Comparison of the Coulometric and Polarographic Measurement of a High-Dk Hydrogel

Morgan, Courtney F.; Brennan, Noel A.; Alvord, Larry

doi:10.1097/00006324-200101010-00010

Cited by 22 publications

(12 citation statements)

References 3 publications

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“…Oxygen permeability (Dk) and oxygen transmissibility (Dk/t) of contact lenses can be measured using either coulometric or polarographic techniques [11]. Coulometric methods use a nitrogen carrier gas to transport oxygen that has permeated through a lens to an oxygen detector.…”

Section: Oxygen Permeabilitymentioning

confidence: 99%

BCLA CLEAR - Contact lens wettability, cleaning, disinfection and interactions with tears

Willcox

Keir

Maseedupally

et al. 2021

Contact Lens and Anterior Eye

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Contact lens materials have undergone significant changes over the past 20 years, particularly with respect to the introduction of silicone hydrogel materials. Whilst this development addressed hypoxic issues, other important areas relating to contact lens success, notably comfort, require further research.Contact lens wettability remains a crucially important part of biocompatibility. Contact lenses can be made more wettable by incorporation of surfactants into blister packs, internal wetting agents, surface treatments or care solutions. However, there remains no clear association between contact lens wettability and comfort, making it challenging to determine the potential for these approaches to be of significant clinical benefit. Most contact lenses are used on a daily wear, reusable basis, which requires them to be disinfected when not worn. The ideal disinfecting solution would also improve comfort during wear. However, balancing these requirements with other factors, including biocompatibility, remains a challenge. Soft lens materials invariably take up and subsequently release certain components of disinfecting solutions onto the ocular surface. This may affect tear film stability and the normal ocular microbiome, and further research is needed in this area to determine whether this has any affect on comfort. Finally, contact lens materials sorb components of the tear film, and these interactions are complex and may change the biochemistry of the tear film, which in turn may affect their comfort.In conclusion, the interaction between lens materials, tear film and disinfection solution plays an important role in the biocompatibility of lenses. However, the exact role and whether this can be altered to improve biocompatibility and comfort during wear remains debatable. This report summarises the best available evidence to examine this complex relationship and the opportunities for practitioners to enhance in-eye comfort of contemporary lenses, along with providing suggestions for areas of study that may provide further information on this topic.

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Section: Oxygen Permeabilitymentioning

confidence: 99%

BCLA CLEAR - Contact lens wettability, cleaning, disinfection and interactions with tears

Willcox

Keir

Maseedupally

et al. 2021

Contact Lens and Anterior Eye

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“…34 Despite this, both methods are currently used to obtain Dk/t and Dk coefficients of modern high-Dk (>100 barrer) Si-Hy CLs, with satisfactory results, according to the nominal values given by the manufacturers. 10,30,35 Morgan et al 34 evaluated the oxygen transmissibility and permeability of lotrafilcon A (Focus Night & Day, CIBA Vision; Duluth, GA), obtaining some discrepancies between the coulometric (in the liquid-gas configuration) and polarographic techniques for lotrafilcon A and other RGP materials with permeability coefficients higher than 70 barrer. The discrepancies not only affect the mean values but also the standard error, which is larger with the polarographic technique.…”

Section: Introductionmentioning

confidence: 99%

Determination of Oxygen Permeability in Soft Contact Lenses Using a Polarographic Method: Estimation of Relevant Physiological Parameters

González-Meijóme

Compañ-Moreno

Riande

2008

Ind. Eng. Chem. Res.

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This work reports the apparent oxygen transmissibility Dk/t) app of four silicone hydrogel (Si-Hy) contact lenses (CLs). A method is described that allows the estimation of the oxygen tension at the lens-cornea interface for closed-and open-eyelids situations combining the instrument oxygen transmissibility (IOT) and corneal parameters such as corneal thickness, corneal permeability, and oxygen flux across the cornea. From these results, the biological oxygen apparent transmissibility (BOAT), equivalent oxygen percentage (EOP), partial pressure, (p tc ), of oxygen at the cornea-CL interface and oxygen flux, (j c ), were also obtained. This method allows the evaluation of the physiological environment under the lens using the formulations described in previous studies. The oxygen performance of four Si-Hy materials was evaluated using a polarographic cell coupled to a permeometer. Measurements of the apparent transmissibility, (Dk/t) app , and permeability, Dk, were performed in stacks containing from 1 to n repeated lenses and, from the values obtained, the error involved in the measurements in single samples was estimated. It was found that the values of (Dk/t) app and Dk obtained following the two different procedures (stack method and measurement of single sample) were significantly different from the nominal values given by the manufacturer, particularly for some samples. However, the impact of these differences on the values of the other physiologically relevant parameters (BOAT, EOP, p tc , and j c ) was not significant. Furthermore, these parameters were similar for the four lenses in spite of the different (Dk/t) app measured. The relationships of (Dk/t) app with the remaining physiological parameters were calculated and graphically represented for open and closed-eyelid conditions.

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“…[20][21][22][23][24] However, to our best knowledge, D and k values are not available for current high-Dk SCLs. Measurement of D and k for high-Dk lenses is difficult compared to that for low-Dk lenses because of faster response time (small lens thickness and large diffusivity), edge effects, 17,25 significant boundary-layer resistances, 18,19,22,24,26 and lens desiccation. 26,27 On the basis of our earlier work on high-Dk measurements, 28 we here overcome the difficulties encountered in measuring oxygen diffusivity and solubility for hypertransmissible SCLs.…”

Section: Introductionmentioning

confidence: 99%

“…Some previous measurements of oxygen diffusivity and solubility have been carried out for low- Dk hydrogel lenses , or for various membranes. − However, to our best knowledge, D and k values are not available for current high- Dk SCLs. Measurement of D and k for high- Dk lenses is difficult compared to that for low- Dk lenses because of faster response time (small lens thickness and large diffusivity), edge effects, , significant boundary-layer resistances, ,,,, and lens desiccation. , On the basis of our earlier work on high- Dk measurements, we here overcome the difficulties encountered in measuring oxygen diffusivity and solubility for hypertransmissible SCLs. An improved electrochemistry-based polarographic method reports the transient current response of the lens to a step change in oxygen concentration, thereby enabling measurement of D and k .…”

Section: Introductionmentioning

confidence: 99%

Polarographic Method for Measuring Oxygen Diffusivity and Solubility in Water-Saturated Polymer Films: Application to Hypertransmissible Soft Contact Lenses

Chhabra

Prausnitz

Radke

2008

Ind. Eng. Chem. Res.

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An electrochemical-polarographic method is described for measuring the diffusivity, D, and solubility, k, of oxygen in aqueous-saturated polymer films. While the apparatus and procedure are general for such films, it is here applied to determine D and k for oxygen in hypertransmissible soft contact lenses. Usually, only oxygen permeability, P, the product of D and k, is measured because P gauges the steady flux of oxygen through hydrogel membranes. However, we utilize the polarographic technique in the unsteady state and, hence, obtain D and k separately. Determination of each of these properties is critical for designing better lens materials that ensure sufficient oxygen supply to the cornea. We have measured oxygen diffusivities and solubilities for nine commercial soft contact lenses. Our data indicate that oxygen diffusivity is primarily responsible for the range of oxygen permeability observed for hypertransmissible soft contact lenses. For 2-hydroxyethyl methacrylate (HEMA)-based lenses, measured solubilities suggest that over 90% of the dissolved oxygen partitions to the polymer phase.

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Comparison of the Coulometric and Polarographic Measurement of a High-Dk Hydrogel

Abstract: The coulometric method is preferable for the measurement of contact lens materials with permeability >70 barrer. The coulometric method was successfully modified to include hydrogels.

Cited by 22 publications

References 3 publications

BCLA CLEAR - Contact lens wettability, cleaning, disinfection and interactions with tears

BCLA CLEAR - Contact lens wettability, cleaning, disinfection and interactions with tears

Determination of Oxygen Permeability in Soft Contact Lenses Using a Polarographic Method: Estimation of Relevant Physiological Parameters

Polarographic Method for Measuring Oxygen Diffusivity and Solubility in Water-Saturated Polymer Films: Application to Hypertransmissible Soft Contact Lenses

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