Diagnostics
SD-OCT Technology Races Forward
Get up to speed on the latest advances in spectral domain OCT systems
One of the fascinating developments in recent years is the technological leap made by ocular coherence tomography (OCT) systems. This non-contact transpupillary imaging technology originally provided imaging of retinal structures. Today's spectral domain OCT (SD-OCT) systems not only provide higher resolution of the posterior segment at much faster speeds than previous time domain (TD-OCT) systems, they also offer a number of features including three-dimensional mapping, cross-sectional imaging and anterior segment imaging. One of the most interesting new applications of the technology is intraoperative OCT, which was recently described by our sister publication, Retinal Physician: http://www.retinalphysician.com/articleviewer.aspx?articleid=106159.
While it would take an expansive article to present all the latest features of each manufacturer's SD-OCT system, we offer a sampling below. (For complete technical information and updated specifications, we recommend you contact the manufacturer.)
Bioptigen (www.bioptigen.com)
While intended primarily for imaging retinal tissue, with a switch of focus this company's SD-OCT system can be used to capture images of the cornea, sclera, and conjunctiva, according to Bioptigen's website.
The system may interest both researchers and clinicians as it allows either to resolve the retina's microstructure in fine detail. The structural details that can be elucidated include the retinal nerve fiber layer, the inner and outer plexiform and nuclear layers, the retinal pigment epithelium, and choroidal vessels.
Carl Zeiss Meditec (www.carlzeissmeditec.com)
Zeiss's new Cirrus OCT software version 6.0 provides cross-sectional images and maps showing details of retinal changes otherwise difficult to spot. In addition, quantitative analysis of retinal features facilitates not only the initial diagnosis, but also ongoing monitoring or treatment. Scans produce opportunities to analyze the retinal nerve fiber layer, optic nerve head, and macular thickness at the present moment and serially from there.
Specifically, the new software features advanced RPE analysis (model 4000 only) ganglion cell analysis, Enhanced GPA (Guided Progression Analysis) with ONH (optic nerve head) Change Analysis.
Heidelberg Engineering (http://www.heidelbergenginee ring.com/us/)
Heidelberg received FDA clearance in March, 2011, for its Spectralis OCT anterior segment module. The upgrade reportedly provides high-resolution images of the cornea, anterior chamber angle, and sclera. Clinicians can assess both angles at once using a 16 mm-wide angle-to-angle OCT scan.
Heidelberg's Spectralis integrates spectral-domain OCT with confocal scanning laser ophthalmoscopy. The two technologies enable new imaging capabilities, such as an eye-tracking function as well as blue laser autofluorescence.
Optos (www.optos.com)
The Optos Spectral OCT/SLO imaging system includes several additional features, primarily a confocal scanning laser ophthalmoscope for enhanced diagnostics of retinal diseases and glaucoma. Its imaging quality can capture macular and sub-retinal layer definition as well as vitreous and vitreo-retinal layers. It also features 3D topography with an autocompare feature, which is designed to allow comparison of retinal thickness in multiple topographic maps taken over an extended period.
In addition, the Optos system helps the technician communicate with patients with it's viewer software, which is accessible from a remote computer and displays scans, and optic nerve analysis.
Optovue (www.optovue.com)
Optovue's OCT systems now offer the flexibility of paying on a per-use basis, which can minimize up-front cost. Its new RTVue XR system features a 70,000 A-scan per second camera, reportedly nearly three times faster than some other systems. The RTVue's eye-tracking software yields precise image detail with a retinal scanning depth of nearly 3 mm.
The RTVue's capacity to measure corneal powers for IOL calculations is also worth mentioning. Perhaps the greatest benefit in this case is for post-refractive patients with altered corneal curvatures. The RTVue measures both the cornea's front and back surfaces. The company's iVue OCT system, meanwhile, offers a lower-priced, portable alternative often used for screening purposes.
Topcon Medical Systems (www.topconmedical.com)
Topcon's 3D OCT-2000 system— with its reportedly user-friendly and easily navigable color touch screen display and compact foot-print—incorporates a high-resolution fundus camera. Topcon's software allows dynamic viewing of two- and three-dimensional fundus images at once.
Three-dimensional imaging may enhance a clinician's understanding of complex pathologies such as vitreous traction, macular edema, and retinoschisis, according to Topcon's website. The built-in fundus camera, meanwhile, allows you to inspect conditions that might be missed on OCT such as disc hemorrhages. Topcon's software is said to use 3D registration technology to reduce artifacts caused by eye movement.
The company's thickness-measurement function includes both overall retinal thickness and the retinal nerve fiber layer. A mosaic-type image display reportedly creates panoramic views from the macula to the optic disc. OP
Portions of this article were adapted from “A Winning Combination, “ which appeared in the July issue of Ophthalmology Management.
| The Future of OCT Systems |
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| Just as today's OCT systems feature significant advances over units from the previous generation, newer generations of OCT systems will provide clearer image resolution and advanced capabilities to better meet the demands of the practice. Here's a glimpse into the future:• Swept-source OCT. SS-OCT technology uses a narrowband light source with a cavity-swept laser that can emit different light frequencies and that turns rapidly over a broad bandwidth. The system achieves rates of 100,000-400,000 A-scans per second with 5-mm tissue axial resolution over a 4-mm imaging range.The SS-OCT allows for fewer patient-induced artifacts from movement and breathing, plus better penetration through cataracts or other opacities. • Adaptive optics. Adaptive optics correct images for higher-order ocular aberrations and allow for near-cellular image resolution. Ultra-high-resolution adaptive optics uses a high-speed CMOS camera with a novel image-registration/de-warping algorithm to limit motion artifacts, increase lateral resolution, reduce speckle and enhance sensitivity.• Full-field OCT. Based on spatial coherence grating, this technology uses narrow-band illumination with high-numerical aperture objectives and a liquid crystal retarder to minimize defocusing and dispersion effects. This allows for three-dimensional imaging with ultra-high resolution.• Intraoperative OCT. Intraoperative SD-OCT helps surgeons better delineate tissue structures, reducing surgical time, excessive illumination and the need for potentially toxic stains.• Wide-field OCT. Wide-field OCT applies swept-source technology to evaluate larger swaths of the central retina. Image acquisition occurs at speeds of 684,000-1,368,700 A-scans per second. Multiple data sets are consolidated into a four-megapixel, high-definition image.• Doppler OCT. This technology allows the operator to assess blood-flow velocity. Blood-flow measurements can be evaluated from the transection of all branch retinal arteries and veins using eight circular scans, each composed of 3,000 axial scans, with the total captured in about two seconds.• Functional OCT. Also known as polarization-sensitive (PS) OCT, this method assesses functional tissue by evaluating light polarization. It allows the operator to identify individual retinal layers by measuring cross-sectional and volumetric birefringence. |
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