Swept-Source Optical Coherence Tomography

The following sections are included:

• LIST OF CONTRIBUTORS AND EDITORS
• ACKNOWLEDGMENTS
• FOREWORD
• CONTENTS

Optical coherence tomography (OCT) is an in vivo non-invasive patient friendly modality for visualizing ocular structures. It produces high resolution, cross-sectional images of posterior segment structures, akin to an optical biopsy…

Optical coherence tomography angiography (OCT-A) is a dye free, non-invasive method of visualizing the microvasculature of the retina in three dimensions. The principle behind OCT-A technology is based on the detection of differences in either amplitude, phase variance or intensity between serial B scans performed at the same location on the retina. These multiple scans are registered and the degree of decorrelation in signal is calculated and displayed graphically. Stationary tissue produces a nearly constant reflection on OCT, whereas moving tissue produces signals that change over time. Pixels from stationary non-changing structures are displayed as black and those pixels which show changes or fluctuations are displayed as bright. When scans across several regions are combined, a three-dimensional data set is obtained and various algorithms such calculation of speckled variance, split-spectrum amplitude decorrelation angiography (SSADA) and the optical micro-angiography (OMAG) algorithm can be applied to reconstruct enface angiograms of the retina…

The following sections are included:

• Macroaneurysm
• Idiopathic Macular Telangiectasia
• Retinal Vein Occlusion
• Diabetic Retinopathy
• References

Central serous chorioretinopathy (CSCR) is a disease characterized by choroidal hyperpermeability and leakage of fluid through the retinal pigment epithelium. Fluid accumulation results in neurosensory retinal detachment and/or retinal pigment epithelium detachment.

Age-related macular degeneration (AMD) is one of the main causes of visual impairment in individuals over the age of 50 years. Neovascular AMD (nAMD) or exudative AMD is an advanced form of AMD and is the leading cause of acute visual loss related to AMD. Choroidal neovascularization (CNV) is the hallmark of nAMD and can include features like hemorrhage, fluid exudation, fibrosis and photoreceptor damage which ultimately leads to vision loss. Treatment for this condition is with the use of anti-vascular endothelial growth factor (anti-VEGF) agents.

AMD CNV is traditionally diagnosed on dye-based angiography such as fluorescein or indocyanine green (ICGA). Optical coherence tomography (OCT) is also an important structural imaging modality which can help with the diagnosis and monitoring of response to treatment. The evaluation of AMD CNV is one of the most important applications of OCT-A. While it has not superseded dyebased angiographic techniques, it holds great promise as a noninvasive tool to diagnose AMD CNV and to assess its morphology and response to anti-VEGF therapy.

PCV is a subtype of AMD CNV characterized by polypoidal lesions arising from terminal dilatations with branching vascular networks (BVN) arising from the choroid. It has specific characteristic on clinical examination and on cross section OCT; however, diagnosis is made on indocyanine green angiography (ICGA). This subtype is clinically important as previous studies have suggested poorer response to anti-VEGF monotherapy and the condition may benefit from combination therapy with photodynamic therapy (PDT). It also affects a younger age group as compared to typical nAMD and is more common in the Asian population. The use of OCT-A imaging for PCV is shown to detect the BVN in the large majority of cases; however, it can only image 15–30% of the polypoidal structures. This is thought to be due to the unusual blood flow inside the polypoidal lesions.

The following sections are included:

• Epiretinal Membrane
• Macular Hole
• Vitreomacular Traction (VMT)
• References

Pathologic myopia is defined as a myopic refractive error of more than 6 dioptres or axial length >26.5 mm with associated degenerative changes of the fundus…

The following sections are included:

• Vogt-Koyanagi-Harada (VKH) Syndrome
• Punctate Inner Choroidopathy (PIC)
• Choroidal Hemangioma
• Choroidal Nevus
• Choroidal Metastases
• Focal Choroidal Excavation (FCE)
• Morning Glory Disc
• Choroidal Rupture

Optical coherence tomography angiography (OCT-A) has recently gained growing interest in exploring the optic nerve microvasculature in various optic nerve conditions, such as primary open angle glaucoma (POAG), and in other neuro-ophthalmic conditions, including optic atrophy, as well as ischemic, inflammatory, hereditary optic neuropathies. In POAG, OCT-A discloses localized attenuation of the optic nerve microvasculature, correlating with the disease severity and the associated visual field loss. In non-arteritic ischemic optic neuropathy, due to hypoperfusion in the capillary bed of the optic nerve head, OCT-A imaging may reveal segmental and global reduction of the peripapillary vascular flow density and peripapillary vascular tortuosity. Systemic conditions, like multiple sclerosis, can be associated with reduced vascular flow explored with OCT-A, even in the absence of optic neurities. Further prospective studies are needed to determine the specificity of these OCT-A findings and whether they constitute the cause or the consequence of the underlying condition.

The following section is included:

• INDEX