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| Scanning Laser Doppler Flowmetry System for Two-Dimensional Mapping of the Ocular Perfusion The Heidelberg Retina Flowmeter uniquely merges two sophisticated measurement techniques, confocal laser scanning and laser Doppler flowmetry, to a new kind of instrument that provides non-invasive two-dimensional mapping of the retinal micro-circulation. Using an infrared laser, the retina or optic disc is scanned two-dimensionally. Light reflected or scattered at moving objects is frequency shifted due to the optical Doppler effect. It interferes with unchanged light reflected at surrounding tissue. The interference causes characteristic temporal intensity variations of the measurable reflected light intensity. The Heidelberg Retina Flowmeter measures this temporal intensity variation at each point in the two-dimensional scan field by multiple scanning. The Doppler frequency shift of the reflected light is computed from the acquired data and used to quantify the local velocity of moving particles. The excellent performance of this technique allows to resolve blood flow in individual capillaries. The size of the measurement field at the retina is 10° by 2.5° up to 20° by 5°. Within this field, laser Doppler measurements are performed at 256 by 64 independent locations. Total data acquisition time is 2 seconds. No pupil dilation is necessary. Data processing requires only a minute. Two-dimensionally resolved perfusion maps are computed. The perfusion maps provide visualization of the network of perfused capillaries and blood vessels and allow to quantifying the local values of flow, volume, and velocity of the red blood cells. The operation software runs on a standard personal computer. Its functions include database handling, image acquisition, image processing, image contrast enhancement, printout of examination reports with color or black/white printers, and image archiving. Summary of technical data · Field of view (scan size) 10° × 2.5° to 20° × 5° 0.5 to 4.0 mm · Focus range -12 to +12 diopters · Size of perfusion maps 256 × 64 pixels · Optical resolution (limited by the eye) transverse longitudinal 10 µm 300 µm · Digital resolution 10 to 20 µm/pixel Technical specifications are subject to change without notice. Available in combination with the Heidelberg Retina Tomograph.
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| Confocal Laser Scanning System for Quantitative Three-Dimensional Imaging of the Posterior Segment The Heidelberg Retina Tomograph is a confocal laser scanning microscope for acquisition and analysis of three-dimensional images of the posterior segment. It enables the quantitative assessment of the retinal topography and precise follow-up of topographic changes. The most important clinical routine application of Heidelberg Retina Tomograph is the topographic description and follow-up of the glaucomatous optic nerve head. For acquiring digital confocal images, a laser beam is focused to the retina. Oscillating mirrors provide periodic deflection of the laser beam and a two-dimensional field of the retina is scanned sequentially. The reflectance at each point is measured. In the confocal optical setup only light reflected at the adjusted focal plane is measured, whereas out-of-focus light is suppressed. Therefore, a two-dimensional confocal image is an optical section of the retina at the focal plane. Acquisition of a series of optical section images with different locations of the focal plane results in a layer-by-layer three-dimensional image. From the distribution of reflected light in the three-dimensional image, the retinal surface height at each point is computed. The result is a matrix of height measurements that is visualized as the topography image and serves to quantitatively describe the three-dimensional properties of the retinal surface. The Heidelberg Retina Tomograph uses a diode laser with a wavelength of 670 nm. A three-dimensional image is acquired as 32 consecutive and equidistant optical section images, each consisting of 256 × 256 picture elements. The size of the field of view is set to 10° × 10°, 15° × 15°, or 20° × 20°. Pupil dilation is not necessary. Topography images are computed from the acquired three-dimensional images. A topography image consists of 256 × 256 individual height measurements which are absolutely scaled for the individual eye examined and have a reproducibility of the height measurements of approximately 20 microns at each point. The Heidelberg Retina Tomograph operation software provides a variety of functions to quantitatively describe the three-dimensional properties of the retina and the optic nerve head and to precisely detect and describe topographic changes. Interactive measurements provide a simple method to measure distances, height differences and height changes. The stereometric analysis provides a set of stereometric parameters useful for the description of an optic nerve head, for contributing to the diagnosis of glaucoma, and for follow-up of glaucomatous progression. Computation and analysis of topographic difference images and of change probability maps provide additional tools to detect and to quantify topographic changes and progression in glaucoma. The same kind of topographic measurements can also be used to quantify and to follow-up changes of other lesions like macular holes or edema. Summary of technical data · Field of view (scan size) transverse longitudinal 10° × 10° to 20° × 20° 0.5 to 4.0 mm · Focus range -12 to +12 diopters · Digitized image size 2D images 3D images 256 × 256 pixels 256 × 256 × 32 voxels · Scan time per image 2D images 3D images 0.032 seconds 1.6 seconds · Optical resolution (limited by the eye) transverse longitudinal 10 µm 300 µm · Digital resolution transverse longitudinal 10 to 20 µm/pixel 16 to 128 µm/pixel
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Copyright ©2003,Barmed Medical Co. All Rights Reserved. |
