The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
David A. Atchison - One of the best experts on this subject based on the ideXlab platform.
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Change in human Lens dimensions, Lens refractive index distribution and ciliary body ring diameter with accommodation
Biomedical Optics Express, 2018Co-Authors: Adnan Khan, James M. Pope, Pavan Kumar Verkicharla, Marwan Suheimat, David A. AtchisonAbstract:We investigated changes in ciliary body ring diameter, Lens dimensions and Lens refractive index distributions with accommodation in young adults. A 3T clinical magnetic resonance imaging scanner imaged right eyes of 38 18-29 year old participants using a multiple spin echo sequence to determine accommodation-induced changes along Lens axial and equatorial directions. Accommodation stimuli were approximately 1 D and 5 D. With accommodation, ciliary body ring diameter, and equatorial Lens diameter decreased (–0.43 ± 0.31 mm and –0.30 ± 0.23 mm, respectively), and axial Lens thickness increased ( + 0.34 ± 0.16 mm). Lens Shape changes cause redistribution of the Lens internal structure, leading to change in refractive index distribution profiles. With accommodation, in the axial direction refractive index profiles became flatter in the center and steeper near the periphery of the Lens, while in the equatorial direction they became steeper in the center and flatter in the periphery. The results suggest that the anatomical accuracy of Lens optical models can be improved by accounting for changes in the refractive index profile during accommodation.
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Lens Shape and Refractive Index Distribution in Type 1 Diabetes.
Investigative ophthalmology & visual science, 2015Co-Authors: Adnan, James M. Pope, Pavan Kumar Verkicharla, Marwan Suheimat, Farshid Sepehrband, Sanjeev Kasthurirangan, David A. AtchisonAbstract:Purpose - To compare Lens dimensions and refractive index distributions in type 1 diabetes and age-matched control groups. Methods - There were 17 participants with type 1 diabetes, consisting of two subgroups (7 young [23 ± 4 years] and 10 older [54 ± 4 years] participants), with 23 controls (13 young, 24 ± 4 years; 10 older, 55 ± 4 years). For each participant, one eye was tested with relaxed accommodation. A 3T clinical magnetic resonance imaging scanner was used to image the eye, employing a multiple spin echo (MSE) sequence to determine Lens dimensions and refractive index profiles along the equatorial and axial directions. Results - The diabetes group had significantly smaller Lens equatorial diameters and larger Lens axial thicknesses than the control group (diameter mean ± 95% confidence interval [CI]: diabetes group 8.65 ± 0.26 mm, control group 9.42 ± 0.18 mm; axial thickness: diabetes group 4.33 ± 0.30 mm, control group 3.80 ± 0.14 mm). These differences were also significant within each age group. The older group had significantly greater axial thickness than the young group (older group 4.35 ± 0.26 mm, young group 3.70 ± 0.25 mm). Center refractive indices of diabetes and control groups were not significantly different. There were some statistically significant differences between the refractive index fitting parameters of young and older groups, but not between diabetes and control groups of the same age. Conclusions - Smaller Lens diameters occurred in the diabetes groups than in the age-matched control groups. Differences in refractive index distribution between persons with and without diabetes are too small to have important effects on instruments measuring axial thickness.
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MRI study of the changes in crystalline Lens Shape with accommodation and aging in humans.
Journal of vision, 2011Co-Authors: Sanjeev Kasthurirangan, David A. Atchison, Emma L. Markwell, James M. PopeAbstract:Magnetic Resonance Imaging was used to study changes in the crystalline Lens and ciliary body with accommodation and aging. Monocular images were obtained in 15 young (19-29 years) and 15 older (60-70 years) emmetropes when viewing at far (6 m) and at individual near points (14.5 to 20.9 cm) in the younger group. With accommodation, Lens thickness increased (mean ± 95% CI: 0.33 ± 0.06 mm) by a similar magnitude to the decrease in anterior chamber depth (0.31 ± 0.07 mm) and equatorial diameter (0.32 ± 0.04 mm) with a decrease in the radius of curvature of the posterior Lens surface (0.58 ± 0.30 mm). Anterior Lens surface Shape could not be determined due to the overlapping region with the iris. Ciliary ring diameter decreased (0.44 ± 0.17 mm) with no decrease in circumlental space or forward ciliary body movement. With aging, Lens thickness increased (mean ± 95% CI: 0.97 ± 0.24 mm) similar in magnitude to the sum of the decrease in anterior chamber depth (0.45 ± 0.21 mm) and increase in anterior segment depth (0.52 ± 0.23 mm). Equatorial Lens diameter increased (0.28 ± 0.23 mm) with no change in the posterior Lens surface radius of curvature. Ciliary ring diameter decreased (0.57 ± 0.41 mm) with reduced circumlental space (0.43 ± 0.15 mm) and no forward ciliary body movement. Accommodative changes support the Helmholtz theory of accommodation including an increase in posterior Lens surface curvature. Certain aspects of aging changes mimic accommodation.
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Mathematical models for describing the Shape of the in vitro unstretched human crystalline Lens.
Vision research, 2009Co-Authors: George Smith, David A. Atchison, D. Robert Iskander, Catherine E. Jones, James M. PopeAbstract:We developed orthogonal least-squares techniques for fitting crystalline Lens Shapes, and used the bootstrap method to determine uncertainties associated with the estimated vertex radii of curvature and asphericities of five different models. Three existing models were investigated including one that uses two separate conics for the anterior and posterior surfaces, and two whole Lens models based on a modulated hyperbolic cosine function and on a generalized conic function. Two new models were proposed including one that uses two interdependent conics and a polynomial based whole Lens model. The models were used to describe the in vitro Shape for a data set of twenty human Lenses with ages 7–82 years. The two-conic-surface model (7 mm zone diameter) and the interdependent surfaces model had significantly lower merit functions than the other three models for the data set, indicating that most likely they can describe human Lens Shape over a wide age range better than the other models (although with the two-conic-surfaces model being unable to describe the Lens equatorial region). Considerable differences were found between some models regarding estimates of radii of curvature and surface asphericities. The hyperbolic cosine model and the new polynomial based whole Lens model had the best precision in determining the radii of curvature and surface asphericities across the five considered models. Most models found significant increase in anterior, but not posterior, radius of curvature with age. Most models found a wide scatter of asphericities, but with the asphericities usually being positive and not significantly related to age. As the interdependent surfaces model had lower merit function than three whole Lens models, there is further scope to develop an accurate model of the complete Shape of human Lenses of all ages. The results highlight the continued difficulty in selecting an appropriate model for the crystalline Lens Shape.
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Optical design of low index intraocular Lenses
1991Co-Authors: David A. AtchisonAbstract:The effect of Shape of low index (1.43) intraocular Lenses on optical performance of pseudophakic eyes was investigated. A range of image quality criteria was used. The optimum Lens for on-axis vision was biconvex, with the more curved surface facing the cornea. For small off-axis angles, optimum Lens Shape varied with the ocular parameters. A recommended range of intraocular Lenses is plano-convex (with the curved Shape facing the cornea) to equi-convex. Compared with conventional poly(methyl methacrylate) Lenses (1.492 index), optimum Lens Shapes of low index Lenses were less sensitive to changes in eye parameters and Lens fitting position. The magnitudes of aberration of pseudophakic eyes varied more with changes in Lens Shape and Lens position in low index Lenses than in conventional Lenses.
Mark Prince - One of the best experts on this subject based on the ideXlab platform.
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Impact of soft contact Lens edge design and midperipheral Lens Shape on the epithelium and its indentation with Lens mobility.
Investigative ophthalmology & visual science, 2013Co-Authors: James S. Wolffsohn, Tom Drew, Sandeep Dhallu, Amy L. Sheppard, Greg Hofmann, Mark PrinceAbstract:To evaluate the influence of soft contact Lens midperipheral Shape profile and edge design on the apparent epithelial thickness and indentation of the ocular surface with Lens movement. Four soft contact Lens designs comprising of two different plano midperipheral Shape profiles and two edge designs (chiseled and knife edge) of silicone-hydrogel material were examined in 26 subjects aged 24.7 ± 4.6 years, each worn bilaterally in randomized order. Lens movement was imaged enface on insertion, at 2 and 4 hours with a high-speed, high-resolution camera simultaneous to the cross-section of the edge of the contact Lens interaction with the ocular surface captured using optical coherence tomography (OCT) nasally, temporally, and inferiorly. Optical imaging distortions were individually corrected for by imaging the apparent distortion of a glass slide surface by the removed Lens. Apparent epithelial thickness varied with edge position (P < 0.001). When distortion was corrected for, epithelial indentation decreased with time after insertion (P = 0.010), changed after a blink (P < 0.001), and varied with position on the Lens edge (P < 0.001), with the latter being affected by midperipheral Lens Shape profile and edge design. Horizontal and vertical Lens movement did not change with time postinsertion. Vertical motion was affected by midperipheral Lens Shape profile (P < 0.001) and edge design (P < 0.001). Lens movement was associated with physiologic epithelium thickness for Lens midperipheral Shape profile and edge designs. Dynamic OCT coupled with high-resolution video demonstrated that soft contact Lens movement and image-corrected ocular surface indentation were influenced by both Lens edge design and midperipheral Lens Shape profiles.
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impact of soft contact Lens edge design and midperipheral Lens Shape on the epithelium and its indentation with Lens mobility
Investigative Ophthalmology & Visual Science, 2013Co-Authors: James S. Wolffsohn, Tom Drew, Sandeep Dhallu, Amy L. Sheppard, Greg Hofmann, Mark PrinceAbstract:PURPOSE. To evaluate the influence of soft contact Lens midperipheral Shape profile and edge design on the apparent epithelial thickness and indentation of the ocular surface with Lens movement. METHODS. Four soft contact Lens designs comprising of two different plano midperipheral Shape profiles and two edge designs (chiseled and knife edge) of silicone-hydrogel material were examined in 26 subjects aged 24.7 6 4.6 years, each worn bilaterally in randomized order. Lens movement was imaged enface on insertion, at 2 and 4 hours with a high-speed, high-resolution camera simultaneous to the cross-section of the edge of the contact Lens interaction with the ocular surface captured using optical coherence tomography (OCT) nasally, temporally, and inferiorly. Optical imaging distortions were individually corrected for by imaging the apparent distortion of a glass slide surface by the removed Lens. RESULTS. Apparent epithelial thickness varied with edge position (P < 0.001). When distortion was corrected for, epithelial indentation decreased with time after insertion (P ¼ 0.010), changed after a blink (P < 0.001), and varied with position on the Lens edge (P < 0.001), with the latter being affected by midperipheral Lens Shape profile and edge design. Horizontal and vertical Lens movement did not change with time postinsertion. Vertical motion was affected by midperipheral Lens Shape profile (P < 0.001) and edge design (P < 0.001). Lens movement was associated with physiologic epithelium thickness for Lens midperipheral Shape profile and edge designs.
Arezky H. Rodríguez - One of the best experts on this subject based on the ideXlab platform.
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Optical transition in self-assembled InAs/GaAs quantum Lens under high hydrostatic pressure
Journal of Applied Physics, 2009Co-Authors: Arezky H. Rodríguez, C. Trallero-giner, C.a. Duque, Gerardo J. VazquezAbstract:We present a simulation to characterize the dependence on hydrostatic pressure for the photoluminescence spectra in self-assembled quantum dots with Lens Shape geometry. We have tested the physical effects of the band offset and electron-hole effective masses on the optical emission in dot Lens. The model could be implemented to get qualitative information of the parameters involved in the quantum dot or the measured optical properties as function of pressure.
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Contactless electroreflectance of CdSe/ZnSe quantum dots grown by molecular-beam epitaxy
Applied Physics Letters, 2003Co-Authors: Martin Muñoz, S. P. Guo, X. Zhou, Maria C. Tamargo, Ying-sheng Huang, Carlos Trallero-giner, Arezky H. RodríguezAbstract:The interband transitions of a capped CdSe quantum-dot structure have been investigated using contactless electroreflectance. The electroreflectance spectrum shows transitions originating from all the portions of the sample including the quantum dots and the wetting layer. The transitions of the two-dimensional layers have been modeled using an envelope approximation calculation which takes into account the biaxial strain in the wetting layer. A good agreement was found between the experimental values for the transition energies and the calculated ones. From atomic force microscopy measurements, a Lens Shape was observed for the uncapped quantum dots. Taking into account the Lens Shape geometry and assuming that the effective height-to-radius ratio is preserved, the size of the capped quantum dots was determined using the observed electroreflectance transitions, in the framework of the effective mass approximation.
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Stark Effect in Self‐Assembled Quantum Dots with Lens Shape
physica status solidi (b), 2002Co-Authors: Arezky H. Rodríguez, Carlos Trallero-ginerAbstract:The electronic states of a self-assembled quantum Lens (SAQL) under application of a normal electric field are theoretically investigated for different values of the electric field and Lens geometry. Using a conformal analytical image, the Lens boundary and the one particle Hamiltonian are mapped into an equivalent operator defined in a semi-spherical boundary. The complete set of solutions for the Stark effect in a quantum Lens confined by an infinite barrier is reported. The numerical calculations indicate that the interplay of the Lens geometry and the electric field on electrons in the SAQL leads to complicated electron eigenenergies and eigenfunctions. Also, the interactions between states with the same symmetry and anticrossing effects on the energy levels and wavefunctions sharing the same z-angular momentum components are analyzed.
Marwan Suheimat - One of the best experts on this subject based on the ideXlab platform.
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Change in human Lens dimensions, Lens refractive index distribution and ciliary body ring diameter with accommodation
Biomedical Optics Express, 2018Co-Authors: Adnan Khan, James M. Pope, Pavan Kumar Verkicharla, Marwan Suheimat, David A. AtchisonAbstract:We investigated changes in ciliary body ring diameter, Lens dimensions and Lens refractive index distributions with accommodation in young adults. A 3T clinical magnetic resonance imaging scanner imaged right eyes of 38 18-29 year old participants using a multiple spin echo sequence to determine accommodation-induced changes along Lens axial and equatorial directions. Accommodation stimuli were approximately 1 D and 5 D. With accommodation, ciliary body ring diameter, and equatorial Lens diameter decreased (–0.43 ± 0.31 mm and –0.30 ± 0.23 mm, respectively), and axial Lens thickness increased ( + 0.34 ± 0.16 mm). Lens Shape changes cause redistribution of the Lens internal structure, leading to change in refractive index distribution profiles. With accommodation, in the axial direction refractive index profiles became flatter in the center and steeper near the periphery of the Lens, while in the equatorial direction they became steeper in the center and flatter in the periphery. The results suggest that the anatomical accuracy of Lens optical models can be improved by accounting for changes in the refractive index profile during accommodation.
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Lens Shape and Refractive Index Distribution in Type 1 Diabetes.
Investigative ophthalmology & visual science, 2015Co-Authors: Adnan, James M. Pope, Pavan Kumar Verkicharla, Marwan Suheimat, Farshid Sepehrband, Sanjeev Kasthurirangan, David A. AtchisonAbstract:Purpose - To compare Lens dimensions and refractive index distributions in type 1 diabetes and age-matched control groups. Methods - There were 17 participants with type 1 diabetes, consisting of two subgroups (7 young [23 ± 4 years] and 10 older [54 ± 4 years] participants), with 23 controls (13 young, 24 ± 4 years; 10 older, 55 ± 4 years). For each participant, one eye was tested with relaxed accommodation. A 3T clinical magnetic resonance imaging scanner was used to image the eye, employing a multiple spin echo (MSE) sequence to determine Lens dimensions and refractive index profiles along the equatorial and axial directions. Results - The diabetes group had significantly smaller Lens equatorial diameters and larger Lens axial thicknesses than the control group (diameter mean ± 95% confidence interval [CI]: diabetes group 8.65 ± 0.26 mm, control group 9.42 ± 0.18 mm; axial thickness: diabetes group 4.33 ± 0.30 mm, control group 3.80 ± 0.14 mm). These differences were also significant within each age group. The older group had significantly greater axial thickness than the young group (older group 4.35 ± 0.26 mm, young group 3.70 ± 0.25 mm). Center refractive indices of diabetes and control groups were not significantly different. There were some statistically significant differences between the refractive index fitting parameters of young and older groups, but not between diabetes and control groups of the same age. Conclusions - Smaller Lens diameters occurred in the diabetes groups than in the age-matched control groups. Differences in refractive index distribution between persons with and without diabetes are too small to have important effects on instruments measuring axial thickness.
Pavan Kumar Verkicharla - One of the best experts on this subject based on the ideXlab platform.
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Change in human Lens dimensions, Lens refractive index distribution and ciliary body ring diameter with accommodation
Biomedical Optics Express, 2018Co-Authors: Adnan Khan, James M. Pope, Pavan Kumar Verkicharla, Marwan Suheimat, David A. AtchisonAbstract:We investigated changes in ciliary body ring diameter, Lens dimensions and Lens refractive index distributions with accommodation in young adults. A 3T clinical magnetic resonance imaging scanner imaged right eyes of 38 18-29 year old participants using a multiple spin echo sequence to determine accommodation-induced changes along Lens axial and equatorial directions. Accommodation stimuli were approximately 1 D and 5 D. With accommodation, ciliary body ring diameter, and equatorial Lens diameter decreased (–0.43 ± 0.31 mm and –0.30 ± 0.23 mm, respectively), and axial Lens thickness increased ( + 0.34 ± 0.16 mm). Lens Shape changes cause redistribution of the Lens internal structure, leading to change in refractive index distribution profiles. With accommodation, in the axial direction refractive index profiles became flatter in the center and steeper near the periphery of the Lens, while in the equatorial direction they became steeper in the center and flatter in the periphery. The results suggest that the anatomical accuracy of Lens optical models can be improved by accounting for changes in the refractive index profile during accommodation.
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Lens Shape and Refractive Index Distribution in Type 1 Diabetes.
Investigative ophthalmology & visual science, 2015Co-Authors: Adnan, James M. Pope, Pavan Kumar Verkicharla, Marwan Suheimat, Farshid Sepehrband, Sanjeev Kasthurirangan, David A. AtchisonAbstract:Purpose - To compare Lens dimensions and refractive index distributions in type 1 diabetes and age-matched control groups. Methods - There were 17 participants with type 1 diabetes, consisting of two subgroups (7 young [23 ± 4 years] and 10 older [54 ± 4 years] participants), with 23 controls (13 young, 24 ± 4 years; 10 older, 55 ± 4 years). For each participant, one eye was tested with relaxed accommodation. A 3T clinical magnetic resonance imaging scanner was used to image the eye, employing a multiple spin echo (MSE) sequence to determine Lens dimensions and refractive index profiles along the equatorial and axial directions. Results - The diabetes group had significantly smaller Lens equatorial diameters and larger Lens axial thicknesses than the control group (diameter mean ± 95% confidence interval [CI]: diabetes group 8.65 ± 0.26 mm, control group 9.42 ± 0.18 mm; axial thickness: diabetes group 4.33 ± 0.30 mm, control group 3.80 ± 0.14 mm). These differences were also significant within each age group. The older group had significantly greater axial thickness than the young group (older group 4.35 ± 0.26 mm, young group 3.70 ± 0.25 mm). Center refractive indices of diabetes and control groups were not significantly different. There were some statistically significant differences between the refractive index fitting parameters of young and older groups, but not between diabetes and control groups of the same age. Conclusions - Smaller Lens diameters occurred in the diabetes groups than in the age-matched control groups. Differences in refractive index distribution between persons with and without diabetes are too small to have important effects on instruments measuring axial thickness.