Contact Lens Materials Research Articles

Comparison of Tear Film Surface Quality Measured In Vivo on Water Gradient Silicone Hydrogel and Hydrogel Contact Lenses

Recently, a new water gradient silicone hydrogel material has been introduced for a daily disposable lens. The aim of this study was to assess, in vivo, the prelens tear film surface quality (TFSQ) of this new lens in comparison with that of another daily disposable lens from the same manufacturer. Eleven subjects wore two pairs of hydrogel nelfilcon A and silicone hydrogel delefilcon A lenses in two nonconsecutive days. The noninvasive lateral shearing interferometry was used to analyze the prelens tear film and distinguish between different contact lens materials. Measurements were taken in natural blinking conditions after 6 hours of wear. Additionally, the subjective comfort was evaluated. The presence of both lenses resulted in a TFSQ reduction as compared with the bare eye condition. Statistically significant (Wilcoxon rank sum test, P<0.012) smaller change in TFSQ was introduced by the water gradient material than the high water content material. A statistically significant correlation between the TFSQ results of the two lenses was found (Pearson correlation coefficient R=0.8, P<0.003), indicating high linearity of the measurement methodology with respect to the tested lens material. The correlation of subjective comfort in lenses was lower and found to be insignificant (R=0.6, P>0.05). Although the prelens TFSQ is not always directly proportional to the lens water content, the results of the in vivo study showed that the new water gradient silicone hydrogel material impact less TFSQ as compared with its predecessor.

Characterization of materials for commercial and new nanophotonic soft contact lenses by optomagnetic spectroscopy

The contact lens industry and market have displayed a high level of dynamism in the past few decades, and have evolved into a rapidly changing field in which science and everyday practice constantly interact. This work presents the comparative research of characteristics of the basic (commercial) material and nanophotonic materials which were obtained by incorporation of fullerene nanoparticles and its derivate in basic material for soft contact lenses. Basic contact lens material was sintetized of monomer 2-hydroxyethyl methacrylate (HEMA), and fullerene and its derivates were used due to their good transmission characteristics in ultraviolet, visible and near infra-red spectrum. For the purposes of characterization of materials for soft contact lenses Optomagnetic Spectroscopy (OMS) was used. OMS is based on difference between diffusely reflected white light and reflected polarized white light. This research contributes to applied optical science and biomedical application industry.

Influence of specimen thickness on the nanoindentation of hydrogels: Measuring the mechanical properties of soft contact lenses

Nanoindentation offers a convenient method for the testing of thin hydrogel specimens, such as contact lenses, to directly assess their mechanical properties. Here we investigate the mechanical properties of poly(hydroxyethyl methacrylate) (pHEMA) specimens of a range of uniform thickness values and demonstrate that, with 50 and 100μm radius spherical indenters, a significant increase in apparent elastic modulus is seen when the specimen thickness is smaller than 500μm at indentation depths <1μm. This is a manifestation of the well known indentation thickness effect but occurring at larger critical thicknesses than seen with other materials. A simple empirical relation is determined for the variation in apparent elastic modulus with normalised thickness. The empirical thickness correction function obtained from pHEMA specimens was subsequently used to correct for the thickness variation within a range of contact lenses supplied by a number of different manufacturers fabricated from both pHEMA and silicone polymers, with a range of optical strengths and hence thickness profiles. The correction function is seen to compensate for the variation in apparent elastic modulus with lens thickness for all four contact lens types, irrespective of lens material. The measured Young's modulus of the contact lens material, corrected for thickness, was compared with that quoted by the manufacturers of the contact lenses, obtained by conventional bulk mechanical testing, to find good agreement.

In vitro efficiency of contact lens care solutions in removing cholesterol deposits from silicone hydrogel contact lenses

Purpose: To determine the efficiency of multi- purpose solutions (MPS) and saline in removing cholesterol deposits from silicone hydrogel (SH) contact lens materials using an in vitro model.

Dynamic contact angle analysis of silicone hydrogel contact lenses using the Wilhelmy plate technique

Purpose: The literature on the use of the Wilhelmy plate technique for the analysis of contact lenses is somewhat limited; there is perhaps only one paper which compared a range of contact lens materials using the technique. This is possibly due to complications associated with its use in the analysis of such materials. The aim of this work is to analyse a range of silicone-based hydrogel contact lens materials using the technique.

Characterising dehydration resistance in soft contact lens materials

Purpose: The term “dehydration resistance” is frequently used in connection with contact lens materials but there is no agreed assessment technique. On one hand the absolute mass or the relative proportion of water lost has been proposed, and on the other the change that water loss induces in the resultant lens surface. An additional approach, suggested for silicone hydrogel lenses, is measurement of “water binding” characteristics of the fully hydrated lens. This poster compares the meaning and potential clinical relevance of various approaches.

50 years of contact lenses: How has the modulus changed?

Purpose: As contact lens materials have developed, the relevance of mechanical properties and particularly the modulus (stiffness) has been a matter of considerable debate. As poly(methyl methacrylate) (PMMA) began to be replaced by more oxygen permeable materials, dimensional stability and lens durability were key concerns. The spectrum of materials used for manufacture has since expanded to encompass much softer hydrogels. Although modulus was initially used as a comparative factor for specific aspects of materials performance, is now understood to influence factors such as initial comfort. The aim of this poster is to explore modulus changes over the last 50 years.

Astigmatism and soft torics–the challenge or is it?”

Astigmatism and soft torics–the challenge or is it?”

Relationship between contact lens coefficient of friction and subjective lens comfort

Purpose: Examine the relationship between comfort and contact lens coefficient of friction (CoF) among soft contact lens materials.

A report card on hydrogel contact lens materials: Where are we and what's new and novel?

A report card on hydrogel contact lens materials: Where are we and what's new and novel?

KEYNOTE ADDRESS: Surface properties and ocular compatibility of silicone hydrogels

The last decade has been very significant for the development of contact lens materials. The most important feature of this period has been the appearance, increasing diversity and market growth of the so-called silicone hydrogels. Both name and oxygen transport properties are a direct consequence of the inclusion of a significant proportion of siloxy groups, which contain the element silicon linked directly to both oxygen and carbon atoms. Because of their enhanced oxygen permeability, the initial focus of silicone hydrogels was extended wear.

Release of ciprofloxacin and dexamethasone from commercial contact lens materials

Release of ciprofloxacin and dexamethasone from commercial contact lens materials

Contact lenses–what to expect in your pre- reg year

Contact lenses–what to expect in your pre- reg year

A laboratory assessment of factors that affect bacterial adhesion to contact lenses.

Adhesion of pathogenic microbes, particularly bacteria, to contact lenses is implicated in contact lens related microbial adverse events. Various in vitro conditions such as type of bacteria, the size of initial inoculum, contact lens material, nutritional content of media, and incubation period can influence bacterial adhesion to contact lenses and the current study investigated the effect of these conditions on bacterial adhesion to contact lenses. There was no significant difference in numbers of bacteria that adhered to hydrogel etafilcon A or silicone hydrogel senofilcon A contact lenses. Pseudomonas aeruginosa adhered in higher numbers compared to Staphylococcus aureus. Within a genera/species, adhesion of different bacterial strains did not differ appreciably. The size of initial inoculum, nutritional content of media, and incubation period played significant roles in bacterial adhesion to lenses. A set of in vitro assay conditions to help standardize adhesion between studies have been recommended.

The TFOS International Workshop on Contact Lens Discomfort: Report of the Contact Lens Materials, Design, and Care Subcommittee

Jones, L., Brennan, N. A., Gonzalez-Meijome, J., Lally, J., Maldonado-Codina, C., Schmidt, T. A., … Nichols, J. J. (2013). The TFOS International Workshop on Contact Lens Discomfort: Report of the Contact Lens Materials, Design, and Care Subcommittee. Investigative Opthalmology & Visual Science, 54(11), TFOS37. https://doi.org/10.1167/iovs.13-13215

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 310K 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 25wt% up to a critical value of 35wt% 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 36wt% of water the Na+ permeability, diffusion coefficient and salt partition coefficient (km=P/D) are 6.7±0.2×10−7cm2/s, 1.8±0.5×10−6cm2/s and 0.42±0.13, respectively. For Hy materials of 38.6wt% the values found were 18.4±1.2×10−7cm2/s, 5.4±1.0×10−6cm2/s and 0.34±0.09, respectively. The coordination number between the fixed groups (SiO) 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.

Preparation, characterization and antimicrobial study of a hydrogel (soft contact lens) material impregnated with silver nanoparticles

Contact lenses that incorporate antimicrobial properties may reduce the risk for microbial-associated adverse events for lens wearers. The aim of this study was to assess the antimicrobial effects of silver nanoparticles (NP) when impregnated in a hydrogel material. Hydrogel disks, used as a proxy for soft contact lenses, were prepared with silver NPs to add an antimicrobial effect to the polymer. Six groups of disks were created, each with a different concentration of silver NPs. The antimicrobial effect of the hydrogels against Pseudomonas aeruginosa (ATCC15442) and Staphylococcus aureus (ATCC6538) was evaluated at 6, 24, 48 and 72 h. Silver NP concentrations ranged from 20.71 to 98.06 μg/disk. All groups demonstrated excellent antibacterial effects against P. aeruginosa at each time point. After 6h all disks didn't exhibit desirable antibacterial activity against S. aureus; whereas except those with 20.71 μg silver NPs showed antibacterial activity at 24h and only the disks with 57.13 and 98.06 μg silver NPs showed antimicrobial activity at 48 and 72 h. The development of contact lenses made of a silver NP-impregnated hydrogel material may bring antimicrobial effects sufficient to decrease the risk of microbial-related adverse events for lens wearers.

Factors that Influence In Vitro Cholesterol Deposition on Contact Lenses

The purpose of this study was to analyze the impact that incubation time, lipid concentration, and solution replenishment have on silicone hydrogel (SiHy) and conventional hydrogel (CH) contact lens cholesterol deposition via in vitro radiochemical experiments. Four SiHy (senofilcon A, lotrafilcon B, comfilcon A, balafilcon A) and two CH (etafilcon A and omafilcon A) contact lenses were incubated in an artificial tear solution (ATS) that contained major tear film proteins, lipids, salts, salts, and a trace amount of radioactive C-cholesterol. Lenses were incubated for various incubation times (1, 3, 7, 14, or 28 days), with three concentrations of lipid (0.5×, 1×, 2× tear film concentration) and with or without solution replenishment to assess each variable's impact on cholesterol deposition. After incubation, the lenses were extracted using 2:1 chloroform:methanol, extracts were analyzed in a beta counter and masses (micrograms per lens) were extrapolated from standard curves. Within the SiHy materials, balafilcon A deposited the greatest amount of cholesterol (p < 0.001) and lotrafilcon B the lowest (p < 0.001). The CH lens materials showed significantly lower uptake amounts than any of the SiHy lens materials (p < 0.001). The uptake of cholesterol ranged from 0.01 ± 0.01 μg/lens to 3.22 ± 0.34 μg/lens for all lens materials. Kinetic uptake of cholesterol was shown to be continuous throughout the 28 days of incubation without plateau (p < 0.001), and varying the lipid concentration did impact the resulting cholesterol deposition (p < 0.001). Replenishing the ATS every other day also affected cholesterol deposition throughout the experiment. Overall, the deposition pattern was 2× > replenishing > 1× > 0.5×. Overall, SiHy lenses deposit significantly more cholesterol than CH lens materials, and the mass of lipid deposited is dependent on the contact lens material, length of incubation, concentration of lipids in the ATS, and the replenishment of ATS.

In vitro uptake and release of natamycin Dex-b-PLA nanoparticles from model contact lens materials

Purpose: To evaluate the uptake and release of the antifungal agent natamycin encapsulated within poly(D,L-lactide)-dextran nanoparticles (Dex-b-PLA NPs) from model contact lens (CL) materials. Methods: Six model CL materials (gel 1:poly(hydroxyethyl methacrylate, pHEMA); gel 2:85% pHEMA: 15% [Tris(trimethylsiloxy)silyl]-propyl methacrylate (TRIS); gel 3: 75% pHEMA: 25% TRIS; gel 4: 85% N,N dimethylacrylamide (DMAA): 15% TRIS; gel 5:75% DMAA: 25% TRIS; and gel 6: DMAA) were prepared using a photoinitiation procedure. The gels were incubated in: (1) natamycin dissolved in deionized (DI) water and (2) natamycin encapsulated within Dex-b-PLA NPs in dimethylsulfoxide/DI water. Natamycin release from these materials was monitored using UV–visible spectrophotometry at 304 nm over 7 d. Results: Natamycin uptake by all model CL materials increased between 1 and 7 d (p < 0.001). The uptake of natamycin-NPs was higher than the uptake of the drug alone in DI water (p < 0.05). Drug release was higher in materials containing DMAA than pHEMA (p < 0.05). All gels loaded with natamycin-NPs also released more drug compared to gels soaked with natamycin in DI water (p < 0.001). After 1 h, CL materials loaded with natamycin alone released 28–82% of the total drug release. With the exception of gel 6, this burst released was reduced to 21–54% for CL materials loaded with natamycin-NPs. Conclusions: Model CL materials loaded with natamycin-Dex-b-PLA NPs were able to release natamycin for up to 12 h under infinite sink conditions. DMAA-TRIS materials may be more suitable for drug delivery of natamycin due to the higher drug release observed with these materials.

Equilibrium Binding Interactions Between Lotrafilcon A Soft Contact Lenses and the Two Prostaglandin Antiglaucoma Drugs Bimatoprost and Tafluprost

To determine the equilibrium binding constant (EB) values of bimatoprost and tafluprost drug product formulations in contact with lotrafilcon A soft contact lenses and to characterize the importance of drug molecule hydrophobicity in controlling the binding interactions. Bimatoprost Ophthalmic Solution and Tafluprost Ophthalmic Solution (Saflutan) were incubated with lotrafilcon A lens material for timed intervals at 25°C and 37°C. Aliquots were withdrawn, filtered, and tested using reverse-phase ultrahigh-performance liquid chromatography with respect to [bimatoprost] or [tafluprost] remaining in the solution. A series of homologous dialkyl phthalate esters and a series of homologous p-hydroxybenzoic acid alkyl esters were also tested as reference compounds. Bimatoprost and tafluprost were rapidly (within 15 min) absorbed from the solution by lotrafilcon A lenses, reaching an equilibrium within 60 min. At any lens:solution (w/v) ratio, the extent of drug binding to lens material was greater for tafluprost than for bimatoprost. The log(EB) values correlated with solute octanol:water partition coefficient (logP) values, indicating that hydrophobic interactions are important in controlling solute partitioning into the lens material. This study established the quantitative relationships between tafluprost and bimatoprost binding to lotrafilcon A lenses. The fraction of bimatoprost or tafluprost that binds to lotrafilcon A increases with increasing lens:solution (w/v) ratio. For a 60 µL dose volume applied to a single contact lens, 16% of initially present bimatoprost remains in the solution, whereas only 6% of initially present tafluprost remains in the solution. These calculations clearly demonstrate that both drugs partition extensively into lotrafilcon A contact lens material. Although the clinical implications of such binding can only be surmised, it would seem prudent to caution contact lens wearers to remove the lenses before administering either prostaglandin drug.