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International panel adopts consensus nomenclature for OCT imaging
Panel advocates standardized lexicon for future OCT research studies, including naming 18 ‘zones’ reflecting the layers of the retina.
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A panel of international retina specialists has proposed and adopted a standardized nomenclature for the classification of retinal and choroidal layers and bands visible on spectral-domain optical coherence tomography images of a normal eye.
“There have been numerous terms used for each structure seen in optical coherence tomography images. Some of these designations made sense; some were contradictory from one paper to another, even from the same research group,” co-author Richard F. Spaide, MD, a partner at Vitreous-Retina-Macula Consultants of New York, said.
Richard F. Spaide
“We can see or perceive structures based on some variation in optical character. This may mean a local change in refractive index or with microscopy the ability to retain or bind dyes or stains,” he said. “A structure that may show a high affinity for a histologic stain may not be particularly reflective in the infrared domain, which is where the range of wavelengths resides when we use OCT. Some structures are highly reflective because of their architectural arrangement of many layers of refractive index change, even though the absolute difference in change at any one interface is not that great.”
Spaide told Ocular Surgery News that structures seen clearly with one modality may not be the same structures that are readily apparent with other modalities.
“For example, one prominent structure in light microscopy of the retina is the outer nuclear layer because many common stains avidly bind to nuclei, thus the name,” he said. “As it turns out, this same layer shows almost no reflectivity in OCT and so appears as a featureless hyporeflective band.”
Bands and zones
The panel, officially known as International Nomenclature for Optical Coherence Tomography (IN•OCT), has met only once, 2 years ago in Venice, Italy. Since then, the writing committee has devoted considerable time to drafting a consensus nomenclature, including expanding on the term “zone” by naming 18 different zones in numerical order, progressing from the innermost to the outermost OCT-determined layers of the retina.
“With low-resolution time-domain OCT, groups of researchers identified reflections and immediately jumped to the idea that an anatomic structure produced those reflections,” Spaide said. “In several instances, though, what they assumed to be the anatomic source of a particular reflection probably was not. However, with the advent of improved imaging over the subsequent years, many additional structures and bands became visible. In some circumstances, the name given to one band in time-domain OCT was determined to be one band among other bands in SD-OCT.”
In order for a selected structure to be the lead candidate for a band name by the panel, the structure had to have biologic and physical characteristic relevance.
Spaide said it is likely that as OCT resolution continues to improve, so too will the ability to see things that are currently not visible.
“Since we do not have absolute proof of specific anatomic correlation to all of the reflective bands, and because there are likely to be subdivisions of bands we now know, the band was named for the zone of lead anatomic candidate,” he said. “That is as far as available evidence allows us to proceed.”
Lexicon creation
Spaide said the process of creating a proposed lexicon was “remarkably smooth,” once the framework of using available scientific evidence was embraced by the panel, along with an understanding that definitive layer assignments to specific anatomic features may not be possible and, thus, the term “zones” should be used. Spaide noted that Giovanni Staurenghi, MD, a professor of ophthalmology at the University of Milan, Italy, and lead author of the Ophthalmology article, compiled and organized images for review by the committee and initially polled the members for names of structures seen in the retina. This started the panel members thinking about the various layers, Spaide said. At the beginning of the meeting, a tally of these layers was presented. Many names were used for each layer, and this helped supply impetus to come up with one specific name for each layer.
Spaide said it is important for everyone to speak the same language and for the ophthalmic community to think in mechanistic terms.
“If we ascribe a name to a structure, then in disease states if we see abnormalities in an image involving that structure, we think the structure probably is involved in disease,” he said. “If we have the wrong name, then for groups of diseases we will come to the wrong conclusion as to the pathophysiology.”
Spaide also said, “Any naming convention is really a theory. Theories produce testable hypotheses. We can test hypotheses concerning specific bands or zones. If we confirm the theory, then great, we can have more confidence.”
Conversely, refuting part of the theory “is also great because we can improve the current theory. So a statement of nomenclature is really a start of a road map to progress.”
Spaide believes the establishment of a nomenclature system is on par with landmark meetings that produced influential comprehensive systemic examinations of disease, such as the Airlie House classification of diabetic retinopathy. – by Bob Kronemyer
Reference:
Staurenghi G, et al. Ophthalmology. 2014;doi:10.1016/j.ophtha.2014.02.023.For more information:
Richard F. Spaide, MD, can be reached at Vitreous-Retina-Macula Consultants of New York, 460 Park Ave., 5th Floor, New York, NY 10022; 212-861-9797; email: rickspaide@gmail.com.Disclosure: Spaide has no relevant financial disclosures.