CLINICAL COMPARISON OF RETINAL THICKNESS ANALYSER (RTA) AND OPTICAL COHERENCE TOMOGRAPHY (OCT). FIRST RESULTS BASED ON TYPICAL RETINAL DISEASES.C. Niederdellmann, M.J. Thiel, J.V. Münich, A. Scheider, M.W. Ulbig
Currently, two noninvasive tools (OCT and RTA) are available for diagnostic imaging of the retina which analyse light which is backscattered from retinal layers. In this study we compared clinical usability and ease of use of both systems.
Methods: RTA: A laser beam (540 HeNe laser) with a power of 180m W scans an area of 2 x 2 mm within 200 msec. Light which is reflected from the inner limiting membrane and the retinal pigment epithelium (RPE) is collected with a CCD camera and digitised. A computer calculates a 2- and a 3-dimensional image with a practical resolution of 30 m m. For imaging of the posterior pole 9 squares (each 2 x 2 mm) are measured.
OCT: Light which is emitted from a superluminescent diode is split into a reference beam and a probe beam. The backscatter of both beams is collected and interference calculated by a computer. Digital image processing software creates a 2-dimensional scan of the retina with a resolution of 10 m m.
Patients: We examined 26 eyes with RTA and OCT. Diagnoses included diabetic retinopathy (6), macular edema resulting from vasculitis (2), macular edema resulting from venous occlusion (3), central serous retinopathy (4), choroidal neovascularisation (1), multifocal chorioretinitis (2) and vitreoretinal traction (8).
Results: Both systems yielded comparable results in the analysis of epiretinal and retinal structures. OCT was advantageous in that it could detect small epiretinal membranes and macular holes due to its better resolution. OCT and RTA were equally able to diagnose intraretinal diseases e.g. bleeding and macular edema. The RTA allows better visual illustration as it computes a chart of the posterior pole. The ability of the OCTs infrared light to partially penetrate the RPE permits to evaluate structures in the subretinal compartrnent. In some cases measurements did not produce identical results. Both systems depend on reasonable clear optical media.
Conclusion: The comparison demonstrates advantages and disadvantages of both systems. The cases reported in this study show the different usability in clinical practice.
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