Summary
This is an introduction with a reader’s guide for our book on optical coherence tomography (OCT) for glaucoma. OCT is an invaluable tool for the diagnosis and management of glaucoma. This textbook provides a practical guide for the use of OCT in the clinical care of glaucoma patients: Including background on the development of OCT; in-depth descriptions of OCT of the optic nerve and retina in glaucoma patients, with chapters dedicated to illustrative case examples, artifacts, structure–function correlations, comparison of common devices, and anterior segment OCT; special considerations for OCT for childhood glaucomas and patients with high refractive errors; and future directions, namely, OCT angiography, swept-source OCT, and artificial intelligence. This introductory chapter also includes suggestions on how to use this guide depending on the reader’s background and interests.
Key words
optical coherence tomography – glaucoma – readers guide – optic nerve – retina – retinal nerve fiber layer1 Introduction: Practical Guide, OCT for Glaucoma
1.1 Introduction
Glaucoma is a group of eye diseases characterized by the loss of neural tissue at the optic nerve head, with “cupping” first visualized in the 1800s with Dr Helmholtz’ ophthalmoscope, and the associated loss of peripheral vision. Over the last several decades, advances in computerized imaging have enabled doctors to visualize and quantify the optic nerve tissue to an astounding degree. In the 2000s, optical coherence tomography (OCT) became an integral part of the care of glaucoma patients, from screening glaucoma suspects, to the diagnosis of glaucoma, and for following patients with glaucoma to assess for progression of the disease.
The purpose of this guide is to serve as both a reference for understanding how OCT is used for the diagnosis and treatment of glaucoma, as well as a practical guide for “everyday” use to help doctors use this technology with greater skill and confidence.
1.2 Overview of the Guide
Summaries of each chapter provide an overview of the guide.
1.2.1 Development of OCT
OCT is a now a fixture in eye clinics around the world but only came to exist less than 30 years ago. Following decades of research on how evolving laser technologies could have clinical applications, in 1991 the first OCT captured an image of the eye. The history of OCT captured an research and development is discussed by summarizing the science, sharing insights on the economic risks and successes, and highlighting clinical impacts. 1
1.2.2 OCT of the Optic Nerve
Assessing the optic nerve is critical in the evaluation of glaucoma patients. Computerized imaging technologies such as OCT provide quantitative measurements of optic nerve head parameters, including the retinal nerve fiber layer (RNFL). A systematic approach to OCT interpretation is discussed, including attention to potential limitations and artifacts. 2
1.2.3 OCT of the Macula
Retinal imaging of the macula, with attention to the retinal ganglion cell layer, inner plexiform layer, and nerve fiber layer, can supplement the information obtained with the peripapillary RNFL. Applications of macular imaging for glaucoma, advantages and disadvantages, and pitfalls to avoid are discussed. 3
1.2.4 Illustrative Case Examples
Case examples illustrate the use of OCT in glaucoma diagnosis and management. Cases spanning the spectrum of glaucoma severity are discussed, from glaucoma suspect, early to advanced glaucoma, as well as examples of glaucomatous progression. Characteristic findings from other chapters (3, 4, 6, and 7 in particular) are reinforced. 4
1.2.5 Structure–Function Relationship
The relationship between structure and function of the optic nerve is the basis of our pathophysiological understanding of glaucoma. This chapter describes structure–function mapping, the temporal relationship between structural damage and functional defects, and how structural changes are linked to functional changes in glaucoma. 5
1.2.6 Comparison of Common Devices
OCT devices produced by several manufacturers are available for clinical use. Differences in imaging specifications, analysis techniques, normative databases, and diagnostic capabilities are discussed for the Cirrus 6000 (Carl Zeiss Meditec AG, Jena, Germany), Spectralis (Heidelberg Engineering GmbH, Heidelberg, Germany), Avanti RTVue XR (Optovue, Inc., Fremont, CA, USA), and 3D OCT (Topcon Corporation, Tokyo, Japan). 6
1.2.7 Artifacts and Masqueraders
All OCT machines have artifacts. Critical assessment for artifacts and attention to ocular pathology unrelated to glaucoma are discussed, with relevant clinical examples of “red” and “green” “OCT diseases” and future directions. 7
1.2.8 Anterior Segment OCT in Glaucoma
OCT of the anterior segment provides noninvasive, high-resolution, cross-sectional images of the anterior segment structures. This technology can provide a useful supplement for the diagnosis and management of glaucomas, particularly primary angle closure disease. 8
1.2.9 Special Considerations: OCT in Childhood Glaucoma
OCT is an important tool for the management of childhood glaucoma, especially since children with glaucoma may not be able to perform visual field testing. Special considerations for the use of OCT in children are discussed, including how to acquire OCT images and suggestions for interpreting OCT images from pediatric eyes. 9
1.2.10 Special Considerations: High Refractive Errors
Special care should be taken when interpreting OCT scans in eyes with high refractive errors, given the rising prevalence of myopia and that myopia is a risk factor for glaucoma. Causes of OCT scan errors are discussed as well as newer parameters to improve the accuracy of glaucoma diagnosis in myopic eyes. 10
1.2.11 Future Directions: OCT Angiography for Glaucoma
OCT angiography is an emerging technology giving detailed images of the microvasculature of the optic nerve and retina. Although its role in the diagnosis and management of glaucoma is still unclear, growing evidence shows good correlation between OCT angiography of the optic nerve and surrounding structures, and tissue loss and visual field loss from glaucoma. 11
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