Optical Coherence Tomography
Abstract
Optical Coherence Tomography (OCT) has matured in less than twenty-five years from a single A-scan taking more than 20 minutes to perform to a technology capable of imaging at more than 1,000,000 A-scans per second. It is the most broadly and rapidly adopted technology ever used in ophthalmology. There have been multiple technical advances since OCT’s introduction in 1991, including cross-sectional imaging of ocular tissues, segmentation of optical cross-sections into relevant tissue structures and layers, the advance to commercial time domain OCT (TD-OCT) at 400 A-scans per second, the introduction of normative OCT data, the advance from time domain to spectral domain OCT (SD-OCT), with commercially available SD-OCT at 25,000 to 64,000 A-scans per second, to ever faster imaging with swept source OCT (SS-OCT) and SD-OCT with ultra-fast cameras, with 3 dimensional OCT imaging and 3D image reconstruction. Laboratory work demonstrates even great potential in terms of image acquisition speed, as well as the capability for adaptive optics combined with OCT, spectroscopic OCT imaging, Doppler OCT, OCT oximetry, and multiple other potential applications. OCT in 2017 is faster, more reproducible and enables more detailed imaging than ever before.
OCT software allows clinicians to measure neural tissue in great detail, including the optic nerve, peripapillary retinal nerve fiber layer (RNFL), and the macular ganglion cell complex (GCC). These tissues can be segmented from OCT images and analyzed in three dimensions. Further, the measurements can be compared to normative data, allowing the discrimination between health and disease (in this case, glaucoma) and assessment of the degree of glaucomatous abnormality. Clinicians now have available to them software for assessing statistically significant change over time, allowing the evaluation of glaucoma progression.
The question that arises is, “How does statistically significant glaucomatous progression as detected by OCT relate to clinically significant glaucomatous change?” There is no easy answer to this question. It is possible to equate degree of RNFL abnormality (structural glaucoma damage) with the amount of visual field abnormality (functional glaucoma damage). It is clear that a dead or absent neuron cannot function, and that when enough neurons are lost this must correspond to lost visual field. Several studies have shown that progressive loss of RNFL as measured by OCT corresponds to progressive visual field loss, and further, that OCT detects more change events in a given period of time, and earlier change, than what is detectable by conventional standard achromatic perimetry. The relationship between OCT measured RNFL thinning and visual fields should be interpretable in the same context that visual field loss relates to clinically significant change in visual function. This parallelism may permit the understanding of OCT identified structural change and clinically significant glaucomatous change.
Bio
Joel S. Schuman, MD, FACS is Professor and Chairman of Ophthalmology at New York University Langone Medical Center, Professor of Electrical and Computer Engineering at the NYU Tandon School of Engineering, and Professor of Professor of Neuroscience and Physiology at the NYU Neuroscience Institute. Prior to arriving at NYU in 2016, he was Distinguished Professor and Chairman of Ophthalmology, Eye and Ear Foundation Endowed Chair in Ophthalmology, Director of UPMC Eye Center (2003-2016) and before that was at Tufts University in 1991, where he was Residency Director and Glaucoma and Cataract Service Chief. In 1998 he became Professor of Ophthalmology, and Vice Chair in 2001.
Dr. Schuman and his colleagues were first to identify a molecular marker for human glaucoma, published in Nature Medicine in 2001. Continuously funded by the National Eye Institute as a principal investigator since 1995, he is an inventor of optical coherence tomography (OCT), used world-wide for ocular diagnostics. Dr. Schuman published more than 300 peer-reviewed scientific journal articles.
In addition, in 2002 Dr. Schuman received the Alcon Research Institute Award and the Lewis Rudin Glaucoma Prize, in 2006 the ARVO Translational Research Award, and in 2012 the Carnegie Science Center Award as well as sharing the Champalimaud Award (a 1 million Euro cash prize). He was elected to the American Ophthalmological Society in 2008. In 2011 Dr. Schuman was the Clinician-Scientist Lecturer of the American Glaucoma Society. In 2013 he gave the Robert N. Shaffer Lecture at the American Academy of Ophthalmology (AAO) Annual Meeting, and received the AAO Lifetime Achievement Award. In 2014 he became a Gold Fellow of ARVO. He was elected to the American Association of Physicians in 2016. He is named in Who’s Who in America, Who’s Who in Medical Sciences Education, America’s Top Doctors and Best Doctors in America, and has been named a Top Doctor by Pittsburgh Magazine 2006–2016.