The Experts below are selected from a list of 147 Experts worldwide ranked by ideXlab platform
Carmem S Pfeifer - One of the best experts on this subject based on the ideXlab platform.
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polymerization development of low shrink resin composites reaction kinetics polymerization stress and quality of network
Dental Materials, 2013Co-Authors: L C Yamasaki, Andre Guaraci De Vito Moraes, Mathew Barros, S H Lewis, Carlos Eduardo Francci, Jeffrey W Stansbury, Carmem S PfeiferAbstract:a b s t r a c t Objectives. To evaluate “low-shrink” composites in terms of polymerization kinetics, stress development and mechanical properties. Methods. “Low-shrink” materials (Kalore/KAL, N’Durance/NDUR, and Filtek P90/P90) and one control (Esthet X HD/EHD) were tested. Polymerization stress (PS) was measured using the Instron 5565 tensometer. Volumetric shrinkage (VS) was determined by the ACTA linometer. Elastic modulus (E) and flexural strength (FS) were obtained by a three-point bending test. Degree of conversion (DC) and polymerization rate (Rp) were determined by NIR spectroscopy (6165 cm −1 for dimethacrylates; 4156 and 4071 cm −1 for P90). Photopolymerization was per
Granger Sunderland - One of the best experts on this subject based on the ideXlab platform.
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evaluation of an opacity Lensometer for determining corneal clarity following excimer laser photoablation
Journal of Refractive Surgery, 1990Co-Authors: Helia Angotti Andrade, Mohamed Abdelmegeed, Ray J Varnell, Marguerite B. Mcdonald, Granger SunderlandAbstract:The appearance of haze in the central cornea following photoablation with a 193 nm excimer laser is an important factor in the postoperative course of this procedure. Data from 37 human eyes treated with photorefractive keratectomy, 4 eyes treated with phototherapeutic keratectomy, and 5 untreated eyes were used to evaluate the ability of a commercially available opacity Lensometer to provide an objective measure of corneal clarity. We found that the opacity Lensometer was able to detect light scattered from the cornea but was not sufficiently sensitive to distinguish reliably among excimer-treated eyes with degrees of corneal haze evaluated as clear, trace, or 1+ by slit-lamp microscope examination. In untreated, clear corneas, the values obtained with the opacity Lensometer in eyes measured with and without a clear contact lens were within one unit of each other for any given eye, but values from eye to eye varied over a range of six units. In a test simulating different amounts of corneal haze using contact lenses evenly coated with nail polish enamel, the log-transformed opacity Lensometer values varied directly with percent light scattering as determined by spectrophotometry. These results suggest that the opacity Lensometer measurements are reliable and reproducible, but that inmore » the human cornea something is being measured by the opacity Lensometer that is not taken into account in clinical slit-lamp microscope evaluation. Overall, it appears that, in its present form, this instrument is not useful to measure corneal clarity after excimer laser photoablation.« less
Helia Angotti Andrade - One of the best experts on this subject based on the ideXlab platform.
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evaluation of an opacity Lensometer for determining corneal clarity following excimer laser photoablation
Journal of Refractive Surgery, 1990Co-Authors: Helia Angotti Andrade, Mohamed Abdelmegeed, Ray J Varnell, Marguerite B. Mcdonald, Granger SunderlandAbstract:The appearance of haze in the central cornea following photoablation with a 193 nm excimer laser is an important factor in the postoperative course of this procedure. Data from 37 human eyes treated with photorefractive keratectomy, 4 eyes treated with phototherapeutic keratectomy, and 5 untreated eyes were used to evaluate the ability of a commercially available opacity Lensometer to provide an objective measure of corneal clarity. We found that the opacity Lensometer was able to detect light scattered from the cornea but was not sufficiently sensitive to distinguish reliably among excimer-treated eyes with degrees of corneal haze evaluated as clear, trace, or 1+ by slit-lamp microscope examination. In untreated, clear corneas, the values obtained with the opacity Lensometer in eyes measured with and without a clear contact lens were within one unit of each other for any given eye, but values from eye to eye varied over a range of six units. In a test simulating different amounts of corneal haze using contact lenses evenly coated with nail polish enamel, the log-transformed opacity Lensometer values varied directly with percent light scattering as determined by spectrophotometry. These results suggest that the opacity Lensometer measurements are reliable and reproducible, but that inmore » the human cornea something is being measured by the opacity Lensometer that is not taken into account in clinical slit-lamp microscope evaluation. Overall, it appears that, in its present form, this instrument is not useful to measure corneal clarity after excimer laser photoablation.« less
Charles R Munnerlyn - One of the best experts on this subject based on the ideXlab platform.
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Analysis of an adjustable slit design for correcting astigmatism
Ophthalmic Technologies, 1991Co-Authors: Terrance N Clapham, Peter J Mcdonnell, Charles R Munnerlyn, John D'arcy, Lorne Bechtel, Hermann J. Glockler, Jenny J GarbusAbstract:Using 193 nrn Excimer Laser light to reshape the cornea has been shown to be an effective way to correct myopia in man"2 One way to achieve the controlled shape is to create a large diameter Excimer beam, and pass it through a computer controlled ins diaphragm. As the diaphragm closes, progressively less laser pulses reach the outer portions of the treatment area, while all the pulses reach the center region, effectively flattening the cornea. The resultant correction is spherical, and does not correct astigmatism. This paper discusses the use of a motor controlled slit to correct astigmatism in a similar manner to myopia. The mechanism described combines an iris diaphragm and adjustable slit for correcting myopia, astigmatism, or a combination of the two. The slit mechanism also rotates so the slit axis can be aligned with the patient's astigmatic axis. All motions are motor driven under computer control, with encoder feedback to ensure correct positioning. Initial test medium was PMMA, which has ablation characteristics similar to human stromal tissue. Mechanical profile scans and Lensometer tests of the PMMA test blocks were performed to verify the correct ablation pattern. Animal eyes were ablated and tested for astigmatic induction.
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photorefractive keratectomy to create toric ablations for correction of astigmatism
Archives of Ophthalmology, 1991Co-Authors: Peter J Mcdonnell, Hamilton Moreira, Jenny J Garbus, Terrance N Clapham, John Darcy, Charles R MunnerlynAbstract:• Excimer laser photorefractive keratectomy, developed to perform radially symmetric ablations to correct myopic or hyperopic refractive errors, was used to create toric ablations designed to correct cylindrical errors. An expanding slit was created, with no refractive change intended parallel to the slit opening, and central flattening was induced in the meridian in which the slit was expanded. In polymethyl methacrylate blocks, the induced cylinder (as measured with a Lensometer) agreed closely ( r 2 =.99) with the intended change, and in plastic corneas, induction of the cylinder could be demonstrated with computer-assisted topographic analysis. Adult pigmented rabbits underwent induction of toric ablations in two-diopter increments; measured keratometric change correlated with desired change ( r 2 =.87 at 3 weeks; r 2 =.89 at 12 weeks). Toric ablations with the excimer laser appear to represent a promising strategy for the correction of cylindrical errors that do not rely on creation of deep corneal incisions, excisions, or compression sutures.
Jean-marie Parel - One of the best experts on this subject based on the ideXlab platform.
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Optical power of the isolated human crystalline lens.
Investigative ophthalmology & visual science, 2008Co-Authors: David Borja, Arthur Ho, Noel Ziebarth, Alexandre M Rosen, Rakhi Jain, Adriana Amelinckx, Robert C. Augusteyn, Fabrice Manns, Esdras Arrieta, Jean-marie ParelAbstract:PURPOSE: To characterize the age dependence of isolated human crystalline lens power and quantify the contributions of the lens surfaces and refractive index gradient.\n\nMETHODS: Experiments were performed on 100 eyes of 73 donors (average 2.8 +/- 1.6 days postmortem) with an age range of 6 to 94 years. Lens power was measured with a modified commercial lensmeter or with an optical system based on the Scheiner principle. The radius of curvature and asphericity of the isolated lens surfaces were measured by shadow photography. For each lens, the contributions of the surfaces and the refractive index gradient to the measured lens power were calculated by using optical ray-tracing software. The age dependency of these refractive powers was assessed.\n\nRESULTS: The total refractive power and surface refractive power both showed a biphasic age dependency. The total power decreased at a rate of -0.41 D/y between ages 6 and 58.1, and increased at a rate of 0.33D/y between ages 58.1 and 82. The surface contribution decreased at a rate of -0.13 D/y between ages 6 and 55.2 and increased at a rate of 0.04 D/y between ages 55.2 and 94. The relative contribution of the surfaces increased by 0.17% per year. The equivalent refractive index also showed a biphasic age dependency with a decrease at a rate of -3.9 x 10(-4) per year from ages 6 to 60.4 followed by a plateau.\n\nCONCLUSIONS: The lens power decreases with age, due mainly to a decrease in the contribution of the gradient. The use of a constant equivalent refractive index value to calculate lens power with the lens maker formula will underestimate the power of young lenses and overestimate the power of older lenses.