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OCT spurs new developments in all aspects of eye care
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The world of ophthalmology has changed irrevocably since the advent of optical coherence tomography, a non-contact, noninvasive imaging technique that provides high-resolution tomographic images of ocular microstructures.
The old version of OCT, time-domain OCT (TD-OCT), revolutionized ocular imaging when it first appeared years ago by elucidating subtle details of ocular tissue morphology imperceptible by any former technologies, but its clinical application was constrained by relatively low speed, limited resolution and suboptimal quality. An advance in technologies led to the second-generation OCT, spectral-domain OCT (SD-OCT, also known as Fourier-domain or high-definition OCT), which can provide up to 65 times higher resolution and scan 100 times faster than TD-OCT. SD-OCT scans so fast that it can minimize and even efface the impact of patients’ involuntary movement related to heartbeat and breathing.
The groundbreaking structural details and subtleties offered by SD-OCT have made it a compelling choice for imaging ocular pathologies, in particular retinal diseases and glaucoma. Robust image acquisition and digital modification have conferred further versatilities to ocular imaging by making possible 3-D image manipulation, reconstruction of corneal mapping, optic disc nerve fiber layer mapping and macular mapping. SD-OCT has probably redefined the standard of ophthalmic practice from general ophthalmologists to subspecialists. Its impact on patients is equally staggering because patients can, for the first time, visually perceive the images of the diseases, with better comprehension and understanding.
The ubiquitous infiltration of SD-OCT technology into daily ophthalmic practices is not without problems because it can create uncertainties. For users, the uncertainty is about which OCT to choose, given that there are more than 10 ophthalmic OCT system vendors available. Although most of the SD-OCT platforms have similar performance in terms of speed and resolution, the measurements generated by different platforms are not directly comparable. Therefore, one should avoid using one OCT platform for baseline measurement on one occasion while using another platform for tracking progression in the same individual later on. For health care systems, determining the clinical appropriateness of an OCT scan is of paramount importance. For instance, of the tens of millions of OCTs being performed globally each year, how many of them are actually clinically indicated or justified? This issue has an important financial bearing on the frail health care system because health care costs can soar at an almost unsustainable pace worldwide. This uncertainty highlights the need to develop clear-cut clinical rules and criteria based on a combination of evidence and expert opinion.
OCT technology has no equal alternative, but there is still room for improvement. Notably, the resolution of current anterior segment OCT is still suboptimal. Another promising technological conglomerate is the integration of real-time OCT (either handheld or mounted) with surgical microscopes for therapeutic procedures such as corneal refractive surgery, corneal transplantation surgery, macular surgery and femtosecond laser-assisted cataract surgery. In addition, future technological developments of polarization-sensitive OCT will allow us to evaluate the health and biological status of retinal pigment epithelial cells. New technologies such as long-wavelength SD-OCT and enhanced-depth imaging may allow a better morphological assessment of the deeper structures below the retinal pigment epithelium, whereas the sophisticated hybrid photoacoustic and Doppler OCT may be used to accurately detect retinal and choroidal blood flow.
References:
Brenner DJ. N Engl J Med. 2010;doi:10.1056/NEJMe1000802.
Gabriele ML, et al. Prog Retin Eye Res. 2010;doi:10.1016/j.preteyeres.2010.05.005.
Huang D, et al. Science. 1991;doi:10.1126/science.1957169 254(5035):1178-1181.
For more information:
Dennis S.C. Lam, MD, FRCOphth, can be reached at State Key Laboratory in Ophthalmology, Sun Yat-Yen University, 54 South Xianlie Road, Guangzhou 510060, People’s Republic of China; +852-3997-3266; fax: +852-3996-8212; email: dennislam.gm@gmail.com.