domain OCT (also called swept-
dimensional (3D) scan set. The viewer can scroll among the
source OCT), the information encoding is not based on fre-
projection images (i.e., OCT angiograms) from the internal
quencies; the time separation is instead replaced. The spectrum
limiting membrane (ILM) to the choroid and view retinal
is generated in single frequencies and reconstructed before the
structures [8].