How OCT innovations are changing glaucoma care
Optical coherence tomography (OCT) is swiftly improving the diagnosis of glaucoma, according to Joel S. Schuman, MD, who helped invent the technology.
“It’s the most rapidly adopted ophthalmic technology in history,” said Dr. Schuman, professor and chairman, Department of Ophthalmology, NYU Langone Medical Center, NY.
Already, OCT studies have yielded key insights into the relationships of retinal nerve fiber layer thinning and vessel density to visual field loss, Dr. Schuman said.
Delivering the Drs. Henry and Frederick Sutro Memorial Lecture at the 6th Annual Glaucoma 360 New Horizons Forum, Dr. Schuman recounted his role in the development of OCT and outlined some of its major findings.
He defined OCT as a form of optical biopsy—“the in situ imaging of tissue microstructure with a resolution approaching that of histology, but in real time, without the need for tissue excision and processing.”
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OCT uses near-infrared light in a Michelson-type interferometer. The underlying principle that made OCT possible is time gating, Dr. Schuman said, a system for isolating a portion of a time record for further viewing and analysis.
“Time gating removes unwanted scattered light and partially recovers the image,” Dr. Schuman explained. The low coherence allows high resolution.
During his fellowship, Dr. Schuman was working in the laser lab at Massachusetts Eye and Ear and became interested in the possibility of using optical coherence domain reflectometry (OCDR) which other researchers were using to measure the thickness of the cornea for refractive surgery. Dr. Schuman became interested in using it to measure the thickness of the retina in glaucoma and macular disease.
His supervisor at Massachusetts Eye and Ear was not interested, but allowed him to take the idea to Massachusetts Institute of Technology (MIT), where he began to collaborate with David Huang, then an MD-PhD student.
They cut calf eyes in half and looked at the back halves under OCDR to see if there was a signal. When they found that there was, Dr. Huang came up with the idea of moving the OCDR beam transversally to create a B-scan that could be interpolated with the original A-scan, creating a tomogram.