Optometric Office

MAR 2016

Products and their applications for optometry.

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Ever since optical coherence tomography (OCT) was first introduced in 1991, it has offered a standardized, objective method of quantifying subtle nerve tissue loss in a quick and non-invasive way. Although the gold standard of glaucoma manage- ment is still optic nerve head (ONH) as- sessment and visual field perimetry, the OCT provides a more sensitive approach to glaucoma management for earlier diag- nosis and treatment. The top four companies that produce OCTs are Carl Zeiss Meditec, Inc. (Cirrus HD-OCT), OptoVue, Inc. (Avanti Widefield OCT), Topcon Medi- cal Systems, Inc. (3D OCT-2000) and Heidelberg Engineering, Inc. (Spectralis SD-OCT). Each company has its own pro- prietary analysis software, scan methods and display formats, but most standard OCTs contain a basic assessment of the circumpapillary retinal nerve fiber layer (RNFL) thickness. However, new advances in OCT soft- ware can now perform macular thickness scans to assess ganglion cell complexes, obtain large-area scans that incorporate both optic nerve and macula in a single display and include progression analysis software to compare baseline and follow- up scans.) BEYOND THE GOLD STANDARD Though ONH assessment and visual field perimetry are the foundations in manage- ment and detection of glaucoma, the OCT is a valuable adjunct. OCT offers an objec- tive and quantitative measurement that largely bypasses patient error. The shift from time domain to spectral domain OCT has enhanced resolution two- to three-fold and increased scan speed 60- to 100-fold, allowing a great deal of information to be obtained in a short amount of time. Given the ease of use, valuable quantitative measurements and short scan duration, OCT can be regularly performed to establish a baseline for glau- coma suspects and to assess for change in glaucoma management. However, the OCT is not a perfect sys- tem; there are a number of limitations when interpreting the data. Patient data is compared to a normative database that is unique to each company. If a patient falls outside of the norm, such as with a refrac- tive error beyond the +12.00D to -8.00D range, the RNFL can give false negative and false positive results; similarly so with anomalous optic nerves. Also, inter-machine comparisons of the RNFL measurements are inconsistent, so retinal and optic nerve measurements should only be compared within each in- strument. OCT artifacts need to be viewed carefully and can come from a variety of By Amiee Ho, OD, and Hannah Shinoda, OD Advances in OCT technology will help diagnose and better manage patients with glaucoma. Pushing the Boundaries of Early Glaucoma Detection INSTRUMENTATION The 3mm scan depth and 40° scanning of the Avanti Widefield OCT from Optovue provide the detail and clarity to assess the retina. * 10 M a r c h 2 0 1 6 | o p t o m e t r i c o f f i c e . c o m The 3D OCT-2000 from Topcon features intuitive FastMap software that can provide 3D, 2D and fundus images simultaneously.

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