The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
John M. Prausnitz - One of the best experts on this subject based on the ideXlab platform.
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Post-Lens tear-film depletion due to evaporative dehydration of a Soft Contact Lens
Journal of Membrane Science, 2005Co-Authors: Francesco Fornasiero, John M. Prausnitz, Clayton J. RadkeAbstract:Abstract For a Soft-Contact-Lens (SCL) wearer, corneal health and comfort are strongly influenced by water transport through the polymeric materials used in Lens fabrication. In particular, evaporative water loss at the anterior Lens surface is a potential cause of Contact-Lens dehydration and of post-Lens tear-film depletion, which in turn, may lead to discomfort, dryness syndrome, and/or Lens adhesion. We present a solution–diffusion model for transport of water through Soft-Contact-Lens materials to mimic evaporative dehydration from a Contact Lens during blinking and to access possible SCL adhesion to the corneal surface under a variety of environmental conditions (e.g., wind speed and relative humidity). To describe the water-transport process, we use an extended version of the Maxwell–Stefan multicomponent diffusion equation for species that differ starkly in size (i.e., water and the polymer matrix). To describe thermodynamic properties of the Soft-Contact-Lens/water mixture, we use a modified Flory–Rehner theory for polymer solutions. The proposed transport model is applied to two typical SCL materials: a low-water-content (38 wt.%) polymacon SCL (SofLens® 38), and a high-water-content (70 wt.%) hilafilcon A SCL (SofLens™ One Day). We calculate that a SCL on the eye loses water within a few minutes from Lens insertion until it reaches a periodic steady state, with an average water content a few percent lower than the initial saturated water content. When the external relative humidity is low and the wind speed is high, the periodic-steady net flux of water from the post-Lens tear film (PoLTF) through the Contact Lens toward the environment is comparable to the supply of water to the PoLTF from the eye anterior chamber. Thus, PoLTF depletion may occur at these conditions, leading to undesired, reduced SCL on-eye movement or, perhaps, to SCL adhesion on the ocular surface. Also, our calculations show that, at the most dehydrating conditions, the high-water-content hilafilcon A Lens is more prone to dehydration and PoLTF depletion than is the low-water-content polymacon Lens with the same thickness. However, at the least dehydrating conditions this trend is reversed. Relative humidity, wind speed, and Lens thickness significantly influence SCL dehydration.
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Glass-transition temperatures for Soft-Contact-Lens materials. Dependence on water content
Polymer, 2005Co-Authors: Francesco Fornasiero, Marie Ung, Clayton J. Radke, John M. PrausnitzAbstract:Abstract Glass-transition temperatures for three Soft-Contact-Lens (SCL) materials are measured by modulated differential scanning calorimetry as a function of SCL hydration, as determined by thermogravimetric analysis. The SCL materials are: a conventional hydrogel (SofLens ® 38, polymacon) with a low water content at saturation; a conventional hydrogel (SofLens™ One Day, hilafilcon A) with a high water content at saturation; and a siloxane–hydrogel (PureVision™, balafilcon A). Polymacon, hilafilcon A, and balafilcon A turn glassy at 35 °C when their water contents drop below 10.4, 13.5, and 6 wt%, respectively. These water contents correspond to the equilibrium water uptake at 35 °C for polymacon, hilafilcon A, and balafilcon A at relative humidities, RH, of 74, 64, and 57%, respectively. Our results suggest that the outer surface of a Soft Contact Lens worn on the eye may develop a glassy skin when exposed to air at low relative humidity. This glassy skin may alter fluid transport through the Soft Contact Lens, and influence SCL-wear comfort.
Clayton J. Radke - One of the best experts on this subject based on the ideXlab platform.
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Post-Lens tear-film depletion due to evaporative dehydration of a Soft Contact Lens
Journal of Membrane Science, 2005Co-Authors: Francesco Fornasiero, John M. Prausnitz, Clayton J. RadkeAbstract:Abstract For a Soft-Contact-Lens (SCL) wearer, corneal health and comfort are strongly influenced by water transport through the polymeric materials used in Lens fabrication. In particular, evaporative water loss at the anterior Lens surface is a potential cause of Contact-Lens dehydration and of post-Lens tear-film depletion, which in turn, may lead to discomfort, dryness syndrome, and/or Lens adhesion. We present a solution–diffusion model for transport of water through Soft-Contact-Lens materials to mimic evaporative dehydration from a Contact Lens during blinking and to access possible SCL adhesion to the corneal surface under a variety of environmental conditions (e.g., wind speed and relative humidity). To describe the water-transport process, we use an extended version of the Maxwell–Stefan multicomponent diffusion equation for species that differ starkly in size (i.e., water and the polymer matrix). To describe thermodynamic properties of the Soft-Contact-Lens/water mixture, we use a modified Flory–Rehner theory for polymer solutions. The proposed transport model is applied to two typical SCL materials: a low-water-content (38 wt.%) polymacon SCL (SofLens® 38), and a high-water-content (70 wt.%) hilafilcon A SCL (SofLens™ One Day). We calculate that a SCL on the eye loses water within a few minutes from Lens insertion until it reaches a periodic steady state, with an average water content a few percent lower than the initial saturated water content. When the external relative humidity is low and the wind speed is high, the periodic-steady net flux of water from the post-Lens tear film (PoLTF) through the Contact Lens toward the environment is comparable to the supply of water to the PoLTF from the eye anterior chamber. Thus, PoLTF depletion may occur at these conditions, leading to undesired, reduced SCL on-eye movement or, perhaps, to SCL adhesion on the ocular surface. Also, our calculations show that, at the most dehydrating conditions, the high-water-content hilafilcon A Lens is more prone to dehydration and PoLTF depletion than is the low-water-content polymacon Lens with the same thickness. However, at the least dehydrating conditions this trend is reversed. Relative humidity, wind speed, and Lens thickness significantly influence SCL dehydration.
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Glass-transition temperatures for Soft-Contact-Lens materials. Dependence on water content
Polymer, 2005Co-Authors: Francesco Fornasiero, Marie Ung, Clayton J. Radke, John M. PrausnitzAbstract:Abstract Glass-transition temperatures for three Soft-Contact-Lens (SCL) materials are measured by modulated differential scanning calorimetry as a function of SCL hydration, as determined by thermogravimetric analysis. The SCL materials are: a conventional hydrogel (SofLens ® 38, polymacon) with a low water content at saturation; a conventional hydrogel (SofLens™ One Day, hilafilcon A) with a high water content at saturation; and a siloxane–hydrogel (PureVision™, balafilcon A). Polymacon, hilafilcon A, and balafilcon A turn glassy at 35 °C when their water contents drop below 10.4, 13.5, and 6 wt%, respectively. These water contents correspond to the equilibrium water uptake at 35 °C for polymacon, hilafilcon A, and balafilcon A at relative humidities, RH, of 74, 64, and 57%, respectively. Our results suggest that the outer surface of a Soft Contact Lens worn on the eye may develop a glassy skin when exposed to air at low relative humidity. This glassy skin may alter fluid transport through the Soft Contact Lens, and influence SCL-wear comfort.
Francesco Fornasiero - One of the best experts on this subject based on the ideXlab platform.
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Post-Lens tear-film depletion due to evaporative dehydration of a Soft Contact Lens
Journal of Membrane Science, 2005Co-Authors: Francesco Fornasiero, John M. Prausnitz, Clayton J. RadkeAbstract:Abstract For a Soft-Contact-Lens (SCL) wearer, corneal health and comfort are strongly influenced by water transport through the polymeric materials used in Lens fabrication. In particular, evaporative water loss at the anterior Lens surface is a potential cause of Contact-Lens dehydration and of post-Lens tear-film depletion, which in turn, may lead to discomfort, dryness syndrome, and/or Lens adhesion. We present a solution–diffusion model for transport of water through Soft-Contact-Lens materials to mimic evaporative dehydration from a Contact Lens during blinking and to access possible SCL adhesion to the corneal surface under a variety of environmental conditions (e.g., wind speed and relative humidity). To describe the water-transport process, we use an extended version of the Maxwell–Stefan multicomponent diffusion equation for species that differ starkly in size (i.e., water and the polymer matrix). To describe thermodynamic properties of the Soft-Contact-Lens/water mixture, we use a modified Flory–Rehner theory for polymer solutions. The proposed transport model is applied to two typical SCL materials: a low-water-content (38 wt.%) polymacon SCL (SofLens® 38), and a high-water-content (70 wt.%) hilafilcon A SCL (SofLens™ One Day). We calculate that a SCL on the eye loses water within a few minutes from Lens insertion until it reaches a periodic steady state, with an average water content a few percent lower than the initial saturated water content. When the external relative humidity is low and the wind speed is high, the periodic-steady net flux of water from the post-Lens tear film (PoLTF) through the Contact Lens toward the environment is comparable to the supply of water to the PoLTF from the eye anterior chamber. Thus, PoLTF depletion may occur at these conditions, leading to undesired, reduced SCL on-eye movement or, perhaps, to SCL adhesion on the ocular surface. Also, our calculations show that, at the most dehydrating conditions, the high-water-content hilafilcon A Lens is more prone to dehydration and PoLTF depletion than is the low-water-content polymacon Lens with the same thickness. However, at the least dehydrating conditions this trend is reversed. Relative humidity, wind speed, and Lens thickness significantly influence SCL dehydration.
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Glass-transition temperatures for Soft-Contact-Lens materials. Dependence on water content
Polymer, 2005Co-Authors: Francesco Fornasiero, Marie Ung, Clayton J. Radke, John M. PrausnitzAbstract:Abstract Glass-transition temperatures for three Soft-Contact-Lens (SCL) materials are measured by modulated differential scanning calorimetry as a function of SCL hydration, as determined by thermogravimetric analysis. The SCL materials are: a conventional hydrogel (SofLens ® 38, polymacon) with a low water content at saturation; a conventional hydrogel (SofLens™ One Day, hilafilcon A) with a high water content at saturation; and a siloxane–hydrogel (PureVision™, balafilcon A). Polymacon, hilafilcon A, and balafilcon A turn glassy at 35 °C when their water contents drop below 10.4, 13.5, and 6 wt%, respectively. These water contents correspond to the equilibrium water uptake at 35 °C for polymacon, hilafilcon A, and balafilcon A at relative humidities, RH, of 74, 64, and 57%, respectively. Our results suggest that the outer surface of a Soft Contact Lens worn on the eye may develop a glassy skin when exposed to air at low relative humidity. This glassy skin may alter fluid transport through the Soft Contact Lens, and influence SCL-wear comfort.
Mehdi Khabazkhoob - One of the best experts on this subject based on the ideXlab platform.
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Corneal Biomechanical Changes Following Toric Soft Contact Lens Wear.
Journal of ophthalmic & vision research, 2016Co-Authors: Somayeh Radaie-moghadam, Hassan Hashemi, Ebrahim Jafarzadehpur, Abbasali Yekta, Mehdi KhabazkhoobAbstract:Purpose: To determine the effect of using toric Soft Contact Lenses on corneal biomechanical properties. Methods: We enrolled 33 healthy patients with mean age of 23.18 ± 4.06 and minimal cylinder power of 1 D (-1.98 ± 0.808 SD) and negative history of Contact Lens use; keratoconic patients were excluded from the study. Toric Soft Contact Lenses (BIOFINITY, Comfilcon A, Coopervision, Southampton, UK) were fitted in all participants. The Ocular Response Analyzer (Reichert Ophthalmic Instruments, Depew, New York, USA) was used to measure corneal hysteresis (CH), corneal resistance factor (CRF), and the Pentacam HR (Oculus, Inc., Lynnwood, WA, USA) was used to measure central corneal thickness (CCT) and mean keratometry (K mean) before and one week, one month, and three months after using the toric Soft Contact Lenses. Results: CH and CRF were decreased significantly one month after using the Contact Lens; mean CH decreased from 9.99 ± 1.44 to 9.59 ± 1.54 mmHg, and mean CRF decreased from 9.96 ± 1.71 to 9.63 ± 1.73 mmHg ( P = 0.013 and P = 0.017, respectively). Mean CCT and K mean did not show a significant change during the period of toric Soft Contact Lens use. Conclusion: CH and CRF decreased significantly one month after fitting toric Soft Contact Lenses while CCT and K mean did not change significantly. Corneal biomechanical parameters may alter with toric Soft Contact Lens use and such changes may have implications with long-term use such Lenses.
Nathan Efron - One of the best experts on this subject based on the ideXlab platform.
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Water properties of Soft Contact Lens materials
Contact Lens and Anterior Eye, 2004Co-Authors: Ioannis Tranoudis, Nathan EfronAbstract:The properties of water in Soft Contact Lenses such as the water content, free-to-bound water ratio, and the extent to which Soft Lenses dehydrate during wear, are key determinants of their in eye performance and oxygen transmissibility characteristics. This study describes clinical and laboratory experiments that were conducted in order to examine the state of water in eight Soft Contact Lenses manufactured from different materials. Specifically, Lenses made from the following eight materials (and nominal water contents) were used: HEMA/VP 40%, HEMA/VP 55%, HEMA/VP 70%, VP/MMA 55%, VP/MMA 70%, HEMA 40%, HEMA/MAA 55% and HEMA/MAA 70% [HEMA = 2-hydroxy-ethyl methacrylate, VP = vinyl pyrrolidone, MMA = methyl methacrylate, MAA = methacrylic acid]. Differential scanning calorimetry (DSC) was used for measuring the free water content in the materials listed above. Some noticeable differences in water properties among Soft Contact Lens materials having approximately the same water contents were revealed. Low water content materials exhibited a simple endotherm and all water melted around 0 °C. On the other hand, medium and high water content materials exhibited multiple melting endotherms, representing a broad range of interactions between water and the polymer. Low water content Soft Contact Lenses have approximately the same amount of bound water as those with much higher water contents. Six subjects were then fitted with the same Lenses for one day. In vitro measurements of water content and oxygen transmissibility were taken at 35 °C, both before Lens fitting and after 6 h of Lens wear. Water content and oxygen transmissibility were correlated with the water properties of the Soft Contact Lens materials. The relative change in Lens water content (%ΔWC) and relative change in Lens oxygen transmissibility (%ΔDk/t) were calculated and correlated with the water properties of the eight Soft Contact Lens materials. It was concluded that (a) oxygen transmissibility, free water content and free-to-bound water ratio are increased when the water content of a Contact Lens is increased and (b) water content, free water content and free-to-bound water ratio cannot be used for the prediction of Soft Contact Lens dehydration in vivo. © 2004 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.
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morphology of corneal nerves in Soft Contact Lens wear a comparative study using confocal microscopy
Ophthalmic and Physiological Optics, 2003Co-Authors: Laura Oliveirasoto, Nathan EfronAbstract:The aim of this study was to evaluate corneal innervation in Soft Contact Lens wearers using the Tomey Confoscan confocal microscope (40×/0.75 objective Lens). Three distinct age- and sex-matched subject groups were involved, including extended Soft (hydrogel and silicone-hydrogel) Contact Lens wearers, overnight Soft (hydrogel) Contact Lens wearers, and non Contact Lens wearers. A number of variables were objectively measured, subjectively evaluated, or graded in order to investigate the distribution and morphology of corneal nerves. For most of the evaluated parameters, no statistically significant differences were found. However, qualitative observations showed noticeable differences in corneal nerve appearance among the different subject groups; the degree of corneal oedema was suggested as the main causative factor. In conclusion, neither the short-term (overnight wear) nor the long-term (12-month extended wear) Soft Contact Lens wear appeared to affect the morphology and/or distribution of corneal nerves as viewed with confocal microscopy.
