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Selected AbstractsDetermination of pseudophakic accommodation with translation lenses using Purkinje image analysisOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 2 2005Achim Langenbucher Abstract Purpose:, To determine pseudophakic accommodation of an accommodating posterior chamber intraocular lens (translation lens) using Purkinje image analysis and linear matrix methods in the paraxial space. Methods:, A 2 × 2 system matrix was defined for each Purkinje image I to IV using refraction, translation and mirror matrices. Image size (m) and axial image position (z) was determined as an example for an off-axis object (a 0.2 m off-axis object located 0.5 m in front of the cornea.). First, our method was applied to the phakic relaxed (emmetropic) and accommodated (6.96 D) Le Grand eye. Secondly, for demonstration of the applicability of the calculation scheme to the pseudophakic eye, we provide a clinical example where we determine the accommodation amplitude of the translation lens (1 CU, HumanOptics, Erlangen, Germany) from photographed Purkinje images in the relaxed and accommodated state. From the biometric data: axial length 23.7 mm, corneal power 43.5, corneal thickness 550 microns, implanted intraocular lens (IOL) with a refractive power of 20.5 D (shape equi-biconvex, refractive index 1.46), and refractive indices of the cornea, aqueous and vitreous from the Le Grand model eye, we calculated the refractive state and the sizes of Purkinje images I and III initiated from two off-axis light sources. Results:, For the Le Grand model eye, Purkinje image II (z/m = 3.5850 mm/0.0064) is slightly smaller than and directly in front of image I (z/m = 3.8698 mm/0.0077). Purkinje image III (z/m = 10.6097 mm/0.0151) is nearly double the size of image I and during accommodation it moves from the vitreous into the crystalline lens. Purkinje IV (z/m = 4.3244 mm/,0.0059) is inverted, three quarters the size of image I, lies in the crystalline lens and moves slightly towards the retina. For the pseudophakic eye, pseudophakic accommodation of 1.10 D was calculated from the proportion of distances between both Purkinje images I and III in the relaxed (3.04) and accommodated (2.75) state, which is in contrast to the total subjective accommodation of 2.875 D evaluated with an accommodometer. Conclusions:, We present a straightforward mathematical strategy for calculation of the Purkinje images I,IV. Results of our model calculation resemble the values provided by Le Grand. In addition, this approach yields a simple en bloc scheme for determination of pseudophakic accommodation in pseudophakic eyes with accommodative lenses (translation lenses) using Purkinje image photography. [source] Optimal Representative Blocks for the Efficient Tracking of a Moving ObjectJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 3 2004SangJoo Kim Optimal representative blocks are proposed for an efficient tracking of a moving object and it is verified experimentally by using a mobile robot with a pan-tilt camera. The key idea comes from the fact that when the image size of a moving object is shrunk in an image frame according to the distance between the camera of mobile robot and the moving object, the tracking performance of a moving object can be improved by shrinking the size of representative blocks according to the object image size. Motion estimation using edge detection (ED) and block-matching algorithm (BMA) are often used in the case of moving object tracking by vision sensors. However, these methods often miss the real-time vision data since these schemes suffer from the heavy computational load. To overcome this problem and to improve the tracking performance, the optimal representative block that can reduce a lot of data to be computed is defined and optimized by changing the size of the representative block according to the size of object in the image frame. The proposed algorithm is verified experimentally by using a mobile robot with a two degree-of-freedom active camera. © 2004 Wiley Periodicals, Inc. [source] X-ray diffraction topography using a diffractometer with a bendable monochromator at a synchrotron radiation sourceJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2002D. Altin The different properties of laboratory- and synchrotron-based double-crystal setups for X-ray topographic applications are discussed as a basis for the realization of a versatile instrument allowing the investigation of all kinds of crystals with high strain sensitivity and without any reduction in image size. It appears that the use of a bendable highly perfect monochromator (silicon) achieves this goal, through the local adaptation of Bragg angles, to compensate either dispersion or a bending of the sample. [source] Compensation of aniseikonia in astigmatic pseudophakic eyes,OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 6 2005Graeme E. MacKenzie Abstract Purpose:, A recently published manuscript addressed the problem of compensating for aniseikonia between pseudophakic astigmatic eyes using a least-squares calculation scheme. The purpose of this paper is to revisit this topic with the specific aim of providing explicit formulae for the determination of the intra-ocular lens required to produce a specified transverse image size at the plane of the retina and the characteristics of the contact or spectacle lens required to realize some desired refractive outcome. Methods:, The 4 × 4 ray transference is central to the development of all formulae presented in this paper. Specifically, the formula for the determination of the power of the intra-ocular lens required to achieve some transverse image size at the retina is derived directly from the disjugacy of the pseudophakic eye. Results:, The formula is applicable to both stigmatic and astigmatic systems without restriction. A detailed numerical example for an unusual eye is provided. Conclusion:, A formula for the determination of the intra-ocular lens required to produce any given transverse image size at the retina is derived. This approach does not require the application of the Moore-Penrose pseudo-inverse and one is able to work rather with the properties of the optical system directly without further modification. [source] Computerized calculation scheme for retinal image size after implantation of toric intraocular lensesACTA OPHTHALMOLOGICA, Issue 1 2007Achim Langenbucher Abstract. Purpose., To describe a paraxial computing scheme for tracing an axial pencil of rays through the ,optical system eye' containing astigmatic surfaces with their axes at random. Methods., Two rays (,10 prism diopters from vertical and horizontal) are traced through the uncorrected and corrected eye. In the uncorrected eye one specific ray is selected from the pencil of rays, which passes through the pupil center. In the corrected eye any ray can be traced through the eye. From the slope angle, the intersection of the ray with the refractive surface and the refraction the slope angle of the exiting ray is determined and the ray is traced to the subsequent surface. From both rays traced through the eye an ellipse is fitted to the image to characterize the image distortion of an circular object. Example., Assumptions: target refraction ,0.5,1.0D/A = 90° at 14 mm, corneal refraction 42.5 + 3.5D/A = 15°, axial length 23.6 mm, IOL position 4.6 mm, central lens thickness 0.8 mm, refractive index 1.42, front/back surface of the toric IOL 10.0 D/7.14 + 6.47D/A = 101.8°. The vertical incident ray was imaged to (x, y) = (0.0055 mm, ,1.6470 mm)/(0.0067 mm, ,1.6531 mm) in the uncorrected/corrected eye. The horizontal incident ray was imaged to (x, y) = (1.6266 mm, ,0.0055 mm)/(1.6001 mm, ,0.0067 mm) in the uncorrected/corrected eye. The ellipse (semi-major/semi-minor meridian) fitted to the conjugate image of a circle sized 1.648 mm/1.625 mm in an orientation 14.2° in the uncorrected and 1.654 mm/1.599 mm in an orientation 7.1° in the corrected eye. Conclusion., This concept may be relevant for the assessment of aniseikonia after implantation of toric intraocular lenses for correction of high corneal astigmatism. [source] Real-Time Temporal-Coherent Color Contrast Enhancement for DichromatsCOMPUTER GRAPHICS FORUM, Issue 3 2010Gustavo M. Machado Abstract We present an automatic image-recoloring technique for enhancing color contrast for dichromats whose computational cost varies linearly with the number of input pixels. Our approach can be efficiently implemented on GPUs, and we show that for typical image sizes it is up to two orders of magnitude faster than the current state-of-the-art technique. Unlike previous approaches, ours preserve temporal coherence and, therefore, is suitable for video recoloring. We demonstrate the effectiveness of our technique by integrating it into a visualization system and showing, for the first time, real-time high-quality recolored visualizations for dichromats. [source] Comparison of 1- and 2-Marker Techniques for Calculating System Magnification Factor for Angiographic Measurement of Intracranial VesselsJOURNAL OF NEUROIMAGING, Issue 4 2005A. A. Divani PhD ABSTRACT Background and Purpose. Accurate estimation of an intracranial vessel size is crucial during a diagnostic or therapeutic angiography procedure. The use of 1 or 2 external markers of known size is previously proposed to manually estimate the magnification factor (MF) of an intracranial vessel. The authors evaluated the use of different external marker techniques commonly used during angiographic measurements. Methods. Forty-three intracranial vessels in 17 patients were measured using 1-and 2-marker techniques. To obtain the MF, 2 metallic markers were attached to the frontal-temporal regions. The MFs for the targeted vessels were obtained from the x-ray films by measuring the image sizes of the markers and their positions with respect to the target vessel. Results. Using a phantom, the errors resulted from (a) linear interpolation of MFs, (b) linear interpolation of inverse MFs, and (c) using the MFs of 1 marker, which were 1.23% to 2.23%, 0.8% to 1.55%, and 3.85% to 14.62%, respectively. A similar trend was observed for the measurement of cerebral arteries. Conclusion. The use of 2 markers can result in a more accurate estimation of the vessel size. The use of only 1 external marker can lead to substantial error based on the location of the target vessel. Optimizing image acquisition is also crucial for accurate determination of vessel size. [source] | ||||||||||