Reviews Supplements Topcon 2014 : Page 1

Clinical Advantages of Swept-Source OCT and New Non-Damaging Laser Treatments Three leading surgeons offer their insight and experience on imaging with optical coherence tomography as well as laser treatment options. New Swept-Source OCT for Glaucoma: Improvements and Advantages A look at how this third-generation OCT differs from conventional OCT. Andrew J. Tatham, FRCOphth, FEBO hen we refer to swept-source optical coher-ence tomography (SS-OCT), “swept source” refers to the type of laser incorporated into the device. Instead of the superluminescent diode laser typical of conventional spectral domain OCT (SD-OCT), SS-OCT uses a short-cavity swept laser. Although the swept-source laser has a wavelength centered at approximately 1 µ m, the laser actually changes, because it sweeps across a narrow band of wavelengths with each scan. Like SD-OCT, SS-OCT has a fi xed ref-erence arm, but it does not use a spectrometer. Instead, a comple-mentary metal oxide semiconduc-tor camera is employed, along with two fast parallel photodiode detectors. The result is that SS-OCT is able to achieve the highest imaging speed of any commer-cially available OCT with 100,000 A-scans obtained per second. W Additionally, SS-OCT has a high axial resolution of just 5 µ m and an improved signal-to-noise ratio. With a basic understanding of the technical differences be-tween conventional and SS-OCT we can now explore the advan-tages of this new technology. Advantages of SS-OCT A major advantage of SS-OCT is the high imaging speed, which allows high-resolution images to be obtained while reducing the negative effect of patient’s eye movements on scan quality. SS-OCT also uses an invisible light source, which is less distracting for patients compared to the visible light used in SD-OCT. The long wavelength and swept-source technology also provide the ability to obtain clear images of deep ocular structures such as the choroid and lamina cribrosa, the putative site of axonal damage in glau-coma. 1,2 Imaging of deep struc-Sponsored by tures is possible, as the long wavelength of SS-OCT is less subject to light scatter by the retinal pigment epithelial (RPE). There is also less light scattering by lens opacities and therefore, SS-OCT can provide clearer im-ages in patients with cataracts compared to conventional OCT. A further advantage of swept-source technology is that it provides uniform sensitivity over the entire scan window, which enables the vitreous, retina and deep ocular structures to be visu-alized in a single scan. In compar-ison, conventional SD-OCT does not have the same capability and suffers from a drop off in sensitiv-ity with changing scan depth. Topcon’s Deep Range Imaging OCT-1 (Atlantis)* is an example of an SS-OCT device for poste-rior ocular imaging. An attrac-tive feature of this SS-OCT is its ability to perform a wide-fi eld scan covering a 12-x 9-mm area of the posterior pole. Using the wide-fi eld protocol, the disc and macula can be evaluated in a sin-gle scan. This has the potential to improve our understanding of the relationship between the optic nerve and macular damage and overcomes the problems caused by differences in head position and alignment when

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