Eyeworld

EW GLAUCOMA 54 by Michelle Dalton EyeWorld Contributing Writer Swept-source OCT and glaucoma F irst there was time-domain optical coherence tomogra- phy (TD-OCT), then spectral-domain OCT (SD-OCT); now a newer technology—swept-source OCT— may be able to image structures that the previous technologies could not, according to researchers involved in clinical studies of the device. "With swept-source technology, a frequency swept light source and a high speed detector are used to detect the interference signal as a function of time, instead of a spec- trometer and camera as in spectral- domain technology," explained James G. Fujimoto, PhD, Elihu Thomson Professor of Electrical Engineering and Computer Science, Massachusetts Institute of Technol- ogy, Cambridge. "The light source emits different frequencies sequentially and is ac- quired at a very rapid speed. Also, the average wavelength is longer than SD-OCT. The premise is that you get deeper penetration into the tissue without the shadowing arti- facts from overlying blood vessels like you do with SD-OCT," said Lucy Q. Shen, MD, Massachusetts Eye and Ear Infirmary, Boston, and instructor in ophthalmology, Harvard Medical School, Boston. Both swept-source and SD-OCT detect A-scans in the Fourier domain and have superior sensitivity com- pared to TD-OCT, Dr. Fujimoto said, adding that swept-source has less sensitivity roll off with range, and therefore the imaging range is longer than in SD-OCT. Dr. Fujimoto's group developed a prototype instrument in 2010 that uses swept-source OCT at long wavelengths of 1050 nm "to achieve imaging speeds of 100,000 A-scans per second and improved image penetration," he said. The Casia SS-1000 (Tomey, Nagoya, Japan) is a Fourier-domain, swept-source OCT designed specifi- cally for imaging the anterior seg- ment; the device performs 30,000 A-scans per second, allowing diag- nosticians to image 360 degrees around the anterior segment in 2.4 seconds. The Topcon Deep Range Imag- ing (DRI) OCT-1 Atlantis 3D SS OCT (Topcon Medical Systems, Oakland, N.J.) performs retinal imaging at 100,000 A-scans per second. Recently, however, Dr. Fujimoto's group has developed "an even higher performance swept- source OCT that can perform high speed retinal, anterior, and full eye length imaging," he said. "The newest swept-source OCT has the advantage that the light source fre- quency sweep range and repetition rate can be adjusted to tailor the resolution, imaging range, and axial scan repetition rate for the specific imaging application," Dr. Fujimoto and colleagues wrote. 1 In the group's latest prototype, vertical-cavity surface emitting laser (VCSEL) technology is used to en- able 3D OCT imaging spanning the February 2011 April 2014 have a role in glaucoma diagnosis, according to the literature A technology being investi- gated for use in posterior segment imaging may An example of the type of image that can be acquired with the Deep Range Imaging OCT-1 Atlantis Source: Topcon Device focus

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