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Diabetic Retinopathy Highlights from LEO Clinical Update Course on Retina
Advances in Diagnostic Imaging
| Sunday, November 12, 2006 |
| Jason S Slakter, MD
FA remains the primary imaging modality used in the diagnosis and treatment of DR and CRVO/BRVO. OCT use is expanding as it can detect cystic changes of the macula earlier than FA or clinical examination. OCT also provides quantitative macular thickness data. Ultrasonography may be used in place of FA and OCT when vitreous hemorrhage obscures the retina. Clinical exam, FA, OCT, and ultrasound cannot be substituted for each other. Each type of instrument provides information that is not available from the others. The technologies may be used in a mutually complementary fashion.
OCT permits noninvasive, noncontact imaging and its clinical use has increased exponentially since its introduction. Axial resolution of typical devices is around 10 microns, permitting resolution of intraretinal detail. Several manufacturers introduced so-called spectral domain OCT instruments at this meeting. These devices permit resolution down to an astonishing 3 nanometers, permitting resolution of the internal and external limiting membranes and the junction between inner and outer segments. These devices acquire tens of thousands of axial scans per second. Retinal cross-sectional images are provided in real time, and even 3D reconstructions from these scans can be produced at a speed acceptable for routine clinical use. A limitation of previously available OCT systems was the lack of registration between the retinal scan and its corresponding location on the retina. This limitation has been overcome in the spectral domain OCT instruments now available.
Although not as glamorous as OCT, ultrasound is indispensable for retinal imaging in the presence of media opacity, as may occur in vitreous hemorrhage or retinal detachment. Ultrasound imaging has improved in resolution and image quality. Some instruments permit “stacking� of multiple 2D B-scans to make a reconstructed 3D image. The scanning procedure permitting 3D images is clinically practical at about 4 seconds. Ultrasound “movies� can also be generated, a useful viewing mode for qualitative determination of the dynamic tension in the membranes of a tractional retinal detachment. Ultrasound movies also have potential applications in resident training and patient education. |
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