Comments to paper entitled "Predicting scleral GP lens entrapped tear layer oxygen tensions"

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Oxygen and ionic transport in hydrogel and silicone-hydrogel contact lens materials : an experimental and theoretical study

The transport of oxygen, water and naked ions of Na+ and Cl− across two kind of hydrogels materials, made of a conventional hydrogel (Hy) based on hydroxyethyl methacrylate (pHEMA) and a silicone hydrogel (Si-Hy) material containing siloxane moieties, was compared between Molecular Dynamics Simulations (MDS) and experimental measurements. Computer-assisted simulations were carried out for wet hydrogels at 310 K and equilibrium water uptake in the range from 10% to 40%. Our results show that in Si-Hy materials the aqueous hydrogel and hydrophobic siloxane phases are separated suggesting a co-continuous structure, and oxygen moves predominantly through the free volume of the hydrophobic siloxane phase. The values of diffusion coefficient of O2, water and Na+ and Cl− ions in Si-Hy was about one order of magnitude higher than in conventional hydrogels when the water content was above 25 wt% up to a critical value of 35 wt% where a percolation phenomenon is observed. The value of the oxygen diffusion coefficient obtained by simulations are roughly similar to that experimentally found using potentiostatic techniques. Values found experimentally for Na+ diffusion coefficients are between three or five times lower than MDS. For Si-Hy materials with 36 wt% of water the Na+ permeability, diffusion coefficient and salt partition coefficient (km=P/D) are 6.7±0.2×10−7 cm2/s, 1.8±0.5×10−6 cm2/s and 0.42±0.13, respectively. For Hy materials of 38.6 wt% the values found were 18.4±1.2×10−7 cm2/s, 5.4±1.0×10−6 cm2/s and 0.34±0.09, respectively. The coordination number between the fixed groups (3SiO3) and water in HEMA and the particles (O2, Cl− and Na+) is slightly larger than unity. The present study might be applied in the modeling of the gas transport in hydrogels as well as in novel polymeric structures for novel polymeric structures for new biomedical and technological applications with the aim of predicting and tuning their physiological behavior.This work was supported by the project MAT2010-17091 from the Spanish Ministry of Science and Innovation

CLEAR - Orthokeratology

NoOrthokeratology (ortho-k) is the process of deliberately reshaping the anterior cornea by utilising specialty contact lenses to temporarily and reversibly reduce refractive error after lens removal. Modern ortho-k utilises reverse geometry lens designs, made with highly oxygen permeable rigid materials, worn overnight to reshape the anterior cornea and provide temporary correction of refractive error. More recently, ortho-k has been extensively used to slow the progression of myopia in children. This report reviews the practice of ortho-k, including its history, mechanisms of refractive and ocular changes, current use in the correction of myopia, astigmatism, hyperopia, and presbyopia, and standard of care. Suitable candidates for ortho-k are described, along with the fitting process, factors impacting success, and the potential options for using newer lens designs. Ocular changes associated with ortho-k, such as alterations in corneal thickness, development of microcysts, pigmented arcs, and fibrillary lines are reviewed. The safety of ortho-k is extensively reviewed, along with an overview of non-compliant behaviours and appropriate disinfection regimens. Finally, the role of ortho-k in myopia management for children is discussed in terms of efficacy, safety, and potential mechanisms of myopia control, including the impact of factors such as initial fitting age, baseline refractive error, the role of peripheral defocus, higher order aberrations, pupil size, and treatment zone size.The CLEAR initiative was facilitated by the BCLA, with financial support by way of Educational Grants for collaboration, publication and dissemination provided by Alcon and CooperVision

Light disturbance analysis in the controlled randomized clinical trial MiSight assessment study Spain (MASS)

Purpose: To evaluate the perception of light disturbances (LD) in children wearing Dual Focus (DF) MiSight (R) contact lenses (CLs) for myopia control compared with children wearing single vision spectacles (SV).Methods: This was a randomized, controlled clinical trial involving subjects aged 8-12 with myopia of -0.75 to -4.00D and astigmatism 0.05). However, monocular BFCIrreg. as well as monocular and binocular BFCIrreg.SD showed a significant decrease at 24 month visit compared with 12 month visit.Conclusions: DF lenses increase the monocular light disturbance perception compared with a single vision spectacle correction. However, this effect decreased over the follow-up time and presented a significant binocular attenuation effect.This study has been funded in part by projects PTDC/SAU-BEB/098392/2008 and PTDC/SAU-BEB/098391/2008, which in turn have been funded by the Portuguese Fundação para a Ciência e Tecnologia through the European Social Fund and by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project UID/FIS/04650/2013. JMG-M has proprietary interests in the experimental device used to measure light disturbance.CooperVision S.L. Spain also provided financial support. CooperVision S.L. provided the study contact lenses and the funding to carry out the clinical trial. The sponsor had no role in designing or conducting this research